Cover crop selection for vegetable growers

Oats (Avena sativa)

• Pros: Oats are easy to find and affordable. They are nitrogen scavengers, they prevent erosion, and they provide weed control. The residue breaks down quickly in the spring to allow for early season plantings.
• Cons: Nitrogen, erosion fighting, and weed suppression benefits may be slightly less than overwintering cereals, but are still quite good.
• Notes about oats: Fall planted oats mix well with peas and berseem clover.

Peas (Pisum sativum)

• Pros: Peas provide moderate nitrogen fixation and scavenging. They mix well with oats and can be planted a bit later in the fall than clovers. They break down quickly in the spring to allow for early spring crops. 
• Cons: Peas can be a crop rotation problem if you plan to plant peas in the same field the following spring. Despite flowering, peas do not attract many beneficial insects, and they may attract thrips.
• Notes about peas: Peas mix well with oats and other cereals.
  • The most common peas used as cover crops are yellow (white flowers) or speckled (pink flowers) field peas.
  • Austrian winter peas are another type of peas that are gaining popularity due to their hardiness, but they are not hardy enough to consistently survive winter in Minnesota.

Berseem clover (Trifolium alexandrinum)

• Pros: Berseem clover is an excellent nitrogen fixer that prevents erosion and outcompetes weeds a bit better than peas. They break down quickly in the spring to allow for early spring crops. 
• Cons: Berseem clover dies at around 20°F compared to peas, which die at around 10°F, so it needs to be planted earlier in the season.

Tillage radish (Raphanus sativus)

• Pros: Tillage radish breaks up compacted soils. They are easy to find and affordable. They can also help to control nematode populations. They break down quickly in the spring to allow for early spring crops.
• Cons: Tillage radish can pose a rotation problem when grown in fields where you plan to plant other Brassicas due to disease issues. 

Sugar beet (Beta vulgaris, Altissima group)

• Pros: Sugar beets can break up compacted soils.
• Cons: Sugar beet seed may be harder to find. Sugar beets need a bit more warmth to establish, so they should be planted earlier than tillage radish. Crop rotation could be a problem for growers who grow beets and spinach. 

Winter wheat (Triticum aestivum)

• Pros: Winter wheat tends to be more affordable than winter rye, and it’s easier to manage in the spring. It is an excellent nitrogen scavenger and provides good weed suppression and erosion control.
• Cons: Winter wheat has to be planted a bit earlier than rye, and it tends to put on less biomass in the fall. It has a high carbon to nitrogen ratio unless mixed with a legume.
• Notes about winter wheat: Terminate when flowering begins, and allow 3 weeks for breakdown to avoid tying up nitrogen.

Winter rye (Secale cereale L.)

• Pros: Winter rye is very hardy, and can be established late in the season (see Midwest Cover Crop Council Decision tool for exact dates in your county). It provides excellent weed suppression and nitrogen scavenging. The deep roots help to break up compacted soil and prevent erosion.
• Cons: Winter rye can be hard to kill, and is known to form a thick mat at termination. It has a high carbon to nitrogen ratio unless mixed with a legume.
• Notes about winter rye: In organic or herbicide-free systems, terminate by mowing when flowering begins.
  • Mowing earlier may result in regrowth. Using a sickle bar mower instead of a flail mower can help to prevent it from forming a thick mat.
  • If you are using herbicides to terminate winter rye, spray when it is somewhere between 4-8 inches tall. Spraying works best under warm conditions when plants are actively growing.
  • Some growers terminate rye and leave it on the field as a mulch, especially with pumpkins growing on sandy soils. Leaving rye on the field as mulch in heavier soils can lead to moisture problems. If incorporating, allow 3 weeks for breakdown to avoid tying up nitrogen (especially if the rye is terminated later in development when the carbon to nitrogen ratio is higher).

Hairy vetch (Vicia villosa)

• Pros: Vetch provides substantial nitrogen and moderate weed suppression. 
• Cons: Vetch is slow growing in the fall (but grows quickly in the spring). It can be difficult to terminate and its vine-like growth habit can make the mulch difficult to manage
• Notes about vetch: Vetch grows well with winter wheat or rye. If planted too late in the season, it will not survive the winter. Vetch may become a weed, however, as the seed can survive for several years, glyphosate alone is not reliable for chemical termination, and vines are difficult to kill mechanically.

Red clover (Trifolium pratense L.)

• Pros: Red clover provides substantial nitrogen and great weed suppression. Its deep roots can help to break up compacted soil, and its flowers attract beneficial insects if allowed to flower in spring. It can also be frost seeded.
• Cons: Red clover is slow to establish in the fall. 
• Notes about red clover: Terminate when flowering begins, not before, if relying on mechanical methods for termination.

Oats (Avena sativa)

• Pros: Oats are easy to find and affordable. They are nitrogen scavengers, they prevent erosion, and they provide weed control. The residue breaks down quickly in the spring to allow for early season plantings.
• Cons: Nitrogen, erosion fighting, and weed suppression benefits may be slightly less than overwintering cereals, but are still quite good. 
• Notes about oats: Mixes well with peas and other legumes. Can be terminated at any point. Growers do not need to wait until flowering, as they would with wheat or rye. 

Spring barley or wheat (Hordeum vulgare and Triticum aestivum)

• Pros: Spring barley and wheat help to scavenge nitrogen in the spring, prevent erosion, and outcompete weeds. 
• Cons: If using mechanical methods to terminate, planting might be delayed slightly while waiting for anthesis (flowering). High carbon to nitrogen ratio unless mixed with a legume.
• Notes about spring barley and wheat: Wait until it begins to flower to terminate if relying on mechanical methods like disc tillage for termination. Herbicides are effective at any point.

Annual ryegrass (Lolium multiflorum)

• Pros: Annual ryegrass is quick to establish. It serves as a nutrient catch crop, it’s easy to incorporate, and is about half the price of winter rye.
• Cons: Annual ryegrass can become a weed if it goes to seed.

Red clover (Trifolium pratense L.)

• Pros: Red clover can be frost seeded for early establishment. Seed tends to be affordable.
  • Red clover provides excellent nitrogen fixation and erosion prevention.
  • It outcompetes weeds better than other legumes, and deep roots help to break up compacted soil.
  • It also attracts beneficial insects if allowed to flower.
• Cons: Red clover can be tricky to terminate, and can become weedy if grown on its own.
• Notes about red clover: Terminate when flowering begins, not before. Improve weed suppression by mixing red clover with a cereal.

Crimson clover (Trifolium incarnatum)

• Pros: Crimson clover provides substantial N fixation.
  • It mixes well with rye and wheat, provides some weed suppression.
  • It may attract some beneficial insects including pollinators and natural enemies if allowed to flower before termination.
• Cons: Crimson clover can become weedy if grown on its own.
• Notes about crimson clover: Improve weed suppression by mixing red clover with a cereal. Plant clover before grasses so that the grass doesn’t overtake the clover.

Peas (Pisum sativum)

• Pros: Peas provide moderate nitrogen fixation and scavenging. They mix well with oats and can be planted as soon as the ground is ready for planting in spring.
• Cons: Peas can be a crop rotation problem if you plan to plant peas in the same field the following fall or spring. Despite flowering, peas do not attract many beneficial insects, and they may attract thrips.
• Notes about peas: Peas mix well with oats and other cereals. Growers can choose between yellow (white flowers) and speckled (pink flowers) field peas, or Austrian winter peas.

Buckwheat (Fagopyrum esculentum)

• Pros: Buckwheat is quick to establish and provides excellent weed suppression.
  • The flowers attract pollinators and natural enemies.
  • For a non-legume, it has a relatively low carbon to nitrogen ratio (~24:1 at maturity), and so it breaks down quickly to allow for the next crop.
• Cons: It goes to seed quickly, and so it must be mowed or terminated at flowering to prevent re-seeding. Some research shows that buckwheat may attract thrips.

Sudex / Sorghum sudangrass (Sorghum bicolor x Sorghum sudanense)

• Pros: Sudex is an excellent source of organic matter and weed suppression.
  • Its deep roots can break up compacted soils.
  • This crop thrives in hot summer weather.
  • Sudex can be grazed multiple times if growers are incorporating livestock onto their farms (take care to avoid food safety risks and only graze a field that will not be re-planted with a food crop until the following year).
• Cons: Sudex may require irrigation for good establishment, especially in sandy soils. Due to the abundance of biomass and high carbon to nitrogen ratio, it can be difficult to terminate without equipment and takes some time to break down.
• Notes about sudex: Sudex works best in fields that will remain fallow until the following spring.
  • It should be mowed when it reaches 3-4 feet to encourage deep root growth.
  • Due to the abundance of biomass produced and the structure of the crop, it is likely to outcompete other plants in a cover crop mix unless added to a mixture at a low rate.

Sunflowers (Helianthus spp.)

• Pros: Sunflowers are native to Minnesota.
  • They attract natural enemies including predatory hemipterans and parasitoids.
  • They also produce substantial biomass for growers who wish to build organic matter.
  • Some growers have used sunflowers for agritourism, depending on stand size and grower interest.
• Cons: Sunflowers are a long-season crop (~75 days to flower).
  • If grown as a cover crop, sunflowers may not flower in time to attract the insects listed above, depending on planting and termination dates.
  • Sunflowers do not provide good weed management on their own.
• Notes about sunflowers: Sunflowers can be underseeded with a ground cover like oats to provide better weed management.

Buckwheat (Fagopyrum esculentum)

• Pros: Buckwheat is quick to establish and provides excellent weed suppression. The flowers attract pollinators and natural enemies, and it tolerates heat well. 
• Cons: It goes to seed quickly, and so it must be mowed or terminated at flowering to prevent re-seeding. Some research shows that buckwheat may attract thrips. 
• Notes about buckwheat: Buckwheat has a relatively short growing window (45-50 days), and is a good crop for growers who wish to plant an early spring crop as well as a late fall crop with a cover crop in between. Research results about buckwheat as a summer cover crop are mixed — in some years it works well, and in others, cold fall weather prevents a successful second crop. 

Lacy phacelia (Phacelia tanacetifolia)

• Pros: Phacelia flowers are extremely attractive to pollinators; they support both honey bees and native bees, including bumble and solitary bees. Phacelia produces substantial biomass and provides good weed suppression.
• Cons: Phacelia may attract plant bugs such as the tarnished plant bug (Lygus lineolaris).

Cowpea (Vigna unguiculata)

• Pros: Cowpeas are drought tolerant and establish well in heat. They provide nitrogen via nitrogen-fixation and attract beneficial insects. Their deep roots can help to break up compacted soil.
• Cons: Cowpeas are not sufficient for weed control on their own, but work well in mixes with Sudex (low rate of Sudex) or buckwheat.
• Notes about cowpeas: Chose a variety bred for leafy green vegetation vs. seed for more organic matter contribution.

White clover (Trifolium repens L.)

• Pros: White clover is very hardy once established, and tolerates foot traffic. It is a perennial and a nitrogen fixer.
  • Its low-growing habit makes it a good choice for footpaths.
  • If allowed to flower it provides nectar to pollinators.
• Cons: White clover can be slow to establish, and usually requires a nurse crop (see below).
  • It can creep into rows, so bed edges must be hoed or cultivated regularly.
  • On its own, it is not known to be a great weed suppressor, so it should be combined with a grass for optimal weed management benefits.
• Notes about white clover: White clover does best when planted with a quick-growing grass nurse crop. Planting with a grass will also help with weed control.
  • It can be terminated and re-seeded each year or maintained as a perennial in permanent beds.
  • Seed at the time that you plant your beds, not before, to reduce foot traffic as it is establishing.
  • White clover is not hardy in far northern Minnesota.

Oats (Avena sativa)

• Pros: Oats are quick to establish and provide good weed control. As a nurse crop, oats support clover by keeping weed pressure low as the slower-growing clover becomes established.
• Cons: Oats are annuals and will not survive the winter. This may be a pro or a con depending on the system. For permanent beds, a fescue (see below) might be a better choice.

Annual ryegrass (Lolium multiflorum)

• Pros: Annual ryegrass is quick to establish and provides good weed control. As a nurse crop, it supports clover by keeping weed pressure low as the slower-growing clover becomes established.
• Cons: More expensive than oats.

Fine and tall fescues

• Pros: Fescues are relatively low-maintenance turf grasses that require infrequent mowing. Fescues are winter hardy and tolerant to foot traffic as well as equipment traffic, and so they make good perennial living rows.
• Cons: Fescues are much more expensive than other cereals used for cover crops, and so they are not very practical for annual systems where beds are remade each year. They are a bit slower to establish than spring cereals like oats and ryegrass.
• Notes about fescues: Fine fescues are a group of grasses that includes creeping red fescues, Chewing fescue, hard fescue and sheep fescue. These are often used as low-maintenance lawn grasses.
  • Tall fescues are a bit more tolerant to traffic. Both will tolerate foot traffic, but tall fescues will do better with equipment traffic. Adjust your mixture of fine to tall fescues based on anticipated traffic.
  • Fine and tall fescues perform well in mixtures with clover. They are typically sold as turfgrass seed rather than cover crop seed.
  • The turfgrass team maintains a list of places to source fescue seed.