Gordon Johnson, Extension Ag Agent, Kent Co.; gcjohn@udel.edu
Vegetable growers should make plans to put in late summer or fall cover crops after summer vegetables are harvested. Cover crops help to maintain organic matter, recycle nutrients, reduce compaction, and maintain overall soil health. These benefits far outweigh the cost of establishing the cover crops.
The following are some cover crops to consider:
Winter Annual Legumes
These cover crops will produce significant biomass (organic matter) and, at the same time, provide nitrogen for the following crop through biological nitrogen fixation: hairy vetch, crimson clover, field peas (winter peas). Hairy vetch makes an excellent mulch for no-tilling vegetables into. Plant by September 30.
Small Grains
These winter annual grasses will provide significant biomass, recycle nutrients (especially nitrogen), and produce excellent mulch for no-tilling vegetables in the spring: rye, triticale, wheat, barley, winter oats. Spring oats can be used where you want to get fall cover but need the crop to winter kill for early spring vegetable crops. Plant by the end of October.
Mustard Family Cover Crops
These include both fully hardy overwintering species and species that will winter kill. They provide significant organic matter, recycle nitrogen, can reduce compaction, and offer the potential for biofumigation. Plant by September 15. Included are:
Rapeseed and Canola – overwinter and are good biofumigants
Forage Radish, Oilseed Radish, and Daikon Radish – very good for reducing compaction in soils; forage radish winter kills, oilseed radish is more hardy
Mustards (brown and yellow mustards as well as garden mustard) – offer good biofumigant potential; half hardy
Turnips (forage and garden types) – good biomass production; half hardy
Kale (forage and garden types) – winter hardy; good biomass production
Hybrid Forage Brassicas (such as ‘Typhon’) – these are hybrid crosses of two or more species that will produce excellent fall growth and some will overwinter
Annual Ryegrass
This winter annual grass offers easy establishment, even when overseeded, and puts on significant fall and spring biomass. It scavenges nitrogen and is a quick decomposer in spring. Plant by October 15.
For seeding rates, contact you County Extension Office.
It is often advantageous to plant several of these cover crops together and most will mix well. Use the planting deadline for the species that has to be planted the earliest. Reduce the rate of each component in the mix by 1/3 to ½. I particularly like a rye-hairy vetch-crimson clover mix.