Cover crops for vegetable growers Pam Dawling

Cover Crops for Vegetable
Growers
Cover crops feed and improve the soil, smother
weeds, and prevent soil erosion.
Select cover crops to use opportunities year round.
Fit cover crops into the schedule of vegetable
production.
©Pam Dawling 2016
author of Sustainable Market Farming
www.sustainablemarketfarming.com
www.facebook.com/SustainableMarketFarming

What’s in this presentation
A. Five steps of cover crop planning
B. Reliable cover crops at Twin Oaks
C. Winter cover crops we use at TO
D. Spring and summer cover crops we use
E. Cover crops for pest control
F. Cover crop mixes
G. Small scale equipment and methods
H. Resources

So many possible cover crops
to choose from!
No single solution suits all situations and all times
of year – make careful and informed choices
Experiment with different ideas, take notes
Be flexible about your plans, to take account of
the weather, the crops, the weeds and your
schedule.
Have back-up plans in case the
weather prevents you from
following your original plan

5 steps of cover crop planning
1. Identify your opportunities for cover crops
2. Clarify your cover crop goals for each opportunity
3. Shortlist suitable cover crops for each situation
4. Make a decision from among the options
5. Record your decisions and results, and review for
possible changes next year.
Crimson
clover and
bumble
bee.
Bridget
Aleshire

Step 1 - Cover Crop Opportunities
 In fall after food crops, for winter
– the easiest place to start
 Frost-seeding of small seeds such
as clover, when ground is frozen.
 To replace a crop failure.
 Year-round cover crops/green
fallow
 In late winter or early spring, if
the area will not be planted with
a food crop for 6 weeks or more.
 In spring, summer or fall, 4
weeks or more between one
vegetable crop and a later one
 Undersowing at last cultivation
(oats and soybeans in sweetcorn
shown here, photo by Kathryn Simmons.)

Step 1-
Identify a specific opportunity
• When does the window open?
• When does it close?
• What are the ambient temperatures during that
time? Will there be frosts?
• Will irrigation or rainfall be restricted?
• What is the preceding food crop (avoid the same
family)?
• What is the following food crop (avoid the same
family)?
Broccoli Mustards Kale

Step 2 - Clarify your main goals
Which cover crop benefits are your priorities at that site?
Smother weeds, prevent them growing and seeding
Add organic matter and nutrients
Increase the biological activity in the soil
Reduce erosion by using actively growing roots to anchor
the soil
Improve the tilth of the soil and the sub-soil structure
Improve soil drainage
Improve the soil’s ability to absorb, hold water

Step 2 - Clarify your secondary goals
Salvage leftover nutrients
Fix nitrogen to feed the next crop
Attract beneficial insects
Bio-fumigation for pest or weed control
Kill nematodes

Step 3
Shortlist suitable cover crops
Consult charts and other local growers.
Cover crops divide into 6 groups:
• Cool-season grasses
• Cool-season legumes
• Cool-season broadleaved crops
• Warm-season grasses
• Warm-season legumes
• Warm-season broadleaved crops

Step 3 – Consult Cover Crop Charts
The 9 pages of charts in
Sustainable Market Farming
will help you find cover crops
suitable for your climate, time
of year and time-window.
The SARE book Managing
Cover Crops Profitably is
the best book on the
subject.

Step 4 Fit your cover crop with the
season (fall)
Work back from your farm’s first frost date, to see what options you have.
• 80-120 days before frost - buckwheat, soy, cowpeas, Japanese millet,
sorghum-sudangrass, or a fast vegetable crop.
• 60-80 days before frost - buckwheat, soy, cowpeas, Miami peas,
Japanese millet, sorghum-sudangrass to winter-kill; or oats with
Austrian winter peas, crimson clover, or red clover to grow into winter.
• 40-60 days before frost - oats with soy beans or Miami peas to winter-
kill; or winter barley or winter wheat with Austrian winter peas, crimson
clover, hairy vetch, red clover, fava beans to survive the winter.
• 20-40 days before frost, winter rye, winter wheat, or winter barley, with
crimson clover, Austrian winter peas, red clover or (40 days before frost)
hairy vetch. Too late to usefully sow crops that are not frost-hardy.
• 10 days past the frost date - winter rye or wheat + Austrian winter peas.
• Up to a month past your average frost date - still OK to sow winter rye.

Fit your cover crop with the season
(summer)
• If you have only 28 days until the patch is needed for a
food crop, you can grow mustards or buckwheat. Or
weeds, if you’re careful not to let them seed!
• If you have at least 45 days, you can grow soy or
Japanese millet.
• If you have 50–60 days, Browntop millet is possible.
• In the right climate, sunn hemp can mature
in 60 days.
• With 60–70 days, Sorghum-sudangrass,
German foxtail millet, pearl millet and some
cowpeas will mature.

Step 4: Choose cover crops
matching your main goals
 Smother weeds: sorghum-sudangrass, pearl millet, winter rye,
wheat, barley,oats, buckwheat, brassicas, lupins, red clover,
subterranean clover, berseem clover, soybeans, cowpeas
 Add organic matter, improve the soil’s ability to absorb, hold
water: bulky grasses and legumes , sorghum-sudangrass, millets,
winter rye, velvetbean, cowpeas, sweetclover, sunn hemp
 Increase the biological activity in the soil – use varied mixes
 Reduce erosion: (good roots) grasses especially rye, barley, oats
sweetclover, cowpeas, sub clover,
 Improve the tilth of the soil, the sub-soil structure, soil drainage:
sorghum-sudangrass, sunflower, daikon, sweetclover, crimson
clover, alfalfa, lupins, cowpeas, forage radish, sugar-beet or
forage-beet

Choose cover crops matching your
secondary goals
Scavenge leftover nutrients: (non-leguminous cover
crops) grasses, brassicas (pest and rotation problems),
annual ryegrass (danger of it becoming a weed)
Fix nitrogen: (legumes) clovers, vetches, peas,
cowpeas, soybeans, lentils, sunn-hemp.
Attract beneficial insects: (flowers) buckwheat, peas,
beans, clovers, brassicas, phacelia
Pest or weed control: rye, brassicas, sorghum-sudan,
sunn-hemp, white lupins, sesame.
Kill nematodes: Pacific Gold mustard, white lupins, Iron
and Clay cowpeas, OP French marigolds, sesame

Step 5 - Record decisions & results;
Review for possible changes next year
• Keep notes on how well your cover crops work
for you, and if something goes wrong, what
might work better.
• Winter can offer time to reconfigure planting
schedules to make more future windows for
short-term summer cover crops, or to include
legumes with winter cover crops.

Reliable cover crops at Twin Oaks,
Central Virginia, Zone 7a
Winter cover crops
Grasses:
• Spring Oats
• Winter Wheat
• Winter Rye
Legumes:
• Hairy Vetch
• Crimson Clover
• Austrian Winter Peas
Summer cover crops
Grasses:
• Sorghum-sudangrass
• Japanese millet
Legumes:
• Soy
Broadleaved crops:
• Buckwheat

Create a crop rotation for vegetables
that includes good cover crops
1. Figure out how much area is needed for each major crop
(the ones needing the largest amount of space).
2. Measure and map the land available
3. Divide into equal plots big enough for the major crops
4. Group compatible crops together to fill each plot
5. Set a good sequence, maximizing cover crop
opportunities
6. Include best possible cover crops at every opportunity
7. Try it for one year, then make improvements
For all the details, see my slideshow
Crop Rotations for Vegetables and Cover Crops on
SlideShare.net

Winter cover crops at Twin Oaks
1. Winterkilled cover crops
2. Under-sowing
3. Wheat and Rye – hardy grasses
4. No-till cover crops
5. Including winter-hardy legumes
Rye, crimson
clover, winter
peas. Photo
Bridget
Aleshire

1. Winterkilled Cover Crops - oats
 Winter-killed cover crops
smother weeds and grow
biomass to provide a dead
mulch to cover the soil and
hold it in place until early
spring. The dead material is
more easily incorporated in
spring than a green cover crop,
making the soil ready for
planting earlier.
 We sow oats in the areas
where we plan to plant the
early spring crops next year.
 Needs a crop rotation that
clears those patches before the
end of the previous August.
AFTER GROWING
early sweet corn,
spring broccoli,
cabbage and
spring-planted
potatoes
Sow OATS in
August
NEXT YEAR, PLANT
peas, cabbage,
broccoli, carrots,
March-planted
potatoes, spinach
and the first sweet
corn

When to sow oats for a Winter
Cover Crop
 5-8 weeks before your
average first frost to get
good size plants before they
get winter-killed.
 For us, that’s 8/5-9/17 (our
average first frost is 10/14).
 If sown too early, oats head
up in the fall and even drop
seed.
 If sown too late, they won’t
provide much biomass
before they are killed.
 A 2 week delay in sowing can
seriously reduce the
effectiveness of the cover
crop
Photo Oklahoma Farm Report

About Oats
 Low-cost, easy to establish, fast-growing - provided the
temperatures are right - minimum soil temperature for
germination is 38F (3C)
 Grow to a height of 2-4 feet (0.6-1.2 m) if not killed before
then.
 Will grow in a wide pH range, and even do OK in poor soils
 If sown in August/early September, reliably winterkill in
zone 7a - average annual minimum temperature range 0-5F
(-18C to -15C).
 Seedlings die at 17°F.
 Large oat plants will get serious cold damage at any
temperature lower than about 20F (-7C) and will die
completely at 6F (-17C) or even milder than that.

Benefits of Oats
 If they die, they are simple to till in; if they don’t
die, they are still easy.
 Some tolerance to flooding
 Add lots of biomass
 Very good at shading out germinating weeds
 Very good at salvaging any nutrients (especially nitrogen)
left from the previous crop and making them available to
the following crop.
 Oats increase the biological activity of the soil, reduce
soil erosion (their fibrous roots anchor the soil) and
absorb and store rainfall.

Limitations of oats as a cover crop
o Oats are not as good at breaking up compacted subsoil as
some cover crops, but they do loosen the topsoil nicely.
o Less allelopathic effect than winter rye. I suspect that if the
crop is winter-killed, little allelopathy remains in the spring.
o Not much tolerance to heat or drought (more than rye).
o Oats do not add nitrogen, but often you can add a
nitrogen-producing legume in with the oats.
o Unlike flowering cover crops, they do not attract beneficial
insects (assuming they are winter-killed before heading up
and shedding pollen).
o Beware GMO canola from feed store “horse oats.” You
don’t want GMO canola going feral! Buy organic!
o Spring oats can be sown in late summer, early fall or early
spring.

Other Winterkilled Cover Crops
During August and September, other
warm-weather cover crops can be used
for areas that will be planted early the
next year:
1. Frost-tender sorghum-sudangrass
hybrid, buckwheat, soy, cowpeas,
Miami peas, sunnhemp and millets.
2. Crops which winter-kill at 5-20°F
include oats, barley, berseem
clover, Lana vetch, purple vetch,
fava beans, Canadian/spring field
peas, oil and fodder radish.
They can be used before early spring
food crops.
Sorghum sudangrass hybrid.
Photo by Bridget Aleshire

2. Under-sowing (inter-seeding) for
more winter-killed cover crops
• Want more areas in winter-killed cover crops? Under-sow. (Most of our
food crops are not finished in August.)
• Cultivate the food crop in August 2 weeks after planting.
• Repeat after 2 more weeks and sow cover crop between the rows of
the vegetable crop while it is growing.
• Remember to irrigate if nature doesn’t. The food crop will have good
roots by then, but the cover crop seed will be just below the surface
and will need some help to germinate.
• The cover crop continues to grow after the food crop is finished - you
have your winter cover crop in place early and you don’t need to invert
the soil again.
Sweet corn under-
sown with soy.
Kathryn Simmons

Example of undersowing oats
• We undersow our 6th sweet corn (sown 7/16) 4 weeks
after seeding, with oats and soy in mid-August, a perfect
time for oats.
• Soybeans are also winter-killed in our climate, so they
make a good companion for the oats.
• Oats and soy are both somewhat shade-tolerant.
• They also tolerate foot-traffic when it’s time to harvest.
• It’s important not to till between rows of large food crop
plants – it damages their roots. With corn, it’s wise not to
till after the crop is knee-high.
• We do not mow down the corn after harvest, but just leave
it until early spring. It incorporates pretty easily by then.
• We follow this combination with our spring potatoes,
planted mid-March.

(Under-sow summer cover crops too!)
• Buckwheat or white clover can be under-sown in a
spring vegetable crop, to take over after the food
crop is finished.
• Buckwheat can be undersown in winter squash,
watermelon or sweet potatoes, and mowed or tilled as
soon as the vines start to run. Once we tried buckwheat
between our squash rows to keep the weeds down, but
failed to mow or till it in, and had to wade in and pull it by
hand.
• One trial of undersowing buckwheat in corn reported that
if sown the same day as the corn, the buckwheat
outcompeted the crop; if sown at the eight-leaf stage of the
corn, the buckwheat did not get enough light.

Green fallow at Twin Oaks
• Full year cover crops (green
fallow) can build soil fertility.
• We discovered a “spare” plot!
• In August, we under-sow our fall
brassicas with a clover mix - to
form a green fallow crop for the
whole of the following year, to
replenish the soil and reduce
annual weeds.
• 2 weeks after transplanting the
brassicas (August), we hoe and till
between the rows, or wheelhoe.
We repeat at 4 weeks after
transplanting.
• Then (late August-early
September), we broadcast a mix
of clovers
Clover green fallow in July.
Photo by Bridget Aleshire

Clover fallow details
• 1 oz crimson clover, 1 oz Ladino white clover and
2 oz medium red clover per 100 sq ft.
• Crimson clover is the fastest growing in the fall,
and the others gradually take over in the spring
and summer of the next year.
• White clover: 3 main types - the large (12-15”)
type, Ladino, produces the most biomass and
the most N. It is not as durable or as heat-
tolerant as the intermediate types, and is later
to flower. The lowest growing type (Wild White)
is used for high traffic areas like orchard alleys;
the intermediate-height range (up to 12”)
includes Dutch White and New Zealand White.
• Red clover: get medium, multi-cut red. Don’t
use mammoth if you want to mow regularly.
• Don’t till the seed in. Use overhead irrigation to
get the clover germinated - aim to keep the soil
surface damp for the few days until germination.
Usually watering every two days is enough.
Broccoli with clover under-sown.
Photo Nina Gentle

Green Fallow Decision Points
We plan to keep the clover growing for the whole next year. Back-up plan:
• In spring, we bush hog the old brassica stumps and let the clover flourish.
• If the plot is not too weedy, we keep the clover, mowing once a month or so
to prevent the crimson clover and the annual weeds from seeding. I have
often been surprised at how a patch that is thin and weedy in March and
April can look really good by May, and lush by the end of June.
• In late April, we assess again. If there are too many perennial weeds, or the
clover isn’t growing well enough, we disk and plant warm weather covers,
(buckwheat, soy, sorghum-sudangrass hybrid) until frost.
• In July, if the weeds are bad we disk in the clovers and sow sorghum-
sudangrass mixed with soy. While this deals effectively with the weeds, it is
a poor crop rotation, as the next year’s crop in that patch is early sweet
corn, which is related to sorghum-sudan.
• In August, if the weeds are gaining the upper hand, we disk and sow oats
(perhaps mixed with soy). If the clover is still growing well (as it usually is),
we leave the green fallow to overwinter.
• We disk it in February, a year and a half after sowing, for early sweet corn.

Keys to success with undersowing
• Timing is critical: Sow the cover crop late enough to
minimize competition with the food crop, but early
enough so it gets enough light to grow enough to
endure foot traffic when the food crop is harvested.
• The leaf canopy of the food crop should not yet be closed.
Often the best time is at the last cultivation. With vining
food crops, it’s important to sow the cover crop before the
vines run.
• Choose vigorous food crops, but cover crops that are only
moderately vigorous. Buckwheat, millets and cowpeas all
have their fans for summer use.
• Ensure the seedbed is clean and the soil crumbs small
enough.
• Use a high seeding rate, whether broadcasting or drilling.
• Irrigate sufficiently.

Location, location, location
Some things that work in New York state don’t work in Virginia
• Kale undersown with rye and hairy vetch, rye alone, or oats in
mid-late August
– in Virginia, winter rye sown in August goes to seed the same
year.
– we overwinter kale, and cover crops would compete too much.
• Winter squash and pumpkins undersown with red or crimson
clover when the vines are just starting to run.
– in central Virginia this was a hopeless failure - the vines grew so
much faster than the clover and smothered it.
• Sweet corn undersown with crimson clover:
– In the South, corn grows too fast compared to clover.
– It is difficult in Virginia to get the clover to germinate in the
heat and dryness of June and July. Soy is easier and cheaper.

3. Winter wheat
Winter wheat. Photo USDA
Winter wheat prevents erosion
suppresses weeds
scavenges excess nutrients
adds organic matter
less likely than barley or rye to become
a weed
is easier to kill than barley or rye
cheaper than rye
easier to manage in spring than rye
(less bulk, slower to go to seed)
fine root system improves tilth
tolerates poorly drained, heavier soils
better than barley or oats
Can be sown in spring – it will not head
up, but “wimps out”
 encourages helpful soil microorganisms
Challenges
o Not good tolerance of
flooding
o a little more susceptible
than rye or oats to insects
and disease

Winter Rye/Cereal Rye
 Rye grows 5-7' tall.
 Mow-kills at flowering, but not earlier.
 Suppresses weeds (especially lambsquarters,
redroot pigweed, ragweed).
 Sow from 14 days before to 28 days after first fall
frost, but makes little growth in mid-winter
 Rye can be sown in the spring, although oats
break down quicker.
 Don’t sow in August in zone 7 – it may set seed.
 Can be undersown in sweet corn or in fall
brassicas in early September, and left as a winter
cover crop.
 Rye needs 3-4 weeks after tilling in, in spring, to
break down and to disarm the allelopathic
compounds that stop small seeds germinating.
Kauffman Seeds

Cover Crops for Fall
September
Before 9/15, oats
Any time in September:
winter rye, winter
wheat, winter barley,
hairy vetch, crimson
clover, red clover,
Austrian winter peas.
October
Before 10/14, winter
wheat with crimson
clover or red clover.
After 10/15, winter
wheat or winter rye
with Austrian winter
peas
November
Before 11/8, winter
wheat or winter rye,
Austrian winter peas
From 11/9 to 11/15 (a
month past our average
frost date) winter rye
alone
Only include legumes if there will be time in spring for them to flower

4. Organic no-till cover crops
Kill the cover crop without tilling, and plant food crops
into the dying residue.
3 ways to kill cover crops without herbicides
1. Winter-killed cover crops for early spring food crops
2. Mow-killed cover crops.
3. Roll-killing is another option, but usually requires
special equipment.
Photo Rye, hairy vetch, crimson clover. Kathryn Simmons

Organic no-till benefits to the soil
 Soil is kept covered, reducing erosion.
 Soil compaction is reduced by having fewer tractor passes.
 Soil layers are not inverted, the soil micro-organism habitat
is undisturbed, the root channels of the cover crops are
undisturbed, and the number of earthworms and microbes
increases.
 Soil structure improves, organic matter increases and the
cover crop biomass is conserved, rather than burning up as
quickly as it would if incorporated.
 Soil can absorb and retain more water, making it more
resilient in drought. Yields are higher under drought
conditions than on tilled soil.
 Soil retains cooler temperatures into the summer, increasing
root growth.

Other organic no-till benefits
 Reduced use of agricultural plastics.
 If spring is wet, it may be possible to mow, when you couldn’t till.
 Fewer tractor passes - labor, fuel and machinery costs are reduced.
 No new weed seeds are brought to the surface.
 Some pathogens and pests may be suppressed.
 Mulch grows in situ – no need to haul and spread.
 Crops such as pumpkins are cleaner than those grown on bare soil.
 Legumes in the mix can provide all the nitrogen the next crop needs.
The cost of N from vetch seed is half the cost of N from fertilizers.
 Legumes are a slow-release fertilizer: 15% of the nitrogen in the vetch
is in the roots, in position in the soil for the new transplants. 50%
becomes available to the food crop as the soil warms in spring and
early summer; 50% remains for the following season.
 Hairy vetch activates plant genes that increase disease tolerance and
plant longevity, giving tomatoes an extra 2 to 3 weeks of production

Suitable cover crops for no-till
Which winter annual cover crops to choose ? Consider cold-
tolerance, the length of the growing season, and efficacy in
fixing nitrogen and producing biomass. Do you want a winter-
killed cover crop (oats, sorghum-sudangrass) or a hardy one
(winter wheat or winter rye)?
Using a mixture of grasses and legumes helps limit the loss of
N from the cover crop through leaching or denitrification.
Generally, use a grass/legume mix in a 2:1 ratio, although
you can use higher amounts of legumes, up to 1:1. Hairy
Vetch, Austrian Winter Peas, Crimson Clover
There are advantages to including more than one legume in
the mix – in unusual weather, one may struggle, while the
other does better.

No-till cover crops for
early spring vegetables
• Frost-tender cover crops can be used before early
spring no-till food crops. It is best to mow or roll
the cover crop at around the first frost date, to
provide a more uniform mulch in the spring. Weeds
may be a problem and the soil will be colder than
bare soil — this may work for cabbage and broccoli.
• For the very earliest spring crops, forage radish
lab-lab bean or bell beans will die back and leave
almost bare soil. While still growing, they suppress
weeds.
• BUT fast-maturing spring vegetables will not do
well with no-till cover crops unless you add N
fertilizer, as they need nitrogen more quickly than
can be got from no-till.

No-till cover crops before
late spring vegetables
No-till cover crops are grown to flowering, killed by mowing
or rolling, and left to become mulch for the next crop.
 A 1994 USDA trial of various no-till cover crop mulches for
tomatoes found that hairy vetch (without added nitrogen
fertilizer, and without any weeding)
out-yielded plastic-and-fertilizer plots
by about 25%, and out-yielded
fertilized bare soil by 100%.
 We have 1 year in 10 as a no-till year.
We use no-till cover crops for our Roma paste tomatoes,
which are transplanted in early May. We don’t need early-
ripening for these, making them a good no-till food crop.

Suitable food crops for no-till
• Late-spring transplanted crops such as late
tomatoes, peppers, eggplant, Halloween
pumpkins, or successions of cucumbers
and squash can do very well after a winter-
hardy legume-grass mix no-till cover crop.
• I have read that transplanting eggplant into crimson
clover (sown in the fall before) will reduce flea beetle
outbreaks, but I have yet to try it. Mowing after early
bud stage will kill crimson clover.
• If you have machinery or hand tools for seeding into
no-till cover crops, direct seeded crops are possible.
• At the Coastal Plain Experiment Station in Tifton,
Georgia, they are trying peanuts planted into crimson
clover.

Steps of mow-killed no-till cover crops
1. Find a plot available in early
September: Our spring broccoli
and cabbage finish in early July.
We follow them with a round of
buckwheat summer cover crop.
2. Then, on September 7–14, we
sow winter rye, Austrian
winter peas and hairy vetch.
Austrian winter peas are said
to reduce the incidence of
Septoria leaf spot in following
tomato crops, so we include
those. 1.5 oz HV, 1.5 oz AWP,
2.5 oz Rye per 100 sq ft
Winter rye, hairy vetch and Austrian
winter peas.
Photo Bridget Aleshire

Mow-killed no-till steps continued
3. Grow a solid stand of a cover
crop for high biomass. The goal
is to have the vetch be about
4” tall before hard frosts of
22°F stop growth.
4. The next year we do not till in
this cover crop but mow it very
close to the ground using our
hay mower (5/1-5/5), just
before our transplanting date.
5. This kills the cover crops. If
mowed too early, they will not
die. The vetch should be
flowering. Rye should be at the
soft dough stage - bite a kernel.Winter rye and hairy vetch. Photo
Kathryn Simmons

Mow-killed no-till continued
6. Plant the food crop into
the dying mulch with as
little disturbance of the
cover crop as possible.
Transplant, or seed
using equipment to
open a narrow slot
deep enough for the
seeds. We transplant
paste tomatoes.
7. The dead mulch keeps
weeds away for 6 -10
weeks in our climate.Flowering hairy vetch with rye at
mowing stage. Photo by Bridget
Aleshire

No-till cover crops continued
8. The vetch and peas (if plentiful) supply all the nitrogen
the tomatoes need.
9. In our humid climate the no-till mulch does biodegrade.
In July we roll hay between the rows, to top up the
mulch. We plant the tomato rows 5.5 feet apart and the
plants are staked and woven, so we can snugly fit big
round bales of hay down the aisles.

Cautions about no-till planting
o Cold-hardy cover crops need time in spring to grow to
optimal size before mowing - not suitable for early
spring food crops
o Untilled soil in spring is colder than tilled soil, and
growth of anything you plant in it will be slower, and
harvests delayed. Not good for watermelons!
o Transplanting into untilled soil is harder work than
planting into loose tilled soil.
o Hand-seeding into untilled soil is tricky – winter
snow and ice can leave soil quite compacted.
Unsuitable for small seeded, closely-spaced
vegetables.
o Initial hopes for no-till cover crops - that it would be
possible to grow vegetables organically without ever
tilling again - were unrealistically high.

Challenges with organic no-till
• The timing of sowing, rolling or mowing and planting
is critical. The wrong weather can jinx your plans.
o If the cover crop stand is poor, weeds will germinate – have a
Plan B. Usually this will involve tilling, adding compost and
then finding another mulch.
o There may be some regrowth of the cover crop, if mowing
was too high, irregular or poorly timed. If needed, mow
between the crop rows a couple of weeks later.
o There may be more fungal diseases and slugs.
o In arid zones, it is necessary to wet the mulch weekly to
release the nutrients. Drip irrigation won’t do that.
o The rate of nitrogen release from the cover crop will be
slower than from an incorporated cover crop.

No-till tractor equipment
• For mowing cover crops, we use our hay mower/conditioner rather than our
(rotary) bush-hog, as it cuts close to the ground and lays the cover crop down
without chopping it into small pieces. This helps it last longer, and be easier to
transplant into. Flail-mowers are recommended over lower-speed sickle-bar
mowers, which can get tangled with long vetch vines.
• Roll-killing leaves a longer-persisting mulch than mowing, although there may
be problems with re-growth. Adding a method of crimping the stems increases
the effectiveness. Hairy vetch is harder to kill by rolling than crimson clover.
• Ron Morse designed a No-Till Planting Aid, consisting of a heavy coulter and
shank assembly with a wavy coulter behind the shank to slice the mulch and
leave a 2-3” strip of prepared soil, for planting in a separate operation.
• Transplanters are available that are designed for use with thick organic
mulches.
• No-till seeders are harder to find: an example has a toolbar planter, 15” fluted
disk blades to cut through the vetch mat, 15” double disk opener, 12” cast-iron
closing disks, plastic seed pressers and extra weights.

5. Including winter-hardy legumes
Crimson clover flower,
Photo Kathryn Simmons
For maximum N, mow and
incorporate cover crops when
they start to flower.
A good legume stand can provide
all the N the following crop will
need. We only spread compost
for our late crops if we had poor
luck with the legumes.
Include legumes in cover crop
mixes whenever possible, to add
nitrogen to the soil.
Austrian winter peas can be sown
later than clovers.

Hairy Vetch
Very widely-adapted, cold-hardy to
−15°F
Needs a minimum soil temperature of
60°F to germinate
Sow 40-60 days before the first 28°F
frost
Grows quickly in fall
In spring it reaches a height of 2' alone
or 6' if mixed with tall cover crops.
In zone 7, 9/7–10/10 is ideal for sowing.
Don’t delay - over 1100 Growing Degree
Days are required in the fall to make
enough growth.
Hairy vetch and winter rye.
Photo by Kathryn Simmons

Hairy Vetch Benefits and Challenges
Benefits:
 Drought tolerant once
established.
 Suppresses yellow nutsedge,
lambsquarters.
Challenges:
o Vines can be tangly.
o Can be invasive if it sets seed.
o Seed is poisonous to poultry.
o May harbor pest nematodes.
o Not tolerant of shade or
flooding.
Hairy vetch
Photo Southern Exposure Seed Exchange

Clovers
 Many types of clover - used to
discourage weeds, add nitrogen and
biomass to the soil and prevent erosion.
 Clovers attract beneficial insects and
reduce aphids.
 Main uses : as overwinter cover crops;
green fallow (full year cover crops);
under-sown in existing food crops, no-
till or reduced-till crop sowings in
standing clover.
 Best planted with a grass crop. Alone
they sprawl.
 “Frost Seeding” - broadcast clover seed
on prepared soil, early in the morning
after a hard frost. The thawing will wet
the seeds and pull them down into the
soil. (2/15-3/15 in central Virginia).
Field of crimson clover.
Photo Bridget Aleshire

Crimson
Clover
 Deep-rooting annual, hardy to 0°F (-18°C).
 In zone 7, 9/1–10/14 is ideal time to sow.
 Establishes earlier than hairy vetch in fall, so
suppresses weeds better.
 Fall-sown crops make fast growth in spring
 Grows to 18" or 36”with a supporting crop.
 Flowers a few weeks earlier than hairy vetch.
 Mow at early bloom (in central Virginia 4/16-
5/2, most usually around 4/20).
 Provides about 2/3 as much N as hairy vetch.
 Can also be sown in very early spring, but will
not make much growth before flowering (in our
climate at least).
 Benefits: Shade tolerant. Attracts beneficials,
including assassin bugs which eat Colorado
potato beetle. Suppresses Italian ryegrass. Can
be undersown in fall crops for winter cover.
Crimson clover, Photo
Kathryn Simmons

Over-winter crimson clover
in our rotation
sweet corn,
June-planted
potatoes,
watermelons
and sometimes
tomatoes and
peppers
Crimson Clover
sown 9/20-
10/15, with
wheat. Turned
under in late
April
Later corn
plantings,
winter squash,
transplanted
watermelon,
tomatoes,
peppers, sweet
potatoes, June-
planted
potatoes, fall
brassicas
Vegetable
crops cleared
by end of
September/
mid October
Vegetable
crops
planted after
late April
Photo Crimson clover
Bridget Aleshire

White clovers
 Perennials used as winter annuals in the South.
 Hardy to −20°F. Generally hardier than red clovers, and smaller.
 Can be frost-seeded in early spring
 Or sow in fall, at least 6 weeks before a hard frost.
 Only sow in summer if you can keep the soil damp.
 Water frequently until established.
 Competes poorly with weeds until well established.
 Good for all-year cover, tolerates foot traffic. Drought tolerant.
 Has stolons, so good at re-growing after mowing.
 The dwarf type is not a good choice to mix with grasses.
White clover.

Red clovers
 Short-lived perennials.
 Cheap. Best incorporated after a full season
of growth (needs time to grow - 24-36” tall)
 Good weed suppression.
 Tolerates shade and poor drainage (not
flooding).
 Fairly cold tolerant (not as hardy as white
clover).
 Attracts beneficial insects.
 In the S, sow in fall or spring, 30 days before
first fall frost, and 30 days before last spring
frost. In the N, from 45 days before last frost,
up till 30 days before first frost. In warmer
weather, sow with a nurse crop (rye,
buckwheat or oats). Ensure sufficient water.
 Mammoth is easier to establish in dry soils
than Medium, faster growing, bulkier, but
not good at re-growing after mowing.

Subterranean clover (Sub clover)
 Re-seeding cool season annual.
 Best suited to areas with dry summers, mild wet winters.
 Thick, low growth, good for long-term orchard floors, living
or dying mulch, erosion control.
 Survives close mowing.
 Strong seedlings, good weed suppression.
 Dormant in winter, regrows in spring.
 Seeds, then dies in summer.
 New plants germinate in the fall.
 In hardiness zone 7 and warmer, sow in the fall. In colder
zones, sow in spring.

Berseem clover/Egyptian clover
 (Bigbee, Multicut), grows 24” tall. Very productive, vigorous annual
white clover.
 Does best in hot moist conditions, tolerates wet soil.
 Mow to 3", not less, when 7–20" tall.
 Excellent weed suppression.
 Sow in spring, or late summer if water is adequate.
 Sow with oats as a winter cover before early spring vegetable crops.
 Frost seeding is not very successful.
 Hardy to 15°F. If it winter-kills, it leaves a friable seedbed needing
minimal spring tillage, if any.
 Oats and berseem clover have a good write-up in Managing Cover
Crops Profitably.

Sweet clover
 Grows up to 6ft tall.
 White Hubam variety is an annual, winter-kills at 19°F.
 Other sweet clovers are biennial.
 Yellow sweet clover is not easy with small scale equipment, and can
be difficult to incorporate. (White is much easier.)
 The yellow is earlier than the white, but less productive.
 Yellow sweet clover seed is cheap, white is expensive.
 Mow high for maintenance, e.g., if inter-seeded between crop
rows.
 Deep rooted.
 Requires 17" of water per season.
 Sow late summer for heavy growth next spring.
 Spring sowings make growth by early summer.
 Can be frost-seeded in late winter.

Cautions with clovers
o Clovers do not winter-kill in our zone 7 climate.
o Consider avoiding legume cover crops ahead of legume food crops,
to reduce the likelihood of spreading pests or diseases. We haven’t
seen any problem that we can directly blame on a poor rotation,
and until that happens we’ll likely continue to add legumes
frequently, to increase the soil organic matter, feed the soil
microorganisms and support the nutrient cycle.
o Beware red and crimson clovers, (and some peas and beans, beets,
buckwheat) before white potatoes, as these can host Rhizoctonia
and scab.

Austrian Winter Peas– a cold-hardy
leguminous cover crop
 Hardy type of Field Pea. (Black peas)
 Winter-kill in zone 6, hardy in zone 7. Hardy
to 0F (-18C). (Canadian/spring field peas are
hardy to 10-20F (-12 to -7C)).
 Can sow several weeks later than clovers
 Sow at least 35 days before first hard freeze
- in zone 7, 8/10–10/24 (11/8 OK)
 Optimum temperature for germination is
75F, minimum germination temperature 41F.
 Good at emerging through crusted soil
 Tolerate a wide range of soil types
 Make rapid spring growth in cool weather
 Suppress weeds, prevent erosion
Austrian winter peas

Benefits of Austrian Winter Peas
Austrian winter peas with
winter rye. Photo Cindy
Conner
 High N-fixers - a good stand can provide enough
N for the following food crop when
incorporated.
 As much, or more, than crimson clover
 More dry matter than hairy vetch (which
produces more than crimson clover) in the SE.
 Can be mixed with grasses for vertical support,
more biomass and better weed suppression.
 Suppresses Septoria leaf spot in tomato.
 Blooms late April at Twin Oaks, before hairy
vetch
 Flowers attract beneficial insects (especially
honeybees) and reduce aphids.
 The tendrils and shoot tips make a nice addition
to salads or stir-fries in the spring.

Austrian Winter Peas in our rotation
Latefinishingcrops
winter squash,
melons, sweet
potatoes,
tomatoes,
peppers,
middle sweet
corn, June-
planted
potatoes
Sow
Austrian
Winter Peas
Oct 1-Nov 7
With winter
wheat or rye
CropsafterMay1st
winter squash,
melons, sweet
potatoes,
tomatoes,
peppers,
middle sweet
corn, June-
planted
potatoes
Photo by Cindy Conner

Cautions for Austrian Winter Peas
o Pea seed cannot be stored long. The germination
rate could be only 50% after 2 years. Run a
germination test if you have seed you are unsure
about.
o Seeds are large and heavy - high sowing rates
(compared to clovers). Cost/area is fairly high, a
little higher than vetches
o If you haven’t grown peas or beans on that plot for
some years, inoculate the seed.
o Winter-killed in zone 6, at 0°F. For the best chance
of winter survival in cold areas, choose your
sowing date to get plants 6-8” tall before the soil
freezes. (Hairy vetch is more cold-tolerant than
AWP.)
o Sowing in a mix with a winter grain will improve
cold weather survival by reducing soil freezing and
heaving.

When Austrian Winter Peas are
unsuitable.
o May not do well if sown in spring - require a cold dormant spell.
o Not tolerant of flooding, drought, high traffic, salinity, heavy
shade, long cold spring weather below 18°F with no snow
cover, or hot (or even warm) weather.
o Do not regrow after mowing or grazing once blooming starts.
o Peas on their own do not add much organic matter to the soil -
the vines break down quickly.
o May increase 39 species of pest nematodes, so if you are
already having trouble with those, this is not a good cover crop
for you.
o Susceptible to Sclerotinia crown rot, which can completely
destroy crops during winter in the mid-Atlantic. One reason not
to grow pea crops on the same land two years running.
o Can also be host to Sclerotinia minor, Fusarium root rot and
Ascochyta blight.

Early spring cover crops we
use at Twin Oaks
 In February or March we sow oats, where we have winter weeds,
no cover crop, and will not be planting a food crop for 8 weeks.
That is sufficient time for growth to out-compete weeds and add
to the organic matter in the soil.
 March 31 here is too late in spring for oats (they will quickly head
up after making very little growth)
 In late March or April, we can sow winter rye, which “languishes”
here once it gets hot. One year when our spring potatoes got
flooded we transplanted potatoes to the drier end of the patch
and sowed rye in the lower end, once the floods had subsided.
This kept the soil covered, and was easy to deal with in July at
potato harvest time.
 In early April, too late for oats, but too soon to sow frost-tender
cover crops, we might just till and make stale seed beds (till 2 or
more weeks ahead of time, prepare beds, hoe once a week to kill
weeds)

Late spring and summer cover
crops at Twin Oaks
 In late April (close to our average last frost), we sow frost-tender
cover crops like buckwheat or soy, mixed with a grain such as winter
rye or wheat for insurance and some shielding from harsh weather.
 When summer gaps occur between the end of one vegetable crop
and the planting of the next, we sow a short-term cover crop
 After our corn planting date, if a food crop fails, or we “discover”
some space, we grow sorghum-sudangrass for the remainder of the
warm season.
 Unlike our winter cover crops, we often only plant summer cover
crops in small areas each time, so we broadcast and
till-in with our walk-behind BCS tiller.
Buckwheat flowers.
Photo NRCS

Sorghum-sudangrass
 Fantastic summer cover crop
 Huge amounts of biomass
 Very good at smothering weeds
 Sow during corn-planting season
 Takes 60-70 days to full height
 When it reaches 4-5 ft (1.5m) tall,
mow to a foot (30cm) high, and let
regrow
 Some of the roots die to balance
the needs of reduced top growth,
leaving channels in the soil
 The tops regrow and new roots
grow – improving soil texture
 Dies with frost
 Allelopathy inhibits germination of
small seeds, such as weeds.
o Does need large machinery
Sorghum-sudangrass shown here after
mowing.

Meet the Millets
German foxtail millet
grows to 3'–4' (1–1.3 m),
Japanese millet to 3'–5'
(1–1.6 m)
Pearl millet gets much
taller, at 5'–10' (1.6–3.2 m).
Of the millets, pearl millet
and German foxtail millet
will mow-kill after heading
(not before), but Japanese
and browntop millets will
not reliably mow-kill.
Pearl Millet Non-copyrightable image
courtesy of the USDA-ARS

Warm weather legumes - soy beans
• Soy has been a handy legume for
us, because Twin Oaks has an
organic tofu business. We can get
organic beans at wholesale price.
• Almost all non-organic soy grown
in the US is genetically modified, so
if you don’t want to add to the
problems caused by GMOs, buy
organic, or if you are not certified
organic, Identity Preserved.
• See the Organic and Non-GMO
Sourcebook for a searchable
database of non-GMO suppliers.
Sweet corn with undersown soy
cover crop. Photo Kathryn
Simmons

Warm weather legumes - cowpeas
• Most cowpea varieties
mature in 60-90 days and
will be killed by the first
frost. (Oats may provide
temporary protection).
• Iron and Clay cowpeas are
often used to break up
compacted soil
Iron and Clay Cowpea. Photo Southern
Exposure Seed Exchange

No-till cover crops for fall vegetables
For fall vegetables such as broccoli, (and
winter vegetables in hot climates):
• A mix of soybeans or cowpeas and
foxtail millet can be grown over the
summer and mow-killed before
planting.
• Frost-killed Sorghum-sudangrass and
sunnhemp could also work. (Beware
allelopathy of sorghum-sudangrass)
Foxtail millet

About Buckwheat
This warm-season broadleaf annual germinates in just a
few days,
Takes only 30-50 days to grow to full size - a height of 2-3'
Sow from around the last frost date to late summer (50
days before first frost).
Incorporate 7-10 days after it starts flowering.
A useful cover crop in case of crop failure or early end of a
food crop.
Buckwheat flower.
Photo NRCS

More about Buckwheat
Use to prepare land for perennials or to bring
neglected land back into production.
• Till the field, up to 2 weeks before the last
frost,
• Cultivate after 10-14 days to kill new weeds.
• Sow buckwheat thickly, let it flower and seed
(8 weeks). Sow early to reduce winter weeds
• Till again, let the volunteers grow, to reduce
warm-weather weeds.
• Either incorporate in the fall or let the
buckwheat frost-kill
• If for perennials, plant in late winter or early
next spring
• If reclaiming neglected land, sow winter cover
crops into the bare soil or no-till drill into the
dead buckwheat.
Young asparagus patch with self-
sown buckwheat “weeds”.

Benefits of Buckwheat
 Can be left to self-seed if there is time for several
sequential plantings of buckwheat. (Cheaper than buying
more seed.)
 If the soil is too wet to disk or till, it can be mow-killed or
rolled.
 Almost 3 times as good as barley in scavenging phosphorus,
and more than ten times better than rye (a poor
Phosphorus scavenger).
 Not related to any of the common
food crops - simple to include in
rotations.
 Quick to incorporate, easy with
manual or small-scale equipment.
Photo NRCS

Strengths of Buckwheat
Buckwheat does a good job of suppressing weeds,
especially ragweed and purslane.
Improves the soil tilth (aggregate structure) with its
fibrous roots, and extracting K, Ca and P from the soil
Mowing will kill buckwheat in full flower, but non-
flowering plants may re-grow from lower nodes.
Open-faced flowers attract many beneficial insects
including honeybees, hoverflies, lady beetles;
caterpillar-predatory wasps and tachinid flies; aphid and
mite predators; minute pirate bugs and insidious flower
bugs (which feed on small insects and insect eggs such
as corn earworm eggs).
Photo NRCS

Weaknesses of Buckwheat
o No tolerance of frost, drought or flood - seed can rot in
waterlogged soil.
o Little tolerance to salt, shade or compacted soil.
o Only fair at reducing soil compaction and erosion; poor at
scavenging nitrogen.
o The summer weeds most likely to grow in gaps in a stand of
buckwheat are redroot pigweed, lambs-quarters and
barnyard grass.
o Provides relatively little biomass – decomposes fairly quickly
if cut and left on the surface. Thick sowing can overcome this,
but warm weather grasses, forage radish or lupins will
provide more value for money spent on seed.
o May harbor root lesion nematodes (not root knot
nematodes).

Summer Cover Crops in the Hoophouse
• Hoophouse growing burns up the organic matter
in the soil at a fast rate. In summer you could
grow cover crops to replenish the OM, ready for
your next fall plantings.
• Buckwheat, soy, and cowpeas all work well.
• If you don't have harlequin bugs, brassicas may be
a good choice. But if you grow winter greens,
brassica cover crops would be a poor rotation.
• Short term, manageable, fast-growing cover crops
are needed:
– Clovers are too slow.
– Winter cereal grains won't grow in the
summer.
– Beware of huge hot weather grain crops, like
Sorghum-sudan. We grew Sorghum-sudan one
year, and it grew all too well!
– The shorter millets are manageable Buckwheat photo credit Southern
Exposure Seed Exchange

Brassica cover crops for pest control
• We tried a forage brassica
(canola/rape), before a new strawberry
planting, but it encouraged too many
brassica pests, harlequin bugs being
the worst.
• We decided brassica cover crops are
not for us. In areas where they work,
try daikon, forage radish, mustards or
canola. Do this when the soil is 45°F–
85°F (7°C–30°C). That’s up until early
October for us.
• Aim to get 6-8 leaves before a 28°F
frost.
• Brassicas produce allelopathic
compounds that inhibit weeds and
biotoxins (glucosinolates) that kill
pests.Photo Kathryn Simmons

Biofumigation with mustards
When solarized, mustards release volatile compounds very effectively.
Different mustards do different jobs. Mighty Mustard offers 3 varieties:
• Kodiak (Brassica juncea): Suppresses soilborne fungal pathogens and
nematodes, produces more biomass than other varieties
• Pacific Gold (Brassica juncea): Reduces soilborne fungal pathogens,
nematodes
• IdaGold (Sinapis alba): Suppresses weeds. Photo Mighty Mustard

Root Knot Nematodes
• Peanut Root Knot Nematodes popped
up in sections of our hoophouse in
2010-2013.
• 64°F is the threshold soil temperature
for nematode reproduction
• We have grown nematode-
suppressing cover crops, wheat and
white lupins, OP French marigolds,
sesame, from September to June.
• We solarized from June to September
• Our current approach is to have 2
years of resistant crops, followed by 1
year of somewhat-susceptible crops
• Resistant crops: Kale, Yukina Savoy,
other Juncea mustards and radishes in
winter, West Indian gherkins,
Mississippi Silver or Carolina Crowder
cowpeas in summer.
Photo Credit University of Maryland
Plant Diagnostic Laboratory

Cover crop mixes – general points
• Mixes can give the advantages of each of the components.
• A mix of several cover crops species will provide more resilience in
the face of extreme weathers.
• Extension.org recommend first selecting 1-3 cover crop species that
serve your major goals, then identifying “missing services” and
choosing 1 or 2 cover crops that provide this service to add to the
mix. Increase the number of species you mix as you gain
experience. Don’t bedazzle yourself with 57 varieties and fail to
learn anything.
• Mixes can generally be sown at a depth of 1” (2.5 cm), regardless of
seed size. Up to 3” deep will be OK.
• When legumes and grasses are mixed, sow in the grass date range.
• When 2 grasses are mixed, the seeding rate of each is reduced by a
third (not a half),
• Do not reduce the seeding rate of legumes by much in mixtures.
Use at the same rate as a pure stand, or reduce the legume seeding
rate by a maximum of 25%.

Cover crop mixes - specifics
• In mixes with oats, reduce the amount of oats to as little
as 30#/ac (34 kg/ha) so that the highly competitive oats
don’t out-compete the other crops.
• We sometimes use a mix of rye, crimson clover and AWP
if the date is borderline for crimson clover and the
weather uncertain, especially if we have the seed on
hand and don’t want to use it the next year when the
germination rate and seedling vigor will be less good.
• Most mixes include some crops that attract
beneficial insects and some legumes to add
N.

Ingredients for mixes
Spring mixes
• Main ingredients could
be oats and peas, 3
oats:7 peas
• Minor ingredients could
include hairy vetch,
radish, turnips and red
clover.
Summer mixes
• Major ingredients
could include soy,
cowpeas, red clover
and buckwheat.
• Lesser ingredients
could include pearl
millet, proso millet,
radish, turnips,
sunflowers and sunn
hemp.

Nurse and patient mixes
• Oats can also be used in an
August/September sowing as a nurse crop
for a winter legume cover crop, such as
crimson clover.
• Sow the mixed legume and oats, expecting
the oats to die in the winter and the legume
to survive into spring and reach flowering
before terminating it.
• The oats protect the legume plants from
initial chilly temperatures, cover the soil
faster and suppress weeds, and also provide
a scaffold for vining legumes to climb.
• This is a way to get a better stand of clover
than is possible if the clover is sown alone,
because clover is slow-growing and weeds
can take over.
• Buckwheat can work well as a nurse crop to
protect late-fall sowings of winter-hardy
crops in locations where timely frost-killing
of the buckwheat is certain.
• Oats, clover and buckwheat mix

Using manual seeders for small-
scale production
You can use an Earthway-type seeder
for small areas of cover crops;
information about this, including which
plates to use for which crops, can be
found in the VABF Infosheet Seeders:
Using Manually-operated Seeders for
Precision Cover Crop Plantings
Make rows about 6” apart.
 For crimson clover use the #5 (beet) EW plate.
 For other clovers use the #8 (light carrot) plate
 Austrian winter peas need the #14 (pea) plate,
 For winter rye, oats, soybeans, cowpeas and hairy vetch, use
the #22 (beets, okra) plate.

Small scale production
• We broadcast and till in small
areas of cover crops with our
walk-behind BCS tiller.
• For slightly larger areas, a spin
seeder can be used (easier on
the arm than manual
broadcasting). Incorporate the
seed using a rototiller.
• For small vegetable plots, mow
cover crops with a sturdy walk-
behind mower, or use a nylon
line trimmer or scythe for
smaller patches.
• A 30” roller crimper for a walk-
behind BCS 732-948 is available
for around $1000 at Earth Tools
in Kentucky. There are YouTube
videos of it in action.
BCS 722 Photo from Earth Tools BCS

Incorporating Cover Crops into the Soil
• If possible, grow to early bloom for max biomass, and with legumes,
max nitrogen
• Incorporate before plants set seed
• Mow with a rotary mower (eg bush hog) which chops the plants into
small pieces. (Sickle-bar mowers and scythes leave long strawy
plants). On a small scale, use a nylon line weed whip.
• Till shallowly, put cover crop where soil life is most active, not deeper.
• If direct-sowing the next crop, incorporate cover crop (especially
winter rye) 3-4 weeks before sowing date in spring.
A cover crop of rye, hairy vetch and crimson clover. Photo Kathryn Simmons

How available is the Nitrogen?
• The amount of nitrogen that will be available to the next crop
depends on the C:N ratio in the cover crop.
• Soil microbes have a C:N ratio of 10:1. When a cover crop is
incorporated into the soil, they use the C and some of the N to make
more microbes, tying it up until they die - it is not immediately
available to the next crop.
• If the cover crop has a C:N ratio of 50:1 (like sorghum-sudan), the
microbes will need to find extra N to make use of all the C. They will
use N from the soil, tying it up until they die. Hence any crop
following immediately after a high C:N ratio cover crop will need a
different source of nitrogen.
• Legumes have a lower C:N ratio (from 30:1 down to 12:1) and when
they are incorporated, soil N is unlikely to be tied up, so is available
for the next crop. This is explained in the North Carolina Extension
Service Horticulture Information Leaflet 37 cited in the Resources.

Planning for Nitrogen availability
• Incorporate high-C cover crops a few weeks ahead
of planting the following crop. This also allows time
for any cover crop allelopathy to subside.
• If cover crop residues are left on the surface
rather than incorporated, the rate of
decomposition is slowed. Although some N is lost
to the air (denitrification), the increased organic
matter can boost the diversity of microorganisms
at the surface.
• Some of the carbon from cover crops is below the
top 8”(20 cm), where almost all soil data are
collected. Remember the value of the roots!

How to chart your rotation plan
In 1996, inspired by
Eliot Coleman’s New
Organic Grower, we
used cards to represent
each major crop.
We modified Eliot’s
method, and put the
cards in a circle, like a
clock face with “hours,”
and set about
imagining a good
sequence.
Crop rotations are a
cycle, and a circular
design makes more
intuitive sense to us,
than a linear format.
Squash
Corn
Potatoes
Corn
Broccoli
Cabbage
Tomatoes
Water
melon
Corn
Potatoes

Winter
Squash
Late Corn
undersown with
oats (1/2). Sweet
Potatoes (1/2)
March-planted
Potatoes, followed
by fall-planted
broccoli & cabbage,
undersown with
clovers
All-year
Green
Fallow
Early Corn
followed by
fall Garlic
(1/2) and
oats (1/2)
Garlic followed
by Carrots (1/2).
Spring Broccoli
& Cabbage,
then rye &
vetch (1/2)
No-till paste
Tomatoes
Water-
melon
Mid-season
Corn, then rye
& crimson
clover
June-
planted
Potatoes

Having the rotation in a useful format
We drew up our ten year rotation on a piece of
card with a small central disk (naming the plots)
attached by a brass paperclip so it can rotate each
year to show which crops will be planted in which
plots. We call this our Rotation Pinwheel
We are still using the same piece of card we
made in 1996, even though we started our
second ten year sequence in 2006. It has seen
quite a bit of White-Out!
For my book, the publishers’ re-drew it tidily.

Year 1. Winter Squash followed by
Rye and Austrian Winter Peas
• Winter squash are sown
in late May, so there is
time for a legume winter
cover crop to reach
flowering before we need
to prep
• Winter squash finishes on
our farm on Halloween,
early enough to include
Austrian Winter Peas in
the following cover crop
mix with rye
• Photo of butternut squash. Kathryn Simmons

Year 2. Late Sweet Corn
and Sweet Potatoes
• Our last corn sowing and our
sweet potatoes are both planted
late in the season. Having them
share a plot works in terms of
allowing the preceding Austrian
winter pea cover crop to flower.
• Late corn can be under-sown with
oats and soy to provide a winter
cover crop that is easily
incorporated before next spring’s
potato planting.
• The sweet potatoes finish in
October, too late to sow oats
before next year’s spring
potatoes. So we follow the sweet
potatoes with wheat.
Sweet potatoes and late corn. Photo Bridget Aleshire

Year 3. Spring Potatoes Followed by
Fall Brassicas
• The plot is disked in February.
• We harvest the March-
planted potatoes in early July,
till in compost and
immediately transplant our
fall broccoli and cabbage.
• We undersow the fall
brassicas with a mix of clovers
(white, red and crimson)
about a month after
transplanting. This becomes
Year 4’s All Year Green Fallow.
Potatoes emerging in spring. Photo Kathryn
Simmons

Year 4. All Year Green Fallow
The clover sown under the
fall brassicas grows all next
year, if all goes well.
We monitor the success of
the clover mix in March,
May, and August.
If the clover isn’t doing well,
we turn it under and sow
oats or sorghum-sudangrass
depending on the season.
If all goes well, we leave the
clover growing over the
winter.
Fall broccoli under-sown with clovers

Year 5. Early Sweet Corn,
Half Followed by Garlic
• We get two food crops in
year 3 and none in year 4.
The Green Fallow is disked in
March in year 5 to plant our
first sweet corn.
• After the early corn, we sow
oats and divide the plot.
• We mow one half from time
to time until late fall, then
disk and plant garlic in early
November.
Sweet corn under-sown with soybeans.

Year 5-6. Sweet Corn → Oats
→Garlic →Buckwheat →Carrots
A tight rotation:
 We harvest the garlic in June of
year 6, sow buckwheat and soy,
 Then sow fall carrots in late July
or early August.
 We harvest in mid-November,
usually too late for a cover crop.
 That half-plot grows 3 food
crops in 2 years.
 We keep the other half of that
plot for spring broccoli in year 6.
Garlic harvest, Photo Marilyn Rayne Squier

Year 6. Spring Brassicas in the Other
Half.
• The oats are turned under in mid-February.
• Spring broccoli and cabbage can be followed by rye, hairy
vetch and Austrian winter peas sown in early September, in
good time to grow a thick stand for no-till tomatoes in year 7.
Photos Kathryn Simmons

Year 7. Paste Tomatoes and Peppers
• We transplant paste tomatoes and peppers into dead no-
till mulch in early May.
• This crop doesn’t finish till the frost, and we have all the
posts to remove before we can sow a cover crop, so it is
usually rye with Austrian winter peas.

Year 8. Watermelon
• Watermelons are not planted till mid-May, so the Austrian winter
peas have time to flower before we disk the cover crop under in
preparation for planting.
• We have finished with watermelon harvesting by late September,
so we disk and sow wheat or rye with crimson clover for the winter
cover crop. Crimson Sweet watermelon. Photo Nina Gentle

Year 9. Mid-season Sweet Corn
• Mid-season corn is sown in early June. The crimson clover has time
to flower before we disk that plot.
• The corn is finished in time to establish wheat or rye and crimson
clover, which will do well and produce lots of nitrogen and biomass
before we need to plant the June potatoes in year 10.
Three varieties of sweet corn sown on the same day, to extend the harvest.

Year 10. Summer Potatoes
• Our second round of
potatoes are planted in mid-
June, giving the crimson
clover plenty of time to
flower before we need to
disk and plant.
• To combat the heat of
summer, we hill and mulch
the potatoes immediately
after planting.
• They are ready to harvest in
October, and we follow with
wheat or rye and crimson
clover or Austrian winter
peas.
June-planted potatoes. Photo Kathryn
Simmons

Resources - General
 ATTRA attra.ncat.org Many helpful publications
 SARE sare.org -A searchable database of research findings
 SARE Managing Cover Crops Profitably. Buy the book or download the free
pdf from their website sare.org/Learning-Center/Books/Managing-Cover-
Crops-Profitably-3rd-Edition
 SARE Cover Crop Topic Room: No-Till sare.org/Learning-Center/Topic-
Rooms/Cover-Crops/Cover-Crops-No-Till
 SARE Crop Rotations on Organic Farms, A Planning Manual, Charles
Mohler and Sue Ellen Johnson, editors. sare.org/Learning-
Center/Books/Crop-Rotation-on-Organic-Farms Buy or download
 articles.extension.org/organic_production The organic agriculture
community with eXtension. Publications, webinars, videos and trainings.
 Growing Small Farms: growingsmallfarms.ces.ncsu.edu click Farmer
Resources. Debbie Roos keeps this site up to the minute. Click Farm
Planning and Recordkeeping to download Joel Gruver’s spreadsheets.
 VABF www.vabf.org/information-sheets Seeders: Using Manually-operated
Seeders for Precision Cover Crop Plantings by Mark Schonbeck/RonMorse

Resources - Books
 The Market Gardener, Jean-Martin Fortier, New Society Publishers
 The Complete Know and Grow Vegetables, J K A Bleasdale, P J Salter et al.
 Knott’s Handbook for Vegetable Growers, Maynard and Hochmuth. Online at
http://extension.missouri.edu/sare/documents/KnottsHandbook2012.pdf
 The New Seed Starter’s Handbook, Nancy Bubel, Rodale Books
 The New Organic Grower, Eliot Coleman, Chelsea Green
 The Organic Farmer’s Business Handbook, Richard Wiswall, Chelsea Green
 Sustainable Vegetable Production from Start-up to Market, Vern Grubinger,
 Grow a Sustainable Diet: Planning and Growing to Feed Ourselves and the Earth,
DVD/CD set Develop a Sustainable Vegetable Garden Plan Cindy Conner.
 Crop Planning for Organic Vegetable Growers, Daniel Brisebois and Frédéric
Thériault (Canadian Organic Growers www.cog.ca)
 SARE Crop Rotations on Organic Farms, A Planning Manual, Charles Mohler and
Sue Ellen Johnson, editors.
 Northeast Cover Crops Handbook Marianne Sarrantino
 Jeff Moyer Organic No-till Farming http://rodaleinstitute.org/shop/organic-no-till-
farming/

Resources - slideshows
 Many of my presentations are available at www.Slideshare.net. Search for Pam Dawling:
Cold-hardy Winter Vegetables; Crop Planning for Sustainable Vegetable Production; Crop
Rotations for Vegetables and Cover Crops; Fall Vegetable Production; Feed the Soil; Fall and
Winter Hoophouses; Spring and Summer Hoophouses; Succession Planting for Continuous
Vegetable Harvests; Sustainable Farming Practices for New Growers and this presentation
 Planning the Planting of Cover Crops and Cash Crops, Daniel Parson
www.slideshare.net/parsonproduce/southern-sawg
 Cover Crop Innovation by Joel B Gruver www.Slideshare.net
 Cover crops for vegetable cropping systems, Joel Gruver
www.slideshare.net/jbgruver/cover-crops-for-vegetable-crops
 Finding the best fit: cover crops in organic farming systems. Joel Gruver, Some overlap with
previous slideshow. www.slideshare.net/jbgruver/cover-crops-decatur
 http://vabf.files.wordpress.com/2013/02/tom-peterson-farm-planning-for-a-full-market-
season.pdf Tom Peterson Farm Planning for a Full Market Season
 Cultural Practices And Cultivar Selections for Commercial Vegetable Growers Brad Burgefurd
www.slideshare.net/guest6e1a8d60/vegetable-cultural-practices-and-variety-selection
 Conservation Systems Research, USDA-ARS Auburn University, Cover Crops for the
Southeast slideshow https://www.ars.usda.gov/ARSUserFiles/60100500/SlideSets/SS01.pdf
 Impacts of plastic and cover crop mulches
http://www.slideshare.net/greenjeans76/weaver-fieldday-ziegler20120810?from_search=1
 Mark Cain Planning for Your CSA: www.Slideshare.net (search for Crop Planning)

Resources – Cover Crops 1
 CEFS Organic Production: Cover Crops for Organic Farms, https://cefs.ncsu.edu/wp-
content/uploads/covercropsfinaljan2009.pdf?3106e7
 eOrganic Agriculture Resource Area of the eXtension website, Cover Cropping in Organic
Systems http://www.extension.org/pages/59454/cover-cropping-in-organic-farming-
systems#.Uk7Z7CRJOv8. (many useful documents.)
 Extension.org, in the eOrganic section, http://articles.extension.org/pages/72973/making-
the-most-of-mixtures:-considerations-for-winter-cover-crops-in-temperate-climates Making
the Most of Mixtures: Considerations for Winter Cover Crops in Temperate Climates
 USDA/ARS Cover Crop Chart, download at ars.usda.gov/main/docs.htm?docid=20323 The
crop “tiles” can be clicked to access more information about 46 cover crops
 USDA project Multifunctional Cover Crop Cocktails for Organic Systems.
http://agsci.psu.edu/organic/research-and-extension/cover-crop-cocktails
 Sequester soil organic carbon http://news.aces.illinois.edu/news/cover-crops-can-sequester-
soil-organic-carbon
 Mark Schonbeck http://www.carolinafarmstewards.org/wp-content/uploads/2012/12/1-
Schonbeck-Principles-of-Sustainable-Weed-Management-in-Organic-Cropping-Systems.pdf
 See plans by Greg Bowman for a roll-kill roller at http://www.croproller.com/ or build your
own http://www.newfarm.org/depts/notill/features/2006/0506/drawings.shtml
 http://www.extension.org/pages/18526/what-is-organic-no-till-and-is-it-
practical#.Uk7a1iRJOv8 A Sub-surface Tiller-Transplanter designed by Ron Morse.

Resources – Cover Crops 2
 asi.ucdavis.edu/programs/sarep/research-initiatives/are/nutrient-mgmt/cover-crops-
database1 University of California Davis, Cover Crops Database
 Cornell University, Cover Crops for Vegetable Growers, covercrops.cals.cornell.edu
nysaes.cornell.edu/hort/faculty/bjorkman/covercrops
 USDA-ARS Auburn University, Cover Crops for the Southeast (also see Slideshows)
ars.usda.gov/southeast-area/auburn-al/soil-dynamics-research/docs/fact-sheets/
 Rodale Organic No-till roller-crimper http://rodaleinstitute.org/our-work/organic-no-till/
 NCSU Department of Horticultural Sciences Horticulture Information Leaflet 37, Summer
Cover Crops, ces.ncsu.edu/depts/hort/hil/pdf/hil-37.pdf
 In Sustainable Production of Fresh-Market Tomatoes and Other Vegetables with Cover Crop
Mulches, Aref Abdul-Baki and John Teasdale found that rye with hairy vetch and crimson
clover produced 22% more biomass than just rye and hairy vetch.
https://www.ars.usda.gov/ARSUserFiles/oc/np/SustainableTomatoes2007/TomatoPub.pdf
 Cornell Buckwheat Cover Crop Handbook (not organic)
hort.cornell.edu/bjorkman/lab/buck/handbook/main.php
 Buckwheat for Cover Cropping in Organic Farming – eOrganic Agricultural Resource Area of
the eXtension website. extension.org/pages/18572/buckwheat-for-cover-cropping-in-
organic-farming
 tranq3.tranquility.net/~jefferson/Cover%20Crop%20Guides/Buckwheat%20Guide%20Sheet.
pdf Buckwheat Cover Crop Guide – Jefferson Institute
 How to De-hull Buckwheat with the Country Living Mill
http://countrylivinggrainmills.com/grainmill3.html
 Sources for seed: Seven Springs Farm, Floyd, VA, 7springsfarm.com; Lancaster Ag products,
PA, lancasterag.com; Adams Briscoe Seed Co, Jackson, GA, (770) 775-7826

Resources – Crop Planning
 AgSquared online planning software: agsquared.com
 COG-Pro record-keeping software for Certified Organic Farms: cog-pro.com
 Free open-source database crop planning software
code.google.com/p/cropplanning.
 Mother Earth News interactive Vegetable Garden Planner, free for 7 days:
motherearthnews.com/garden-planner. Also as an app:
http://www.motherearthnews.com/grow-planner-gardening-app
 The Twin Oaks Harvest Calendar by Starting Date and by Crop are available
as pdfs on my website in this post:
sustainablemarketfarming.com/2013/11/07/growing-for-market-articles-2/
 Target Harvest Date Calculator: johnnyseeds.com/t-InteractiveTools.aspx
 Jean-Paul Courtens, Roxbury Farm www.roxburyfarm.com. Under the
Information for Farmers tab you’ll find great stuff.
 Mark Cain www.drippingspringsgarden.com under the CSA tab, you can
download their Harvest Schedule. Notebook-based system.

Cover crops for vegetable growers Pam Dawling

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