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 2019

Author of Sustainable Market Farming

and The Year-Round Hoophouse

www.sustainablemarketfarming.com www.facebook.com/SustainableMarketFarming

What’s in this Presentation

A.Five steps of cover crop planning

B.Reliable cover crops on our farm at Twin Oaks in central Virginia

C.Winter cover crops we use

D. Spring & summer cover crops we use

E.Cover crops for pest control

F.Cover crop mixes

G.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

5 steps of cover crop planning 1. Identify your opportunities for cover crops

2. For each opportunity, clarify your cover crop goals

3. Shortlist suitable cover crops

4. Choose cover crops that fit the season

5. Record your decisions and results, and review for possible changes next year.

Crimson clover and bumble bee. Bridget Aleshire

Section A

Step 1 - Cover crop opportunities In fall after food crops, for winter – a good place to start 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.) To replace a crop failure. Year-round cover crops/ green fallow

Photo by Kathryn Simmons

Step 1- Identify one 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

Photo Bridget Aleshire

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 3: 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, southern peas

Add organic matter, improve the soil’s ability to absorb, hold water: bulky grasses and legumes, sorghum-sudangrass, millets, winter rye, velvetbean, southern peas, sweetclover, sunn hemp (Crotalaria)

Increase the biological activity in the soil – use varied mixes Reduce erosion: (good roots) grasses especially rye, barley,

oats; also sweetclover, southern peas, sub clover, Improve the tilth of the soil, the sub-soil structure, soil

drainage: sorghum-sudangrass, sunflower, daikon, sweetclover, crimson clover, alfalfa, lupins, southern peas, 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,

southern peas, soybeans, lentils, sunn hemp.

Attract beneficial insects: (flowers) buckwheat, peas,

beans, clovers, brassicas, phacelia, sunn hemp

Pest control: rye, brassicas, sorghum-sudan, sunn

hemp, white lupins, sesame.

Kill nematodes: Pacific Gold mustard, white lupins,

Iron and Clay southern peas, OP French marigolds,

sesame

Step 4: Choose cover crops for the fall Work back from your farm’s first frost date, to see your options

• 80-120 days before frost - buckwheat, soy, southern peas, Japanese millet, sorghum-sudangrass, or a fast vegetable crop.

• 60-80 days before frost - to frost-kill: buckwheat, sunn hemp, soy, southern peas, Miami peas, Japanese millet, sorghum-sudan; to grow into winter: oats with Austrian winter peas, crimson clover, red clover.

• 40-60 days before frost - to winter-kill: oats with soy beans or Miami peas; to survive the winter: winter barley or wheat with Austrian winter peas, red clover, crimson clover, hairy vetch, fava beans.

• 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 frost date - winter rye/wheat + Austrian winter peas.

• Up to a month past average frost date - still OK to sow winter rye.

Choose cover crops for the 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.

• With 60–70 days, Sorghum-sudangrass, German foxtail millet, pearl millet sunn hemp and some southern peas will mature.

• 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.

Step 5 - Record decisions & results; Review for possible changes next year

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

• Red and White Clovers

• Austrian Winter Peas

Summer cover crops

Grasses:

• Sorghum-sudangrass

• Japanese millet

Legumes:

• Soy

• Southern peas

• Sunn hemp

Broadleaved crops:

• Buckwheat

Section B

Winter cover crops at Twin Oaks 1. Winterkilled cover crops

2. Under-sowing and Green Fallow

3. Hardy grasses – Wheat and Rye

4. No-till cover crops

5. Including winter-hardy legumes

Rye, crimson clover, winter peas. Photo Bridget Aleshire

Section C

Part 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/early September

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.

Seedlings die at 17°F (-8°C). Large oat plants get serious cold

damage at any temperature lower than about 20°F (-7°C)

They will die completely at 6°F (-17°C) or even milder than that.

Photo Oklahoma Farm Report

Benefits & limitations of oats • Easy to till in, dead or alive.

• Some tolerance to flooding

• Add lots of biomass

• Shade out new weeds

• Salvage any nutrients (especially nitrogen) left from the previous crop.

• Increase biological activity of the soil,

• Reduce soil erosion

• Absorb and store rainfall.

• Not much tolerance to heat or drought (more than rye).

• not as good at breaking up compacted subsoil

• Beware GMO canola from feed store “horse oats.” Buy organic!

Less allelopathic effect than winter rye. Maybe good or bad. . .

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. Other crops which winter-kill at 5-20°F (-15°to -7°C) include barley, berseem clover, Lana vetch, purple vetch, fava beans, Canadian/spring field peas, oil and fodder radish.

2. Frost-tender sorghum-sudangrass hybrid, buckwheat, soy, southern peas, Miami peas, sunn hemp and millets.

They can be used before early spring food crops.

Sorghum sudangrass hybrid. Photo by Bridget Aleshire

Part 2. Under-sowing 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.)

• Choose vigorous food crops, but cover crops that are only moderately vigorous.

• 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. Often the best time is at the last cultivation.

• The leaf canopy of the food crop should not yet be closed. With vining food crops, sow the cover crop before the vines run.

• Ensure a good seedbed and a high seeding rate. • Irrigate sufficiently. 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.

Example of undersowing oats and soy • We undersow our 6th sweet corn (sown 7/16) 4 weeks

after seeding, with oats and soy in mid-August.

• 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.

• Oats and soy are both winter-killed in our climate, so they make good companions.

• They are both somewhat shade-tolerant.

• They also tolerate foot-traffic when it’s time to harvest.

• After harvest, we do not mow down the corn, but just leave it until early spring. It incorporates pretty easily by then.

• In mid-March we follow with our spring potatoes.

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 cover 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, and broadcast a mix of clovers (late August-early September)

• 1 oz (30 g) Crimson clover, 1 oz (30 g) Ladino white clover and 2 oz (60 g) medium red clover per 100 sq ft (9 m2)

Clover green fallow in July. Photo by Bridget Aleshire

Clover fallow details • Crimson clover is the fastest growing in the

fall, and the others take over the next year.

• White clover: 3 main types – use the large (12”-15”, 30-32 cm) Ladino, that produces the most biomass and the most N. The dwarf type (Wild White) is used for high traffic areas like orchard alleys; the intermediate-height range (up to 12”/30 cm) 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.

Broccoli with clover under-sown. Photo Nina Gentle

Green fallow decision points We hope to keep the clover growing for the whole next year. Back-up plans:

• In March, we bush hog the old brassica stumps and let the clovers flourish.

• If the plot is not too weedy, we keep the clovers, 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, pearl millet, sorghum-sudangrass) until August, then oats.

• In July, if the weeds in the clover are bad we disk and sow sorghum-sudangrass mixed with soy, to winterkill. 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. Pearl millet is better.

• In August, if the weeds are gaining the upper hand over the clovers, 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.

Part 3. Hardy grasses – 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

Hardy grasses – winter rye Winter Rye (cereal rye)grows 5’-7' (1.5 – 2 m) 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

Part 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

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.

Suitable cover crops for no-till Do you want a winter-killed cover crop or a hardy one?

Consider when you can plant the cover crop and when you need to plant the food crop.

Consider efficacy in producing biomass and fixing nitrogen.

Using a mixture of grasses and legumes helps limit the loss of N from the cover crop through leaching or denitrification. But legumes are wasted money if you can’t grow them close to flowering stage.

There are advantages to including more than one legume in the mix – in unusual weather, one may struggle, while another does better.

Austrian winter peas with winter rye. Photo Cindy Conner

• Use Frost-tender cover crops 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 for early spring vegetables

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%.

Hairy vetch activates plant genes that increase disease- tolerance and plant longevity, giving tomatoes an extra 2 to 3 weeks of production

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. Kill the clover by mowing after early bud

• At the Coastal Plain Experiment Station in Tifton, GA, they are trying peanuts planted into crimson clover.

• If you have machinery or hand tools for seeding into no-till cover crops, direct seeded crops are possible.

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. 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 (45 g) HV, 1.5 oz (45 g) AWP, 2.5 oz (75 g) Rye per 100 sq ft (9 sq m)

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”(10 cm) tall before hard frosts of 22°F (-5°C) 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. The vetch and peas (if plentiful) supply all the nitrogen the tomatoes need.

7. 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.

Flowering hairy vetch with rye at mowing stage. Photo by Bridget Aleshire

No-till cover crops continued

8. The dead mulch keeps weeds away for 6 -10 weeks in our humid climate, then biodegrades.

9. In July we roll hay between the rows, to top up the mulch. We plant the tomato rows 5.5’ (1.6 m) 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 Initial hopes for no-till cover crops - that it would be

possible to grow vegetables organically without ever tilling

again - were unrealistically high.

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.

Part 5. Including winter-hardy legumes

Crimson clover flower, Photo Kathryn Simmons

For maximum N, mow and incorporate legume 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.

Austrian winter peas can be sown later than clovers.

Hairy vetch Very widely-adapted, cold-hardy to

−15°F (-26°C)

Needs a minimum soil temperature of 60°F (16°C) to germinate

Sow 40-60 days before the first 28°F (-2°C) frost

Grows quickly in the fall

During the spring it reaches a height of 2' (60 cm) alone or 6' (1.8m) if mixed with tall cover crops.

In zone 7, 9/7–10/10 is ideal for sowing. Don’t delay - over 1100 GDD are needed in 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 Main uses : 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.

Clovers attract beneficial insects and reduce aphids.

“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

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

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

Blooms 2 weeks before hairy vetch

Winter-kills in zone 6, hardy in zone 7. OK

to 0°F (-18°C).

Can sow several weeks later than clovers

Sow at least 35 days before first hard

freeze (25°F/-4°C) - in zone 7, 8/10–10/24

(11/8 OK)

Optimum temperature for germination is

75°F (24°C), min germination temperature

41°F (5°C).

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

Austrian winter peas in our rotation L

ate

-fin

ishin

g

cro

ps

winter squash, melons, sweet potatoes, tomatoes, peppers, middle sweet corn, June-planted potatoes

Sow

Sow

Austrian Winter Peas

Oct 1-Nov 7

With winter wheat or rye

Cro

ps aft

er

Ma

y1st

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 last year’s seed.

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 a sowing date to get plants 6-8” (7-20 cm) 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.

Early spring cover crops we use at Twin Oaks

In February or March we sow oats, where we will not be planting a food crop for 8 weeks and we have winter weeds, and no cover crop. Enough time for oats 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, when it’s 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)

Section D

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. Photo Kathryn Simmons

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.

Sweet corn with undersown soy cover crop. Photo Kathryn Simmons

Warm weather legumes - southern peas

• Most southern pea varieties mature in 60-90 days and will be killed by the first frost. (Oats may provide temporary protection).

• Iron and Clay southern peas are often used to break up compacted soil

Iron and Clay Cowpea. Photo Southern Exposure Seed Exchange

• Buckwheat can be under-sown in spring or summer vegetable crops, to take over after the food crop is finished. Millets and southern peas or white clover also.

• Winter squash, watermelon or sweet potatoes can be undersown, 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 up.

• 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.

Under-sow summer cover crops too!

Buckwheat A warm-season broadleaf annual germinating in just a few days Takes only 30-50 days to grow to full height of 2-3' (60-90 cm) Quick to incorporate, easy with hand tools or small equipment. Sow from around the last frost date to late summer (50 days before first frost). Incorporate 7-10 days after it starts flowering, or it can be left to self-seed if there is time for several sequential plantings of buckwheat. If the soil is too wet to disk or till, it can be mow-killed or rolled. A useful cover crop in case of crop failure or early end of a food crop. Use to prepare land for perennials or to bring neglected land back into production.

Buckwheat flower.

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 extracts K, Ca and P from 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).

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 Not great at reducing soil compaction, preventing erosion, or scavenging nitrogen.

o The summer weeds most likely to grow in gaps in buckwheat are redroot pigweed, lambs-quarters and barnyard grass.

o Provides relatively little biomass – decomposes fairly quickly if cut and left on the surface.

o May harbor root lesion nematodes (not root knot nematodes).

Brassica cover crops for pest control • We tried a forage brassica

(canola/rape), before a new strawberry planting, but we got 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 (-2°C) frost.

• Brassicas produce allelopathic compounds that inhibit weeds and biotoxins (glucosinolates) that kill pests. Photo Kathryn Simmons

Section E

Root knot nematodes • Peanut Root Knot Nematodes popped

up part of our hoophouse in 2010.

• We have grown nematode-suppressing cover crops, wheat and white lupins, OP French marigolds, sesame, from September to June.

• We solarize 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: Juncea mustards, kale, Yukina Savoy, Chinese cabbage, pak choy and radishes in winter, West Indian gherkins, Mississippi Silver or Carolina Crowder southern peas in summer.

Photo Credit University of Maryland Plant Diagnostic Laboratory

64°F (18°C) is the threshold soil temperature for nematode reproduction

Cover crop mixes • A mix of several cover crops will provide more resilience in the face

of extreme weathers. One may struggle, while another does better. Mixes can give the advantages of each of the components.

• First select 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” (7.5 cm) 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 1/3 (not 1/2)

• Generally, use a grass/legume mix in a 2:1 ratio, although you can use higher amounts of legumes, up to 1:1.

• 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%.

Section F

Resources - General ATTRA attra.ncat.org Many helpful publications

SARE sare.org -A searchable database of research findings

SARE Managing Cover Crops Profitably. 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.

VABF vabf.org/seeders-using-manually-operated-seeders-for-precision-cover-crop-plantings/ Seeders: Using Manually-operated Seeders for Precision Cover Crop Plantings by Mark Schonbeck/RonMorse

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 - 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 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 cog-shop.myshopify.com/)

Northeast Cover Crops Handbook Marianne Sarrantino

Jeff Moyer Organic No-till Farming rodaleinstitute.org/shop/organic-no-till-farming/

Resources - slideshows My presentations are available at Slideshare.net. Search for Pam

Dawling: There is a longer version of Cover Crops for Vegetable Growers.

Planning the Planting of Cover Crops and Cash Crops, Daniel Parson slideshare.net/parsonproduce/southern-sawg

Cover crops for vegetable cropping systems, Joel Gruver

slideshare.net/jbgruver/cover-crops-for-vegetable-crops

Several other slideshows on cover crops Joel B Gruver www.Slideshare.net

Cultural Practices And Cultivar Selections for Commercial Vegetable Growers Brad Bergefurd .slideshare.net/guest6e1a8d60/vegetable-cultural-practices-and-variety-selection

Conservation Systems Research, USDA-ARS Auburn University, Cover Crops for the Southeast ars.usda.gov/ARSUserFiles/60100500/SlideSets/SS01.pdf

Rodale Institute Impacts of plastic and cover crop mulches slideshare.net/greenjeans76/weaver-fieldday-ziegler20120810?from_search=1

Resources – Cover Crops 1 CEFS Organic Production: Cover Crops for Organic Farms, cefs.ncsu.edu/wp-

content/uploads/covercropsfinaljan2009.pdf?3106e7

eOrganic Agriculture Resource Area of the eXtension website, Cover Cropping in Organic Systems eorganic.org/menu/872. (many useful documents.)

Penn State Extension, Making the Most of Mixtures: Considerations for Winter Cover Crops in Temperate Climates http://mccc.msu.edu/wp-content/uploads/2017/02/PA_2015_Making-the-Most-of-Mixtures.pdf

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. portal.nifa.usda.gov/web/crisprojectpages/0225690-finding-the-right-mix-multifunctional-cover-crop-cocktails-for-organic-systems.html

Sequester soil organic carbon aces.illinois.edu/news/cover-crops-can-sequester-soil-organic-carbon

Mark Schonbeck carolinafarmstewards.org/wp-content/uploads/2012/12/1-Schonbeck-Principles-of-Sustainable-Weed-Management-in-Organic-Cropping-Systems.pdf

See Rodale plans by Greg Bowman for a roll-kill roller at croproller.com/ or build your own newfarm.org/depts/notill/features/2006/0506/drawings.shtml

eorganic.org/node/2594#.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 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. 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. 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 countrylivinggrainmills.com/grainmill3.html

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 from Clayton Carter github.com/claytonrcarter/cropplanning

Mother Earth News interactive Vegetable Garden Planner, free for 7 days: motherearthnews.com/garden-planner. Also on SESE (works on smartphones): gardenplanner.southernexposure.com/

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/

Johnnys Seeds Planning Tools and Calculators johnnyseeds.com/growers-library/online-tools-calculators.html

Jean-Paul Courtens, Roxbury Agriculture Institute. Harvest Manual, Crop manual, Soil Fertility Info. roxburyfarm.com/roxbury-agriculture-institute-at-philia-farm.

Mark Cain www.drippingspringsgarden.com Download the CSA 2019 harvest schedule. (38kb PDF) Notebook-based system.

Growing Small Farms growingsmallfarms.ces.ncsu.edu/ Farmer Resources /Farm Planning and Recordkeeping.

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 2019

Author of Sustainable Market Farming and

The Year-Round Hoophouse

www.sustainablemarketfarming.com www.facebook.com/SustainableMarketFarming