Cover Crops for February: Oats if you have a 6–10 week gap

Oats Cover Crop, Steve Groff farm, Holtwood PA. SARE Soil Health Resources

Cover Crops for February: Oats if you have a 610 week gap

In February, you’ll hopefully have made your crop plans and maps. Perhaps you’ve discovered some beds with no winter cover crop, that you are not using for early spring crops? Those winter annual weeds, chickweed, dead nettle and henbit, will shed lots of seeds if you let them.

If food crops were harvested too late to sow any winter cover crops, in early spring you will be looking at weeds, or “spontaneous vegetation” as I’ve heard them euphemistically called. The first year I gardened in Virginia I had lots of beds in April with purple flowers (henbit, purple dead nettle, some ground ivy) and I couldn’t think what to do – I didn’t need those beds for a few more weeks, so I wasn’t ready to till them. Oh, so wrong! I had squandered an opportunity to improve the soil as well as deal with weed seeds.

Now, when we have the crop plans made, we tag any beds that won’t be used for six weeks or more, till in the weeds and sow oats. In February or March here, with a last frost date of April 30, six weeks is just enough time here to make enough growth to out-compete the weeds and add to the organic matter in the soil.

Examples of crops in our gardens that occupy beds too late for us to sow winter cover crops include late cabbages, the last lettuce, leeks and fall Asian greens. Examples of late spring crops the next year include eggplants, peppers, tomatoes, edamame and chard. In some cases, we might even have no food crop planned until August or the beginning of September.

Six–ten weeks (depending on your climate) is long enough in early spring to get worthwhile growth from oats before prepping for the food crop.

Once we get to March 31 here, it is too late in the year for oats (they will quickly head up after making very little growth) and too soon to rely on frost-tender cover crops. See the section below on Stale Seedbed Technique.

Oats Cover Crops Steve Groff farm, Holtwood PA SARE Soil Health Resources

I wrote about oats as a winter-killed cover crop in August.

Will oats work as an early spring cover crop for you?

Large oat plants will be killed by three nights at 20°F ((–7°C) or by a single plummet to 6°F ((–14°C). Oats seedlings die at 17°F (–8°C). Consider your likely nighttime low temperatures during the period in question, and how likely your seedlings are to die. Oat cover crops of a medium size die around 10°F (–12°C). If they die after growing to adolescent size, no worries – just till them in before planting your next crop.

The minimum soil temperature for germination of oats is 38°F (3°C), and the time required to grow to a worthwhile height in cool weather is 6–10 weeks.

If you are in zone 8 or warmer, oats will not winter-kill, and can be grown in winter too – they may not reliably mow-kill, but are relatively easy to incorporate.

Oat plant and seeds. SARE

Pros and cons of oats as a cover crop

Like most cover crops, oats add biomass and nutrients, increase the biological activity of the soil, smother weeds, reduce soil erosion (their fibrous roots anchor the soil) and absorb and store rainfall. Oats are easy to establish, are fast-growing and particularly good at shading out germinating weed seeds and at salvaging any nutrients (especially nitrogen) left from the previous crop and making them available to the following crop.

In early spring you won’t get as much biomass as from a fall oat cover crop, when you can get. as much as 2000–4000lbs per acre (2240–4480 kg/ha. Certainly not enough to be a no-till cover crop for your next food crop. Oats provide some allelopathic effect (producing biochemicals which inhibit the growth of other plants) although less than winter rye. Like most plants, oats form arbuscular mycorrhizal associations (fungi penetrate the plant’s cell walls and help capture nutrients from the soil) – a mutually beneficial relationship, although probably not a big feature when conditions are cold.

Oats are not as good as some other cover crops at breaking up compacted subsoil, although they do loosen the upper layers of topsoil nicely. (Just where you are going to sow.) Oats do not add nitrogen, and unlike flowering cover crops, they do not attract beneficial insects (assuming they are turned under or mowed before heading up and shedding pollen).

Common Oats. Buy Organic and avoid GMO canola seed inclusions

Buying oats, sowing rates

We used to buy “horse oats” (feed oats) locally and not worry about organically certified seed. But I noticed canola sprouting along with the oats, and I don’t want GMO canola going feral in our gardens! We plan ahead and order extra Organic spring oats in summer when making our big cover crop seed order.

Oats will grow in soils with a pH range of 4.5–7.5, and even do OK in soils without great fertility. They have some tolerance to flooding, but not much to heat or drought (although more than rye).

The sowing rate for drilled oats alone is 80–100lbs/ac (90–123 kg/ha). The broadcast rate is 110–140lbs/ac (123–155kg/ha). On a small scale, this is 4–6 oz/100 sq ft (12–20gm/sq m). Aim to cover the seed to a depth of about 1″ (2.5 cm).

Oats grow to a height of 2–4 feet (0.6–1.2 m) if not killed before then.

Stale seedbed technique and tarping

If you have less than 8 weeks until you need to plant the food crop, you are better off mowing when you can, or weed whipping, to prevent weeds seeding.

Tarping beds to kill weeds.
Photo Cornell Small Farms Unit

You could mow and tarp. I don’t yet have much experience of tarping, but there are good directions in The Lean Micro-Farm and The Market Gardener. There are also online videos. The basic idea is to mow the bed, cover it with a black plastic silage tarp, weight down the edges to get good soil contact and stop the tarp blowing away, and wait till the plant matter has disintegrated, or until you need to use the bed. This will take several weeks in cold weather, (although only a few weeks in summer). If you have a late-finishing fall crop, you could mow and tarp as soon as the crop is finished, and leave the bed tarped until spring. Weeds germinate under the tarp, but then die without light.

For a stale seedbed technique without tarps, you could mow, till several weeks before planting, water (if it doesn’t rain) to germinate weeds, and hoe off those weeds once a week. This can really help reduce the weed seedbank in the soil. It is particularly useful before sowing small seeds of slow-growing crops, such as carrots.

What not to sow in short gaps in early spring

Other quick cover crops, like buckwheat and soybeans, are not at all frost-hardy, so wait until after your last frost date to sow those.

In early spring, the air and the soil are cold, and sowing a fast-growing vegetable crop will not be successful with a gap of less than eight weeks. Crops take too long to grow at this time of year.

 Spring gaps longer than eight weeks

If you have more than eight weeks you could try those fast-growing vegetables: kale, spinach, Tokyo bekana, radishes, chard, lots of salad crops, senposai, mizuna, tatsoi, land cress. Or try Eat-All Greens, an idea from 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.

Young spinach seedlings.
Photo Pam Dawling

Undersowing oats in spring

Another way we have used oats in spring is between rows of peas (grown on the flat, not in beds). We sowed the oats the same day as the peas, and lightly tilled the oats in. We mowed the oats as needed during the pea training and harvest period to make access easy. This reduced the number of weeds, and we quite liked the “lawn” underfoot!

Green fallow (Full year cover crops)

If you have a bed with no crop planned for the whole season, you could grow a Green Fallow. You can plant long-term cover crops to replenish the soil. Start with oats or one of the more cold-hardy grasses, and once we get to warm weather, after the frosts, till that in (or mow if it mow-kills) and sow warm weather cover crops.

Reasons not to do no-till food crops in spring

Untilled soil in spring is colder than tilled soil, and growth of anything you plant in it will be slower, and harvests delayed. You could consider broccoli or cabbage, perhaps, but not warmth-loving crops. You may get more slugs and/or more fungal diseases with no-till. The cover crop could try to regrow, or you could get some weeds anyway.

Also, if you are planting by hand, transplanting into untilled soil is harder work than planting into loose tilled soil. Hand-sowing into untilled soil is tricky – winter snow and ice can leave quite compacted soil. If the notion of organic no-till appeals to you, experiment on a small-scale the first year. Reduced tillage is another option. Till out narrow strips in the oats for your plantings of large food crops normally grown on a wide row-spacing.

Using a push seeder for cover crops

EarthWay push seeder.
Photo from EarthWay

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.

 

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 or download it as a free PDF from SARE.

Twin Oaks Garden Task List for February

Greenhouse interior with early spring seedling flats.Photo Kathryn Simmons
Greenhouse interior with spring seedling flats.
Photo Kathryn Simmons

PlanningWeek 1:  Revise Crop Planting Quantities chart, Perennials worksheet, Harvest and Food Processing Calendars, Veg Finder, and Phenology Chart. Week 2:  Revise Fall Brassicas Spreadsheet, Onion Plan and Log, Sweet Potato Plan. Revise and post Paracrew Invitation. Week 3: Write Seed Saving Letter. Revise Blueberry Map and Log, Grape Map and Log. Week 4: Revise Crop Planting Specs sheet, revise Garden Planning Calendar, File notes, prune files.

Lettuce Factory: Sow lettuce #3, 4 in flats (short-day fast varieties, every 14 days).

Spread compost & till beds for spinach, beets, favas, lettuce, onions, little alliums, turnips, senposai, kohlrabi, cabbage, kale, collards when soil dry enough.  Till beds for carrots 1-3, with or without compost.

#1 Spring Tractor Work  – Compost and disk areas for broccoli and potatoes when dry enough, or till.

Early Feb: in greenhouse sow: cabbage, collards, senposai, kale, kohlrabi, broccoli #1, celery, celeriac

Sow spinach outdoors if Jan sowings fail: 4oz/bed pre-sprouted. Transplant spinach from hoophouse [or flats].

Sow fava beans (seed is in peas bucket). Plant small potato onions if not done in January.

Mid-month: in greenhouse: Sow lettuce #3, and resow hoophouse peppers as needed. Spot cabbage, lettuce#3, hoophouse peppers, kale, collards, and harden off.

February pepper seedlings in the greenhousePhoto Kathryn Simmons
February pepper seedlings in the greenhouse
Photo Kathryn Simmons

Sow carrots #1 outdoors with indicator beets. Flameweed. Finish planting spinach, (direct sow if not enough transplants).

Buy seed potatoes mid-month and set out to greensprout (chit) before planting: 65°F (19°C) and light.

[Strawberries: plant new bought plants, if applicable.]

Late Feb, sow carrots # 2 (flameweed);

Really finish transplanting spinach. If needed, presprout 4oz/bed spinach for 1 week before sowing.

Till and sow areas for clover cover crops (eg grapes, eggplant beds), or oats, from 2/15.                    

Transplant fall-sown onions ½-3/4” deep, when no thicker than pencils. Weed over-wintered spinach, kale, collards.

In greenhouse sow broccoli #2 (2 weeks after 2nd), (shallots), lettuce #4, hoophouse cukes.

Perennials: Finish weeding. Give compost, if not done in fall, including strawberries and grapes.  See list for January.  Transplant bushes, canes, crowns if needed. Mulch. Finish pruning blueberries, ribes. Prune grapes before 3/21 – see last year’s log notes about replacement limbs needed, etc. Summer raspberries: cut out old canes. Install irrigation. Prepare sites for new grapevines, if needed.

Vates kale over-wintered Photo Twin Oaks Community
Vates kale over-wintered
Photo Twin Oaks Community

Harvest: (Chard?), collards, kale, spinach, leeks.