Five cover crops to try this fall after vegetables

A grass/legume cover crop mix in Waseca, MN.
Photo: Annie Klodd

The time has come to shop for fall-planted cover crops to sow after vegetable harvest. Fall cover crops benefit vegetable production in numerous ways, including soil building, erosion control, weed suppression, and nitrogen fixation.

Certain species will overwinter into the spring, while other non-winter hardy species are meant to be terminated naturally with the first killing frost of the fall. Each species has unique traits and benefits, and species can be planted in mixes or “cocktails” to combine the benefits of each. Here are 5 popular cover crops to try this fall for vegetables:

Winter rye (cereal rye)

Winter rye is one of the most cold-hardy cover crops for Minnesota, which contributes to its popularity as a winter cover crop. This high biomass species not only contributes large amounts of organic matter and provides erosion control, but is also a top pick for weed suppression due to its tall canopy and rapid establishment.

Winter rye in early spring, out-competing dandelions.
Photo: Robin Trott

How winter rye manages weeds: First, the disturbance caused by fall planting competes with newly emerged winter annual weeds in the fall. Then, it germinates and grows rapidly, continuing to out-compete weeds for space and soil resources. If it is allowed to grow for several weeks into the spring, it can also shade out early summer annual weeds like lambsquarter and ragweed.

Plant winter rye by mid-October, not later than three weeks before the first killing frost. However, research in multiple states has shown that planting earlier in the fall (September to early October) allows it to accumulate more biomass and better out-compete weeds in the spring.

Recommended seeding rates are between 55-100 lbs per acre, but higher seeding rates are recommended when weed suppression is a primary goal.

Tillage Radish

Tillage radish in a cover crop mix with other species.
Photo: Annie Klodd

Tillage radish (also called forage radish) has a long taproot that penetrates hard soil, breaking up compacted areas and adding organic matter. While it is not winter-hardy, it can be planted in the late summer and grown for several weeks until the first killing frost.

If they are not tilled under, the large leaves of tillage radish will remain on the field through the winter and may provide a physical barrier to early weed emergence. Planting dates range from July 25 to September 15.

The recommended seeding rate is 5 to 15 pounds per acre, or less if used in a multi-species mix.

Austrian Winter Pea

Austrian winter pea is a legume planted in the early fall and terminated by winter. It provides available N (between 90-150 pounds per acre) and organic matter to the soil. The stems break down quickly after termination, releasing available N more rapidly than some other species.

Austrian winter pea prefers cool weather, with an ideal planting time of early fall. Plant at 30-90 pounds per acre.

Red Clover

A fall-planted red clover/rye cover crop mix in spring.
Photo: Annie Klodd

Red clover adds a moderate amount of N, breaks up heavy soil, and improves soil structure and organic matter content of the topsoil. Plant alone or in a mix with other species in order to combine benefits. It is mostly winter hardy in USDA Zone 4, and is adapted to a wide range of soil types compared to other clovers. More information on red clover can be found here.

For a winter cover crop, plant red clover in late summer or early fall at a rate of 8-12 pounds per acre. Terminate it in the spring before vegetable crop planting.

Triticale

Triticale is another high biomass, winter-hardy grass cover crop used for weed suppression, organic matter addition, and erosion control. It overwinters well in Minnesota and should typically be terminated at least 2 weeks prior to vegetable crop planting in spring.

Triticale should be planted at 40-60 pounds per acre, between August and October.

Spring termination of large cover crops:

Fall-planted winter rye in May, before crop planting.
Photo: Annie Klodd

Growers are generally advised to terminate high biomass cover crops at least 2-3 weeks prior to vegetable planting to avoid competition.

While terminating close to planting time allows prolonged weed suppression, it also may cause unwanted competition with the vegetable crop, through uptake of soil nutrients and water. Depending on the season, this may mean that spring-terminated cover crops are best utilized before warm-season vegetables or late-planted cole crops, to allow time for the cover crop to grow before termination.

Growers wishing to experiment with late termination or planting green should try it on a small scale first. Results may vary substantially between years and crops.

Author: Annie Klodd, Extension Educator - Fruit and Vegetable Production