Tag: last date to sow clovers

Focus Cover Crops for October: Winter Wheat and Austrian Winter Peas

In August I wrote about cover crops such as millets, southern peas, buckwheat which are frost-killed. For most of us in the mid-Atlantic, it’s too late for those.

October is too late to sow winter-killed cover crops in central Virginia

Our average first frost is October 14-20. If yours is later, and you still have 40-60 days to your average first frost, you can still sow oats to winter-kill. If possible add a legume (soy and spring peas are easy, and will be killed by the frost, so they won’t complicate food crops next year). For us, the cut-off date for oats is September 15 if we really push it. Sowing too late means you don’t get enough growth in the fall, and the soil is not adequately protected from erosion or from weed growth.

Oats winterkill completely at 6°F (-17°C) or three nights at 20°F (-7°C. Fall-sown barley (Hordeum vulgare), grows even faster than oats, and dies at 17°F (-8°C).

There are still three weeks here when it is worthwhile to sow cover crops (up to a month past first frost), and I’m going to write about those here.

See Planning Winter Cover Crops, a post that includes my Short Simple Guide to Winter Cover Crops and my slideshow Cover Crops for Vegetable Growers. Oats, barley, wheat and rye sown too early can head up and seed before you get to winter, making them less useful, and more of a weed problem. Once we’ve reached mid-October, this is no longer an issue here.

Winter-hardy grass cover crops to sow in October

Winter rye and winter wheat can be sown in the mid-Atlantic in October. Wheat has less of an allelopathic effect on small seeds, the inhibition of germination that lasts three weeks after rye is turned under. Wheat doesn’t produce as much biomass as rye, so there’s the tradeoff. We sow wheat if the area is ready for cover crops 20-40 days before frost, allowing us to make faster use of those plots in the spring, compared to plots sown to rye.

Winter wheat prevents erosion, suppresses weeds, scavenges excess nutrients, adds organic matter, encourages helpful soil microorganisms, and the fine root system improves the tilth. It is less likely than barley or rye to become a weed; easier to kill than barley or rye; cheaper than rye; easier to manage in spring than rye (less bulk, slower to go to seed); tolerates poorly drained, heavier soils better than barley or oats.

The challenges of wheat are that it does not have good tolerance of flooding, and is a little more susceptible than rye or oats to insects and disease.

For us wheat is a good, trouble-free winter cover crop. The later it gets towards our cover crop cutoff date of November 15, the more likely we are to choose rye. Also, of course, if we have already used all our wheat seed! Winter rye is hardier than any other cover crop and can take later planting dates. More about Last Chance Cover Crop next month. Then I will also write about how to protect the soil over the winter if it is bare.

Austrian Winter Peas graphic

 

 

Secondary cover crops in October: Include legumes where possible

See my September post for more about the benefits of including legumes with winter cover crops grasses. Also how to inoculate legume seeds with the nitrogen-fixing bacteria. See Working with the time you have left for options if you are in another climate zone.

Another key to success with fall sown legumes is to sow early enough to establish before winter halts growth, and to plan not to need that plot next year until flowering time for that legume. If you have a legume that doesn’t reach flowering, it’s not the end of the world, you just get less nitrogen for your money, and won’t be able to supply all the N needs of the following food crop. Crimson clover flowers in central Virginia 4/16-5/2, most usually around 4/20. Austrian winter peas bloom at the end of April, and hairy vetch in early May.

October 15 (our average frost date) is our clover/peas watershed (legume-shed?). Before that date we use crimson clover; after it (until 11/8, 3 weeks after our average frost date) we sow Austrian Winter Peas, along with winter rye or winter wheat.

More about Austrian winter peas

Austrian winter peas can be sown later than other legumes.

• Hardy type of Field Pea. (Black peas)
• Winter-kill in zone 6, hardy in zone 7. Hardy to 0°F (-18°C). (Canadian/spring field peas are hardy to 10-20°F (-12° to -7°C))
• Can sow several weeks later than clovers
• Sow at least 35 days before first hard freeze (25°F/-4°C). In zone 7a, 8/10–11/8
• Optimum temperature for germination is 75°F (24°C), minimum 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
• High N-fixers – a good stand can provide enough N for the following food crop when incorporated
• They fix as much, or more, nitrogen 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 crops the next year
• 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 early spring

Cautions with Austrian winter peas

• 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.
• Seeds are large and heavy – high sowing rates (compared to clovers). Cost/area is fairly high, a little higher than vetches
• If you haven’t grown peas or beans on that plot for some years, inoculate the seed.
• Winter-killed in zone 6, at 0°F (-18°C). For the best chance of winter survival in cold areas, choose your sowing date to get plants 6-8″ (15-20 cm) tall before the soil freezes. (Hairy vetch is more cold-tolerant than AWP.)
• Sowing in a mix with a winter grain will improve cold weather survival by reducing soil freezing and heaving.
• May not do well if sown in spring – require a cold dormant spell.
• Not tolerant of flooding, drought, high traffic, salinity, heavy shade, long cold spring weather below 18°F (-8°C) with no snow cover, or hot (or even warm) weather.
• Do not regrow after mowing or grazing once blooming starts.
• Peas on their own do not add much organic matter to the soil – the vines break down quickly.
• 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.
• 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.
• Can also be host to Sclerotinia minor, Fusarium root rot and Ascochyta

More resources on Cover Crops

My book Sustainable Market Farming has a chapter on cover crops and many 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.