Late Season Cover Crops

There are many reasons to plant a late season cover crop. Generally, a cover crop will increase organic matter, improve soil structure, scavenge remaining nutrients, choke out weeds, and prevent soil erosion. There are several types of grasses, legumes, and brassicas that work well as winter cover crops, and each have their own strengths and weaknesses. Below we’ve described several good choices, depending on your specific goals and field conditions. These species do best when planted in late summer or early fall (see individual entries below for more details). While the fall planting window has extended, in some cases into November (!), remember that all cover crops are most effective when planted as quickly as possible following harvest.

Grasses

Grass cover crops can reduce erosion, absorb soil nitrogen (N), and produce a significant amount of organic matter. Kill grasses before maturity in the spring to ensure efficient decomposition. Mix grass species with a legume to reduce the C:N ratio and supply more N for the following year’s crop, or with any broadleaf species to increase weed suppression.

​​​​​Winter or cereal rye (Secale cereale) is the most common cover crop used by growers in Massachusetts. It is inexpensive, readily available, and easy to establish. November-planted rye is more practically thought of as a very-early-planted spring cover crop since it will grow little until the spring. In most areas of the state, rye is best planted before September 15 to recover the available N from the soil, produce enough canopy to outcompete weeds, and protect the soil from erosion. It consistently overwinters here and will continue to grow in the spring, producing up to 7,000 lbs/A of biomass to contribute to soil organic matter. It should be killed before the flowers emerge or be seeded with a legume to keep the C:N ratio low and prevent N tie-up . It can take several weeks and multiple tillage passes to break down in the spring, so it is best used in fields that will be planted into a late spring/early summer crop next year. Seeding rate: 90-120 lbs/A broadcast; 60-100 lbs/A drilled; 50-60 lbs/A mixed with a legume.

Annual or Italian ryegrass (Lolium multiflorum) and perennial ryegrass (Lolium perenne) are also gaining popularity in the Northeast. These grasses have dense root systems that outcompete weeds, protect against erosion, and are easy to incorporate in the spring. Annual ryegrass can tolerate some flooding. Perennial ryegrass is more cold-hardy but also harder to kill if it goes to seed. Both ryegrasses are good for interseeding since they are shade and traffic tolerant, but may not germinate very well under dry conditions. Plant 6-8 weeks before the fall frost date. The seed is small and light, so specialized equipment such as a Brillion seeder is needed to seed a large area. Seeding rate: 20-30 lbs/A broadcast; 10-20 lbs/A drilled; 8-15 lbs/A mixed with a legume.

Oats (Avena sativa) come up quickly and can be seeded in late summer. They are best planted before September 15, similar to winter rye. Unlike winter rye, oats will winterkill in Massachusetts, making for simpler field preparation in the spring. However, oats provide less weed control, lower organic matter contribution, and do not contribute N to the following crop in the spring. Mixing with an overwintering legume, such as hairy vetch, can produce N without the timing complications of killing a mixed cover crop stand in the spring. Seeding rate: 110-140 lbs/A broadcast; 80-110 lbs/A drilled; 60-90 lbs/A mixed with a legume.

Winter wheat (Triticum aestivum) is increasingly being used both as a cereal grain and as a cover crop. It is winter hardy, but does not grow as tall or mature as quickly as rye so there is less rush to kill it in early spring and risk compacting wet soils. Wheat is excellent for erosion control, scavenging N, P, and K, building soil organic matter, and improving tilth. For best results, plant it in late summer to early fall, before September 15. Best growth will be in well-drained soils with moderate fertility. Rye is a better choice on wet soils. Wheat works well as a companion crop for legumes, such as hairy vetch or crimson clover, because they all mature at a similar time in the spring. Seeding rate: 90-120 lbs/A broadcast; 60-100 lbs/A drilled; 60-90 lbs/A mixed with a legume.

Triticale (x Triticosecale) is a hybrid between wheat and rye and is particularly valued as a dual-purpose cover crop, which can be fed to livestock in the spring. It can be seeded as early as August or as late as late October and can produce more fall growth than winter wheat, providing more weed suppression and erosion control. Seeding rate: 90-100 lbs/A broadcast; 75-80 lbs/A drilled; 60-90 lbs/A mixed with a legume.

Legumes

Legume cover crops are a good choice if you are interested in adding N to the soil and reducing your nitrogen fertility bill. Legumes fix N from the air and store it in their leaves and then roots during the winter. That N is made available to plants when the legume is tilled in and starts to decompose in the soil. It's a good idea to inoculate seed with the appropriate N-fixing bacteria before planting. Bacterial inoculants are specific to closely related legumes (for cover crops, you'll most commonly see them separated into clover/alfalfa and pea/vetch groupings). Regular use of the same types of cover crops may establish bacterial populations in the soil but most growers add inoculants annually since they are affordable and essential to N fixation. If well-managed, legume cover crops can provide as much as 100-150 lbs N/A to the following crop.

Hairy vetch (Vicia villosa) benefits from growing with a nurse crop such as rye or wheat to help reduce matting during the spring and to keep weeds down. The vetch and the grain can be mixed together in the seed drill or broadcast seeder. A vetch + grass cover crop mixture retains more soil moisture than a grass planted alone. In the spring, incorporate vetch at early bloom, typically in late May. Vetch seeded in early August is less likely to survive the winter. With a good flail mower, vetch can be used in a reduced tillage system without matting and tangling in the equipment but care must be taken to avoid surviving vetch becoming a weed. Seeding rate: 25-40 lbs/A broadcast; 15-40 lbs/A drilled, 15-20 lbs/A mixed with a grass.

Red clover (Trifolium pratense) is a short-lived perennial that is somewhat tolerant of soil acidity and poor drainage. Mammoth red clover produces more biomass for plow-down than medium red clover but does not regrow as well after mowing. Mammoth will often establish better than medium red clover in dry or acidic soils. Sow in early spring or late summer. Red clover can be undersown in mid-summer into corn or winter squash before it vines, and into other crops such as fall brassicas if soil moisture is plentiful. Clovers germinate and grow slowly and so can be planted along with a faster-growing grass and/or peas as a nurse crop. Clovers are a good option to include in a field that won’t be planted into a cash crop for a full year or more. Seeding rate: 10-15 lbs/A broadcast; 6-15 lbs/A drilled; 6-10 lbs/A mixed with a grass.

Crimson clover (Trifolium incarnatum) grown as a winter annual should be seeded mid-August to early September in New England; seed it too early and it will make seeds in the fall. While it grows well in dry conditions, it may have trouble germinating. This clover is a better fall weed suppressor than hairy vetch. Crimson clover is easily killed by incorporation or can even be rolled or mowed in the spring at late-bloom stage for no-till operations. It will establish faster than other clovers. Seeding rate: 22-30 lbs/A (15-20 lbs/A in a mixture) broadcast; 15-18 lb/A (10-12 lbs/A in a mixture) drilled.

Balansa clover (Trifolium michelianum) is an annual clover with smaller seeds than crimson clover. It grows slowly in the fall and is best grown with a nurse crop like oats. Hollow stems make balansa clover more suitable for spring roller crimping than other legumes. It is less winter hardy than crimson clover and may not consistently overwinter in colder parts of the state. Seeding rate: 10-15 lbs/A broadcast; 6-15 lbs/A drilled; 6-10 lbs/A mixed with a grass.

Peas (Pisum sativum subsp. arvense) come in two main types: Austrian winter peas (black peas) and Canadian field peas (spring peas). Spring peas can be planted mid-August to mid-September in much of New England and winter peas should be planted from mid-September to mid-October. These peas fix N more quickly in dry conditions than white clover, crimson clover, or hairy vetch but winterkilled "spring" field peas will not produce a nitrogen credit for spring crops. Peas are susceptible to Sclerotinia so don’t plant them in a field with a history of white mold. Drill or incorporate seed 1-3 inches deep to ensure good soil moisture contact. Seeding rate: 80-120 lbs/A broadcast; 75-100 lbs/A drilled; 60-80 lbs/A in a mix.

Brassicas

Brassicas are used as cover crops for pest management or, in the case of the tillage radish, for improving water drainage and soil structure. Brassica cover crop species are susceptible to the same pests as brassica cash crops, so be sure to factor in any brassica cover crops that you plant when planning crop rotations for pest management.

Brown mustard (Brassica juncea) found in many of the ‘Caliente’ seed mixes is a biofumigant planted to combat root-knot nematode and a variety of soil-borne fungal pathogens, including Fusarium, Verticillium, Rhizoctonia, Pythium, and Phytophthora capsici. It is also allelopathic against weeds. If allowed to flower, this crop is highly attractive to honeybees. Successful biofumigation with this cover crop is achieved by following these steps:

1. Apply adequate fertility (50 lbs N/A and 20 lbs S/A).
2. Allow it to flower before incorporation.
3. Mow and disc or rototill under and roll or pack the soil immediately.
4. Irrigate after incorporation or incorporate before rain to enhance fumigation.

Plant brown mustard in late August through September. Seeding rate: 10-15lbs/A broadcast; 8-12 lbs/A drilled.

If any tillage is done after fall cash crops, it is essential to plant a cover crop, regardless of the type. Leaving a tilled field bare over the winter is very damaging to soil structure and will increase erosion and reduce long-term fertility. When a cash crop is growing into late October, it is best to interseed a cover crop earlier in the fall or plant a cover crop using reduced tillage since the cover crop will be too small to protect tilled soil over the winter. Though it may take several growing seasons or a lifetime to perfect the art of cover cropping, your soil will thank you.

Resources:

• Northeast Cover Crops Council Cover Crop Explorer and Species Selector Tool.
• A Comprehensive Guide to Cover Crop Species Used in the Northeast United States. Prepared by USDA-NRCS.
• Managing Cover Crops Profitably. 3rd ed. Published by the Sustainable Agriculture Network, Beltsville, MD.
• Cover Crop Plant Guides prepared for USDA by NRCS, RMA and FSA.
• Cover Crop Chart prepared by USDA-ARS.