Fall is the time to start thinking about soil health, preventing erosion on bare soils and increasing organic material in your fields, gardens and other cropped areas. This article, courtesy of Osborne Seeds, covers the basic seed types to use for cover crops.
Cover cropping builds soils health by increasing organic matter which in turn can help drainage, retain soil moisture, increase nutrient availability and reduce erosion. Ideal planting dates will vary regionally but here in the PNW many growers will seed in the coming weeks. This means that some tough decisions will need to be made concerning which cover is right for you!
Below is a list of just some of the many benefits that each variety offers along with a quick reference (see table below) that shows seeding rates, hardiness and organic availability.
Cover Crop Quick Reference
Austrian Winter Pea
Cold hardy cover that provides a quick source of nitrogen with vines that incorporate easily into soil. Well seeded plots provide great weed suppression and make for an ideal forage crop supplying large amounts of protein. Rapid spring growth with the ability to produce large amounts of dry matter. Early blooms serve as great beneficial insect attractant.
This is a rough awned, two-row feed barley that serves as excellent weed suppression and erosion control! Winter barley produces large amounts of biomass and helps scavenge nitrates to reduce leaching with the possibility of roots reaching 6 feet. This economical cover has the ability to better handle salty soil compared to other cereals and puts biomass on faster too! Recent studies suggest that barley can aid in reducing incidence of leafhoppers, aphids and root-knot nematodes along with reducing weed pressures through allelopathic properties.
A winter annual in Western Washington and Oregon, crimson clover puts on fast growth in the fall and provides a great source of nitrogen with the possibility of 70-150 pounds per acre.
Crimson clover also provides great erosion control and can scavenge nitrates and reduce leaching. The beautiful dark red blossoms help attract beneficial insects and all-important pollinators.
A perennial along the West Coast and in the Midwest and Northeastern US. White clover has the ability to add large amounts of nitrogen to soils with the largest amount available from incorporation after its first season. White clover also performs well as living cover for permanent pathways and is ideal in orchards and vineyards and as forage for non-ruminants. Proper management can provide blossoms throughout the season and serve as a pollinator attractant when other beneficial plantings have finished flowering.
Fava Bean Diana
This winter or spring annual serves as a great nitrogen fixer with the ability to produce a 6-8 foot tall plant along with a 1-3 foot long tap root. The 3.5-4 inch edible pods can be used for human consumption or forage.
Fava bean Diana is very cold hardy with winterkill temperatures as low as 10 degrees Fahrenheit. Favas have the ability to continue to grow in cold wet conditions when other legumes go dormant. Favas are better able to tolerate low pH but will produce less nodules in heavily acidic soil.
A cool season, high yielding spring oat with the ability to survive through zone 8 in most seasons. This economical cover has the ability to produce large amounts of biomass, scavenge residual nitrates in soil to reduce leaching and can serve as a great forage crop.
Oats will perform best in cool moist conditions in well-drained soil. The quick germination of oats helps to provide great weed suppression along with allelopathic properties that inhibit weed seed germination.
Hardier than oats and triticale, rye provides great weed suppression, erosion control and scavenges nitrates to reduce leaching. This cover has the ability to perform even in less than ideal soil conditions and can help retain moisture for summer cropping. Rye has a fibrous root system and will recycle more nitrogen when planted earlier. Research shows that rye is effective in reducing small seeded weeds including lambsquarter and red-rooted pigweed and like the other cereals listed, it also has allelopathic properties. Harvest at boot stage for forage.
This mix combines the great nitrogen fixation of common vetch along with the superior biomass accumulation and nitrogen scavenging of rye to create a spectacular cover crop! Together these crops offer great weed suppression due to dense cover and the allelopathic properties of rye.
The viny habit of the vetch helps to weave the cover together to better protect against weeds, prevent erosion and hold in soil moisture.
A cross between wheat and rye, you can plant triticale earlier than rye to produce more fall growth. Triticale is winter hardy but slightly less than rye. It puts on less biomass in the spring which often allows for easier tilling compared to rye but still generates large amounts of organic matter. Its dense canopy and alleopathic properties make it a great weed suppressor and its extensive root system helps scavenge nitrates. Triticale’s high protein content make it an ideal forage crop.
This nitrogen fixing annual has a viny habit that has the ability to reach 2 feet in height with a tap root of 3-5 feet. Fall plantings in the Pacific Northwest generally flower in April and May and will provide the greatest nitrogen benefit when allowed to grow longer before incorporating.
Accumulated nitrogen from common vetch plantings can often account for half of nitrogen needed for summer crops that follow but exact amounts are dependent upon numerous factors.
Vetch provides great spring weed protection due to its extensive cover. It can be combined with cereal grains to scavenge nitrates to reduce leaching and serves as an early pollinator attractant.
Possible damping off interactions are possible after tilling vetch, growers should wait several weeks before seeding or transplanting following this cover. Unlike hairy vetch, common vetch does not have a hard seed coat.
More hardy than common vetch, hairy vetch is a hardy annual in some locations and a biennial in others. Hairy vetch has the ability to get the same height as common vetch and can have both smooth and hairy stems and leaves.
This nitrogen-fixer can produce tap roots up to three feet in length and has a little more tolerance to acidic soils compared to common vetch.
Hairy vetch is hard-seeded and tillage dates must be monitored closely to reduce weed issues in subsequent crops.
As is the case with common vetch, it is important to wait several weeks after tilling hairy vetch before direct seeding or transplanting of another crop.
Evaluate Before You Plant
Cover crops, like any other crops, will react differently based on specific environmental conditions and cultural practices. It is important to look at many different aspects of plant habit as well as future cropping systems in order to determine which cover crop is best for you.
If you would like to schedule a visit with a farm planner to talk about cover crops, fall soil tests, pasture management or other farm-related issues, please email firstname.lastname@example.org to request a free site visit. In many cases, funding is available for practices that protect water quality.
By Osborne Seed, reprinted with permission
Osborne Seed Company is a wholesale vegetable seed dealer in the Skagit Valley. Their customers are diverse ranging in size from market gardeners to large farms. They have a website (www.osborneseed.com), blog, and seed catalog.
Snohomish Conservation District does not endorse any particular seed company or dealer. This information is provided for educational purposes only.