Spring Planted Cover Crops for Vegetable Rotations

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

One principle of managing for improved soil health is that you should always have a crop growing on the soil. This will maintain or add organic matter, provide benefits from the action of growing roots, and recycle nutrients.

Where fall cover crops were not planted due to late harvest, spring cover crops can be planted and provide soil health benefits where vegetables are not scheduled until late May or the month of June.

The most common grass family cover crop options for mid to late March or early April planting are spring oats, and annual ryegrass. Plant oats 90-120 lbs per acre and annual ryegrass at 20-30 lbs per acre.

Mustard family (Brassica) cover crop options for late March or early April planting include yellow mustards, white mustards, brown mustards and oriental mustards. Companies also offer blends of several mustard species. Mustards are generally planted at 10-20 lbs per acre. Rapeseed and canola are another mustard family option for spring planting at 5-12 lbs per acre. Forage radishes and oilseed radishes can also be spring planted at a rate of 4-10 lbs per acre. Arugula is an additional mustard family option planted at 4-7 lbs per acre.

In the legume family, field peas are another option for spring planting. One type of field pea is the winter pea which is often fall planted in our area but can be spring planted. It has smaller seed so the seeding rate is 30-60 lbs per acre. Canadian field peas are larger seeded and used as a spring cover crop planted alone at 120-140 lbs per acre. An often-forgotten spring seeded legume crop that can also be used is red clover. Red clover can be frost seeded into small grains, seeded alone, or mixed with spring oats or annual ryegrass. Seeding rates for pure stands would be 10-16 lbs per acre, for mixtures 6-10 lbs per acre.

Mixtures also can be used. Research has shown that you get the best soil health benefits from mixing three species from different plant families. Commonly a grass is mixed with a legume and with a mustard family crop. Examples would be spring oats, field peas, and forage radish; or annual ryegrass, red clover, and mustard. Reduce seeding rates of each component when using in mixtures. Companies often offer preblended mixture for these uses.

Many of the mustards have biofumigation potential. When allowed to grow to early flower stage and then incorporated into the soil, they release compounds that act as natural fumigants, reducing soil borne disease organisms. Some biofumigant mustard varieties include Pacific Gold, Idagold, and Kodiak. Biofumigant blends include Caliente and Mighty Mustard. Biofumigant rapeseed varieties include Dwarf Essex and Bonar.

To use as a biofumigant, mustards will be allowed to go to full growth (early flowering) and then are chopped with a flail chopper (cut fine) and incorporated with a tractor mounted rototiller or other tillage tool for complete incorporation. Chopping releases the biofumigant compounds in the plants. Ideally the area then should be rolled with a cultipacker or overhead irrigated to seal in the biofumugant.

Finely chopped biofumigant cover crop ready for incorporation. Chopping releases the biofumigant compounds in the plants.

When used as a biofumigant, mustards should be grown as a crop. You need to add 60-100 lbs of nitrogen per acre to produce the maximum biomass. Nitrogen is also required to produce spring oats and annual ryegrass at similar rates. When planting mixtures with peas, nitrogen rates should be reduced.

Several spring-planted cover crops have been used specifically to address nematode infested soils. This includes “Nemat” arugula and “Image” radish. Mustards such as Caliente 199 have been used to reduce Phytophthora infestations.

Spring planted cover crops shown including mustards, rapeseed, radishes, and arugula.