Cover Crops for Vegetable Growers
Newsletter articles
Early summer
Mid and late summer
Late summer legumes
Early fall
Fall
Early spring
Cover crop information
Annual
ryegrass
Buckwheat
Sudangrass
Mustard, spring
Mustard, fall (includes radish, rape, kale)
Red
clover
Hairy vetch
Oats
Wheat (includes spelt, triticale)
Rye
Research
Buckwheat
planting date
Buckwheat
field preparation
Fertility
Late-summer legume cover crops for overwintering
Red clover and hairy vetch
Late summer is one of the best opportunities vegetable growers have to establish a legume cover crop to supply the following year’s nitrogen needs. Late summer provides time for the legume to establish in the fall. Enough fall growth is needed for the plants to develop a strong root system and enough shoot growth to provide valuable winter cover. Most of the nitrogen is fixed during growth in May.
There are two legume cover crops that are both reliable and economical: medium red clover and hairy vetch. Red clover is normally spring seeded, but the easy availability, low seeding rate and high nitrogen fixation make it an attractive choice in the late summer as well.
Legume winter cover crops provide a great deal of nitrogen. If well managed, they can provide as much nitrogen to the next crop as fertilizer containing 100 to 150 lb/ac of nitrogen. Whether you are committed to raising all your nitrogen on the farm, or concerned about paying today’s high prices for nitrogen fertilizer, that nitrogen contribution looks attractive.
Choosing the legume
Hairy vetch is the best known winter legume for vegetable rotations in the mid-Atlantic region. It is at its northern limit in much of New York, but does very well. Medium red clover can be more versatile than hairy vetch, and more economical.
The decision of which legume to use is based on more subtle criteria.
If timing demands that the legume be overseeded into a vegetable crop at the time of the last cultivation, the choice must be red clover. It has the ability to establish in shade after broadcasting on the soil surface. Vetch seed needs to be drilled for reliable fall growth, and therefore best follows harvest and incorporation of the vegetable crop.
If the soil is dry, clover will have a better chance of establishing because it needs less moisture than the large-seeded hairy vetch.
If you raise small grain on the field, clover must be the choice. Hairy vetch has hard seed that will germinate in future small grain fields, and produce vetch seed that contaminate the grain.
If soil compaction is a problem, clover is preferred. Neither cover crop does well on compacted soil, but hairy vetch is more sensitive to the resulting waterlogging.
Nurse crop. Both of these legumes benefit from a nurse crop. Hairy vetch requires a nurse crop to reliably overwinter, and it is valuable for medium red clover as well. The nurse crop helps keep down weeds during their slow establishment, reduces winter kill and provides physical support that reduces matting under the snow and during spring growth.
A small-grain nurse crop should be sown at a low rate (approx 40 lb/ac). Wheat overwinters to provide support in the spring, especially for hairy vetch. It is likely the best choice for most situations. Oats die during the winter, allowing faster breakdown for earlier vegetable planting. Rye is the classic nurse crop with vetch, but it can be to be too vigorous for New York vegetable production. When sown in
Sowing
The cost of seed is $25-30 per acre for clover (15 lb/ac at $1.75 to $2.00) and $60 - $110 for hairy vetch (40 lb at $1.50 to $2.75/lb). Inoculum to insure nitrogen fixation costs $1.00 to $2.00 per acre. The grain seed adds $5 to $10 per acre. Clover and small grain seed of adequate quality for cover cropping can often be bought at a significantly lower cost from local farmers.
Hairy vetch is sown at 40 lb per acre. Vetch rates as low as 25 lb per acre work, but the additional weed suppression and nitrogen fixation from the higher rate make it attractive for vegetable growers. The small grain can be seeded at 40 lb/ac. If the grain seeding rate is too low, winterkill will be excessive. If it is too high competition will reduce vetch growth and nitrogen fixation. The vetch and grain seed can be mixed together in the drill.
Medium red clover is sown at 15 lb per acre. The seed can be broadcast onto prepared ground, or sown with a grass seeder. If overseeded into a standing crop by broadcasting, it is worth using 20 to 25 lb/ac. There are other red clovers available, but they don’t work nearly as well for this application.
The sowing time is mid-August through early September. Later seeding results in inadequate growth. Even within this window, earlier sowing improves winter survival, nitrogen fixation and weed control. The main cause of poor establishment of either crop is lack of moisture. New York usually receives adequate rain in late August and September for these crops to establish.
Spring management
In the spring, both crops are incorporated at early bloom (typically late May). Plan a rotation where vegetables are sown or transplanted in mid-June. This timing of incorporation maximizes nitrogen fixation, and minimizes both regrowth and volunteer seed. Bloom time is determined mostly by spring temperature, so the date will vary. Most of the nitrogen is fixed during the month of May, so premature incorporation costs a lot of nitrogen. In fact, if the field needs to go to vegetables in May it is not worthwhile to do a fall-seeded legume because so little nitrogen will be fixed. It would be more effective nitrogen management to have a vigorous overwintering cover crop that scavenges leftover nitrogen.
This article is intended for publication in Cornell Cooperative Extension newsletters, and similar outlets, that reach growers by early August.
