green fallow – Sustainable Market Farming

Cover crops for August: Oats and Barley

Note: I edited this post in September when I found I was mistaken in believing barley was less cold-hardy than oats.

Focus Cover Crops for August: Oats, barley and other winter-killed cover crops

In August we are looking ahead, thinking about how our cover crops will be impacted by future cold weather. In July I wrote about hot weather grass cover crops, including Sorghum-Sudan hybrid (Sudex), and the millets, which are not frost-hardy.

German/Foxtail and Japanese millets are day-length sensitive. Growth is considerably less if they are sown after the summer solstice, so they are likely to be of limited use as cover crops once we reach August.

Browntop Millet could be useful in August in the mid-Atlantic. Proso/Broomcorn Millet I’m not so sure about. Pearl/ Cattail Millet is not day-length sensitive. To winter-kill and avoid seed formation, sow 60-85 days before your expected first frost.

See Working with the time you have left in the post Cover Crops in Summer. See No-Till summer cover crops in that same post (Soy, southern peas, foxtail millet). Also there, see Five Easy Summer Cover Crops that Die with the Frost (buckwheat, sorghum-sudan grass, soybeans, southern peas and sunn hemp.)

Buckwheat cover crop in flower.
Photo Pam Dawling

Buckwheat can be sown up to 28 days before the first frost. See my article about buckwheat. Soybeans can be sown up to 45 days before frost. A mix of sunn hemp, soybeans or southern peas and other frost-tender cover crops can be grown during August (60-80 days before frost) before planting garlic in mid-fall. This method will work more easily if you mow the cover crop around your frost date, so that it is easier to make furrows in the soil. Forage radish, lab-lab beans or bell beans sown now will die back and leave almost bare soil. This is a boon for the very earliest spring transplants or sowings.

Or, instead of sowing a cover crop now, you could sow a fast-growing vegetable crop. Kale, spinach, Tokyo bekana, radishes, chard, lots of salad crops, senposai, mizuna, tatsoi, or land cress. Try Eat-All Greens, an idea form Carol Deppe. Patches of carefully chosen cooking greens are sown in a small patch. When it reaches 12″ (30 cm) tall, Carol cuts the top 9″ (23 cm) off for cooking, leaving the tough-stemmed lower part, perhaps for a second cut, or to return to the soil.

Twin Oaks Eat-All Greens on October 19.
Photo Bridget Aleshire

Winter-killed, not frost-killed, cover crops

In August, we can sow winter cover crops to be winter-killed for easy soil cultivation before early spring vegetables. Oats and barley are in this category. Oats will be killed by three nights of 20°F (-7°C) or a single night of 6°F (-14°C). Sow oats 5-8 weeks before your average first frost to get good size plants before they get winter-killed. We sow in late August and early September in Zone 7a. See Cover Cropping Your Garden by Chris Blanchard in 2002:

“Inexpensive and easy to grow, oats are a standard early fall cover crop in the northern and middle sections of North America. A quick-growing, non-spreading grass, oats will reliably die in Hardiness Zone 6 and colder, and often in zone 7.”

It used to be nine years out of ten, here in Louisa County, VA, but our climate is shifting to be too warm in winter to reliably kill oats. This past winter (2022/2023) oats did not die. They were cold-damaged, and set back, but definitely not dead.

We can no longer rely on our winter cover crop oats getting winter-killed. March photo by Pam Dawling

Fall-sown Barley (Hordeum vulgare), grows even faster than oats, although not as fast as winter rye, and it won’t die as early in the winter as oats. Barley dies at 17°F (-8°C). It usually will die in Zone 7 and colder regions. The dead barley residue protects the soil through the winter, and dries into what Barbara Pleasant calls “a plant-through mulch” in spring in cold zones.

See Planning Winter Cover Crops. If the area has been fully harvested of food crops by 60-80 days before frost, sow a frost-killed cover crop or even a fast-growing food crop. In central Virginia, it’s a mistake to sow rye as early as August, as it can set seed.

Winter-hardy cover crops to sow in August

Not all winter cover crops can be sown as early as August in the mid-Atlantic. Don’t sow winter rye, or it may head up before winter and drop seeds. Only sow oats or barley if you are sure you can get them turned under or killed by cold winter weather before they seed. They will not mow-kill. Be careful buying feed-grade seeds (rather than seed-grade), as they can contain weed seeds including GMO canola.

Clovers can be sown in August (provided you can supply enough overhead irrigation). September is a better time to sow clovers here, if you are sowing them in bare ground. They will make some growth in our climate before winter, and then a lot more once spring arrives.

Secondary Cover Crops in August: Undersowing for more cover crops

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.

Green fallow (Full year cover crops)

Fall broccoli undersown with a mixed clover winter cover crop.
Photo Nina Gentle.

Our main use of clovers is to undersow fall brassicas such as broccoli and cabbage, with a mix of Crimson clover, white clover and medium red clover in August, to form a green fallow crop (all-year cover crop) for the following year, replenishing the soil and reducing 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)
In March, we bush hog the old brassica stumps and let the clovers flourish, mowing once a month to prevent the crimson clover and the annual weeds from seeding.

See my Mother Earth News post: Late summer and fall intercropping of cover crops in vegetable crops, aka undersowing.

If you have difficulty getting even coverage when broadcasting clovers or other cover crop seeds, try seeding half the crop walking in one direction, and then seed perpendicularly across your original path

In mid-August, we undersow our last sweet corn planting with oats and soybeans, as the winter cover crop, which winter-kills, leaving a plot that is easily worked up next spring. Our 6th sweet corn is sown 7/16. 4 weeks after seeding, we cultivate and sow oats and soy. In mid-March we follow with our spring potatoes. Both oats and soybeans have some tolerance for shade and for foot traffic (harvesting corn!).

Late season sweet corn undersown with oats and soy
Photo Kathryn Simmons

Sweet corn can be undersown with clover rather than soy or oats in some climates. We tried clover but found it harder to germinate in hot weather, and harder to keep the tiny seed damp. Buckwheat can be undersown in corn as a short term summer cover, but according to Sue Ellen Johnson, (co-editor of Crop Rotation On Organic Farms: a planning manual, it grows rather straggly in the shade of the corn. Soy has the advantages of tolerating shade as well as foot traffic.

We tried an idea from NY State, or undersowing winter squash with buckwheat and tilling it under just before the vines run (that was June), but here in the south, the vines ran too fast. We ended up having to wade in among the vines to pull up the buckwheat by hand!

You can drill cover crop seeds using a push seeder. See VABF Using Manually-Operated Seeders for Precision Cover Crop Plantings on the Small Farm. Don’t worry if the seed ends up deeper than ideal. It will still germinate. On a small scale, you can sow by hand, either broadcasting and raking in, or in close rows using a hoe, as if sowing

Cover Crop Planning

My book Sustainable Market Farming has a chapter on cover crops and 9 pages of charts about particular options.

The book Managing Cover Crops Profitably (third edition) from the Sustainable Agriculture Research & Education Program (SARE), is the best book I know on the subject. You buy the book for $19 or download it as a free PDF from SARE.

Good news – great hoeing weather! Bad news – more nematodes in the hoophouse

Fall broccoli last year. Credit Ezra Freeman — Fall broccoli last year.
Credit Ezra Freeman

Last week I wrote about transplanting cabbage and sowing kale. We were having “great transplanting weather”, that is, it rained a lot! We filled all the gaps in all 12 rows of broccoli and cabbage in a single hour with four people. There weren’t many gaps, happily. That’s about 1400 broccoli plants and 700 cabbages, our usual amount to feed a hundred people.

This week in the garden, it’s about three weeks since we started the transplanting, so the first rows are ready to be uncovered and hoed. Happily, we now have great hoeing weather! No rain in sight for a week. Central Virginia weather is very variable, and our particular spot is drier than the surrounding area, so if the forecast says 30% chance of rain or less, we are very unlikely to get any. There’s currently a forecast with a 50% chance of rain in 6 days (Monday night). If we can get all the hoeing done, and till or wheelhoe between the rows, then I can broadcast a clover mix and welcome some rain! We like the wheel hoe if the weeds are not too big and not too grassy. The first few rows were quite grassy, so we used our BCS 732 tiller from Earth Tools.

We cultivate around the brassica plants, then broadcast a mix of clovers: 1 oz crimson clover, 1 oz large white Ladino clover and 2 oz common red clover (medium, multi-cut) per 100 square feet. Then if it doesn’t rain, we water like crazy for a few days, which is all it takes to get the clover germinated. We have drip tape for the brassicas, but we need overhead sprinklers for the clover mix. The crimson clover is the fastest growing in the fall, and the others gradually take over in the spring and summer of the next year. We like watching the progression from crimson clover to red to white as each type comes into its strength.

This method of undersowing clovers in fall brassicas works well for us. It provides cover for the soil, legumes which provide nitrogen for the crop. The clovers survive the winter, and in the spring, we mow off the dead broccoli stems and let the clover grow. If all goes well, we keep the clover mix for a whole year (our Green Fallow Year), feeding the soil and eliminating weed seeds. We mow it to prevent the crimson clover seeding (which could be a nuisance) and when ever any weeds seem to be gaining. Here’s a couple of pictures from a previous year. (That’s our Dairy Barn by the side of the driveway, and our Hay Barn in the distance.)

Broccoli in fall after the clovers grow. Twin Oaks Community — Broccoli in the late fall after the clovers grow.
Twin Oaks Community

In March, the old broccoli trunks are surrounded by a sea of green clover. Photo by Kathryn Simmons — In March, the old broccoli trunks are surrounded by a sea of green clover.
Photo by Kathryn Simmons

I’ve written up this method as part of an article for Growing for Market magazine, for the September issue.

And now our bad news – more nematodes in the hoophouse. When we pulled up our early tomatoes, the roots of four of them in one bed were gnarly with lumps. It’s the return of the Root Knot Nematodes.

In the early spring of 2011 we found spinach with lumpy roots. We sent some plants with soil attached, to the Plant Diseases Clinic and got the diagnosis of Peanut Root-Knot Nematodes. We put that half a bed into a series of cover crops, (wheat and white lupins in the winter, French marigolds and sesame in the spring) and solarized it each summer, for two years. In the summer of 2013, we grew Mississippi Silver cowpeas there (resistant to RKN). This past winter we grew lettuce in the that affected half-bed. We benefited – no sclerotinia drop in that lettuce crop, thanks to the summer solarization!

Meanwhile in the early summer of 2013, we found some beans with lumpy roots in the other half of the bed, so we started the same treatment there. Next summer (2015) we could grow the cowpeas there.

Our first (baggy) attempt at solarization in the hoophouse. Credit Kathryn Simmons — Our first (baggy) attempt at solarization in the hoophouse.
Credit Kathryn Simmons

But now the next bed over has nematodes. Having a half-bed out of production is manageable, but one and a half is more of a blow. We are considering whether we need to be as cautious, or whether we should accept that some level of nematode infestation is likely in hoophouses in the south. We are looking at various scenarios. This research has consumed all my available time this week. Information about nematodes is sometimes too general to be useful, as there are many kinds other than root-knot ones. Plus, what’s true for Peanut RKN is not necessarily true for Southern RKN or Northern RKN. Grr!

I’ve assembled a long list of tomato varieties resistant to some kind of RKN, although I don’t yet know which of them are resistant to Peanut Root-Knot Nematode. Many, many food crops are susceptible. Most of the resistant crops are ones we don’t want to grow in the hoophouse: Jerusalem artichokes, globe artichokes, asparagus, horseradish, rhubarb, maybe sweet corn (opinions vary on its resistance/susceptibility).

Maybe we could grow West Indian gherkins one summer. We’d get soooo many pickles! It’s a very productive crop for us. One idea was to build a second hoophouse and use the old one for (resistant) strawberries for two years! We’re not really at the place to do that, though, financially or time-wise.

Currently I’m studying a list of biocontrols to see what’s available and affordable. Life goes on. Hopefully we can decide at our crew meeting on Thursday, because we can’t start to implement our fall planting schedule in the hoophouse until we decide about the nematodes.

Twin Oaks Garden Task List for April

Asparagus in early April.Credit Wren Vi — Asparagus in early April.
Credit Wren Vile

All Month:

Lettuce Factory: In flats, (on greenhouse bench) sow lettuce #7, 8, 9 (romaines & small varieties to interplant with peanuts). Transplant 1/3 bed lettuce (120 plants)/week. Plant #4, 5, 6 this month.
Compost Needed for April: 6-9 tractor buckets for beds, 24-30 bkts to disk in.

Early April:

In greenhouse, sow lettuce #7;

Keep celery above 55°F, and celeriac above 45°F (don’t put in coldframe). 10 consecutive days <55°F for celery, <45°F for celeriac, causes bolting.

Spot lettuce, harden off in coldframe. Spot peppers, tomatoes, & eggplant. Protect new pepper seedlings from mice. Keep tomatoes above 45°F at night, eggplant above 55°F.

Cut sweet potato slips at 6-12”, put in water. Once a week, plant rooted slips in 4” flats.

Sow outdoors: carrots #5, beets (see March notes), parsnips with radishes #2, (in celery bed), sunflowers.

Weed and thin early crops. Side dress or foliar spray over-wintered spinach to boost production.

Take rowcover from turnips, senposai, cabbage #1, kohlrabi, little alliums, onions as needed for broccoli.

Transplant lettuce #4, main cabbage & broccoli under rowcover (12 pieces) within 6 weeks of sowing.

Till beds for mid-April. Compost beds for late April plantings.

Garlic bulbing is initiated on/after April 10 (13 hours daylight), and soil temperature above 60°F.

Mid April:

In greenhouse sow melons #1 in soil blocks or plug flats, replacement paste tomatoes, lettuce #8, and okra.

Sow beans #1 when lilac in full bloom, sunflowers. Sow edamame #1, corn#1, if warm, and soil >60F.

Till beds for late April (chard, cowpeas, peanuts). Compost beds for early May (okra, toms, melons, celeriac, lettuce 7,8,9, asparagus beans)

Hill up potatoes when 6” high. Cover half the vine. Repeat after 2 weeks. (Flameweed if too wet to hill.)

Take rowcover from kale, collards, early lettuce for raised bed tender crops.

Transplant broccoli #2, insectary flowers #1, bulb fennel, lettuce #5, cukes #1 w/nasturtiums, zukes #1; use spring hoops for cucurbits. Take rowcover from spinach to strawberries.

A fine bed of fava beans. Credit Kathryn Simmons — A fine bed of fava beans.
Credit Kathryn Simmons

Install stakes every 8-10’ for peas and fava beans, and stringweave them to final height of that variety.

Weed garlic [or flameweed it early in the morning after a good rain. Direct flame at base of garlic plants]

Harvest lettuce as heads rather than leaves, from 15 April

#3 Spring Tractor Work (mid April) – Disk areas for sweet potatoes, winter squash, watermelons, (Romas and peppers if no-till cover crop insufficient). Bush-hog late food crop plots when rye heads up, to help clover or peas develop. Also clover patches, eg Green Fallow (All Year Cover Crops).

Late April:

in greenhouse sow lettuce #9; watermelons #1 & 2 in soil blocks or plug flats; calendula and various insectary flowers, filler corn & Romas.

Sow corn #1 (1/2-3/4” deep) in two phases, and peanuts if soil temperature is 65°F. Also cowpeas #1, and sesame.

Sow more leeks if needed in Little Alliums bed outdoors. If not, sow more mini-onions and scallions #3.

Transplant lettuce #6, leaf beet, chard, insectaries; finish transplanting gaps in the main broccoli & cabbage plot, plant Alyssum. Take rowcovers from broccoli & cabbage for new crops.

If mild, plant tomatoes. Harden off nightshades by restricting water.

Till beds for early May (okra, toms, melons, celeriac, lettuce 7/8/9, asparagus beans). Compost beds for mid-May (edamame, eggplant, limas).

Store spring and fall seeds (spinach, peas, beets) in the basement for the summer.

Foliar feed the potatoes, ideally the morning before hilling up, and every 2 weeks.

Roll out Driptape and Biotelos corn plastic mulch for peppers and Romas where no-till cover crop not used.

Cover crops: sow rye to wimp out. Sow buckwheat in any beds not needed for at least 5 weeks eg. leeks limas; add soy if bed not needed for 7 weeks.

Haybine or bush-hog vetch & rye for no-till planting of Roma paste tomatoes, late in the month (or very early in May). (Mow strips; or till strips through the cover crop for the rows, with narrow-set tiller). Water the area before digging holes, if dry.

Perennials: Weed blueberries, asparagus, raspberries, strawberries, grapes as needed. Mow aisles. If asparagus weeds are getting out of hand, mow down one or more rows to keep control. Monitor asparagus beetles, spray spinosad when bees not flying, if >10 adults/100 crowns. Spinosad: Shake well, 1-4 Tbsp/gall (1fl.oz=2Tbsp=30ml.) Repeat in 6 days.

The black center of this strawberry flower show that it was hit by frost and no berry will develop.Credit Kathryn Simmons — The black center of this strawberry flower show that it was hit by frost and no berry will develop.
Credit Kathryn Simmons

Cover strawberries if frost threatens – take rowcovers from spinach. (Pick flowers off any new spring plantings.)

Visit grapes, log progress, remove flower buds from new vines. Note deaths and where replacement arms are needed. Check and repair fruit drip irrigation, thin raspberries to 6/foot of row.

Harvest and weed: Asparagus, chard (hoophouse), collards, garlic scallions- pull at 8″, kale, leeks, lettuce, radishes, rhubarb, senposai, snap peas in hoophouse, spinach.