Yellow Sweet Clover growing in the Trials field
Planting cover crops is a powerful way to improve your soil. Cover crops perform a host of valuable functions like increasing soil organic matter, fixing nitrogen, breaking up compaction, suppressing weeds and preventing erosion. In this guide we’ll discuss your options for fall cover crops and the benefits of each, when and how to plant, and how to manage the crop once it’s established. While commercial growers typically use a seed drill or mechanical broadcaster to plant cover crops (followed by mowing and tilling before the crop sets seed), home gardeners can grow cover crops too. For gardeners we recommend planting most cover crops by hand-broadcasting seed over freshly turned soil, then raking in lightly just before a rain. Before the mature crop sets seed, it should be cut with a scythe or mower, then left as mulch for the rest of the season or turned under with a rototiller. Because of the nutrients bound up by the decomposing crop, it is recommended to wait 2-3 weeks after tilling before planting another crop into the area. At this point the cover crop residues will have mostly decomposed, making organic matter and nutrients available to the next crop. Crimson Clover - Re-seeding annual hardy to Zone 5 Benefits: fixes nitrogen, builds soil, prevents erosion, attracts beneficials, tolerates shade, winter-killed residue is easy to manage in spring Uses: soil builder, ground cover, undersown in existing crops, insectary, hay and forage When to sow: 6-8 weeks before the average first frost, by end of July in cold climates Seeding rate and depth: 15 to 18 lbs/acre drilled, 22 to 30 lbs/acre broadcast, ¼-1/2” deep How to harvest: Allow to winter-kill in cold climates and till in residue in spring, or mow and till in before seed set in spring Limitations: does not tolerate heat well; growers in the South should plant in late summer/fall for overwintering to avoid heat-induced seed set Field Peas - Annual Benefits: fixes nitrogen, builds soil, decomposes quickly, edible tops Uses: soil builder, edible tendrils, forage crop When to sow: 6-8 weeks before first frost Seeding rate and depth: 5 lbs/1,000 sq ft or 200 lbs/acre, 1 ½ to 3” deep How to harvest: Winter-kills at 15ºF or till in when flowering begins Limitations: does not tolerate hot, dry conditions; growers in the South should use as fall/winter crop in areas where legumes have not been grown recently TIP: Oats support weak pea stems and act as a “nurse” crop; sow 120 lbs of peas with 2 bushels of oats per acre   Hairy Vetch - Perennial Benefits: fixes nitrogen, suppresses weeds, tolerates poor soil, adds 3-4,000 lbs of organic matter/acre Uses: soil builder, ground cover, nitrogen source, early weed suppression When to sow: 30-45 days before first fall frost for use as a winter annual; by end of July if mowing in fall for winter-killed mulch Seeding rate and depth: Drill seed at 15 to 20 lbs/acre, broadcast 25 to 30 lbs/acre or more if later in the fall or in challenging conditions, ¼-1/2” deep How to harvest: Re-grows vigorously in spring; roller crimp or mow and till under when 50-75% of flowers are in bloom Limitations: Requires consistently moist, well-drained soil for establishment – not suitable for planting in the driest parts of the Western U.S. Crimson Clover may be more practical in the Deep South.   Improved White Clover - Perennial Benefits: fixes nitrogen, reduces compaction, improves soil health, tolerates mowing/trampling/wet soils/drought Uses: soil builder, excellent for paths and lawns, undersown around existing crops for living mulch, green manure, hay, pasture forage When to sow: Preferably before a rain and at least 40 days before first fall frost Seeding rate and depth: ¼ lbs/1,000 sq ft, 5-9 lbs/acre drilled, 7-14 lbs/acre broadcast then rolled, raked or cultivated to ensure good soil contact How to harvest: Chisel or moldboard plow to kill; regular mowing to maintain Limitations: Slow to establish, not ideal for smothering weeds, prefers humid, cool, shady conditions for establishment TIP: Inoculant must be used if growing in Zones 8 and warmer but is not necessary in cold climates   Medium Red Clover – Perennial hardy to Zone 4 Benefits: fixes nitrogen, mines nutrients & conditions soil, tolerates shade, reduces compaction, attracts beneficial insects, tolerates poor/wet/acid soils, produces 2-4 tons dry matter/acre in 2nd year Uses: soil builder, ground cover, undersown in existing crops, insectary, hay and forage When to sow: Preferably before a rain and at least 40 days before first fall frost, when soil is above 41ºF Seeding rate and depth: Broadcast, drilled 1/2 lbs/1,000 sq ft or 10-15 lbs/acre, ¼-1/2” deep How to harvest: Incorporate once blooming begins in spring of 2nd year by mowing and/or tilling under Limitations: Slow to establish; not exceptionally heat-tolerant - growers in the South should plant in late summer/fall for overwintering   Oats - Annual Benefits: fast grower, prevents erosion, thick mulching cover suppresses weeds, scavenges nutrients, produces 8,000 lbs/acre dry matter from spring stands Uses: soil builder, nurse crop for legumes such as vetch or peas, green manure, grain, hay When to sow: At least 40-60 days before first fall frost, when soil is at least 38ºF. Proper timing is critical for good spring cover. Seeding rate and depth: Broadcast or drill 4 lbs/1,000 sq ft or 100-140 lbs/acre 1” deep. If broadcasting for thick winter-killed mulch, use highest rate (3-4 bushels per acre). How to harvest: Winter-kills in Zones 7 and colder. In warmer climates, graze, mow or till in when seedheads are just forming, or cut grain when seeds harden Limitations: Performs poorly in hot, dry weather; requires timely planting for best results   Annual Ryegrass - Annual Benefits: versatile, fast grower, suppresses weeds, controls erosion, adds organic matter, catches nutrients, thrives in all soil types Uses: soil builder, nurse crop for legumes such as peas and vetch, emergency forage When to sow: At least 40 days before first fall frost, when soil is at least 40ºF. Sow in fall in warm climates. Seeding rate and depth: Broadcast 20-30 lbs/acre or drill 10-20 lbs/acre, ½” deep How to harvest: Allow to winter-kill, or disk, till or plow under as soon as flowers form Limitations: Occasionally some plants overwinter and become weedy if allowed to set seed   Winter Rye - Perennial Benefits: fast grower, suppresses weeds, controls erosion, adds organic matter, catches nutrients, thrives in all soil types Uses: soil builder, nurse crop for legumes such as peas and vetch, emergency forage When to sow: From late summer to fall in Zones 3-7; in late fall or winter in Zones 8 and warmer (20-40 days before first fall frost, when temperatures are at least 38ºF). Seeding rate and depth: Drill 60 to 120 lbs/acre (1 to 2 bushels) into a prepared seedbed or broadcast 90 to 160 lbs/acre (1.5 to 3 bushels) and disk lightly, cultipack or roll to ensure good soil contact. Do not plant more than 2” deep How to harvest: Different methods must be used to kill rye depending on the growth stage:
  • Disk and plow under as soon as soil can be worked in the spring to avoid N tie-up
  • Mow or chop, then disk or till in when plants are between 12 and 20” tall
  • Mow or roller-crimp when plants have just begun flowering and are at least 24” tall.
Limitations: Overwinters and grows vigorously in spring; may be difficult to kill with tillage.   Tillage Radish - Annual Benefits: strong weed suppression, rapid growth, nutrient scavenging, lightening soil, reducing compaction Uses: breaking up hardpan, lightening soil, suppressing weeds and pests When to sow: Sow at least 4-10 weeks before the first fall frost Seeding rate and depth: Drill 8-12 lbs/acre or broadcast 12-15 lbs/acre How to harvest: Winter-kills in cold climates; in warmer regions mow, flail, or till in before the crop finishes flowering in spring Limitations: Does not tolerate waterlogged soil   Yellow Sweet Clover - Biennial Benefits: nitrogen-fixer, mines nutrients from deep in soil, drought-tolerant, attracts beneficials, tolerates poor soil, adds up to 2.5 tons dry matter/acre in first year Uses: excellent green manure, soil builder, subsoil aerator, and honey plant When to sow: Sow at least 6-8 weeks before first fall frost, when soil is at least 42ºF, by late August in the Northern Plains and through late summer in mild-winter areas. Seeding rate and depth: Broadcast ½ lbs/1,000 sq ft or 6-10 lbs/acre, drill 4-8 lbs/acre, ½” deep How to harvest: Be prepared for explosive 2nd year growth. Kill in spring by mowing or tilling when stalks are 6-10” tall for maximum N contribution, or at 12-24” tall for more organic matter contribution. Can be killed by mowing after flowering; however plants may be 8’ tall at this point with woody stems. Do not allow to set seed as seeds may remain viable without germinating for 20 years. Limitations: Does not tolerate waterlogged soil   Field Peas/Oats Mix - Annual Benefits: versatile, fixes nitrogen, builds soil, suppresses weeds, winter-killed mulch decomposes quickly, edible pea tendrils Uses: versatile soil builder, marketable pea tendrils, forage crop When to sow: At least 6-8 weeks before first fall frost, when soil is at least 38ºF Seeding rate and depth: Broadcast 5 lbs/1,000 sq ft or 200 lbs/acre and rake or cultivate How to harvest: Winter-kills at 15⁰F; in warm climates till under during flowering Limitations: Peas do not tolerate very hot dry weather   Field Peas/Oats/Vetch Mix Benefits: versatile, fixes nitrogen, suppresses weeds, spring residue decomposes quickly, edible pea tendrils, adds up to 8,000 lbs/acre of organic matter Uses: versatile green manure, soil builder, marketable pea tendrils, forage crop When to sow: At least 6 weeks before first fall frost; when soil is at least 38ºF Seeding rate and depth: Broadcast 6-8 lbs/1,000 sq ft or 210 lbs/acre and rake in How to harvest: Mow or roller crimp and till under once spring flowering has begun   Winter Rye/Hairy Vetch Mix - Perennial Benefits: fixes nitrogen, suppresses weeds, adds organic matter Uses: soil builder, weed suppression, reduces erosion, thick winter cover When to sow: 30-45 days before first fall frost Seeding rate and depth: Drill 60 lbs/acre (1 bushel) into a prepared seedbed or broadcast 90 lbs/acre (1.5 bushels) and disk lightly, cultipack or roll to ensure good soil contact. Do not plant more than 2” deep How to harvest: Mow or roller crimp and till under just after spring flowering