Cover Crop

A garden bed left bare is a bed losing soil. Wind, rain, and ultraviolet sunlight all degrade exposed soil; weed seeds colonize unprotected ground; soil biology starves without root exudates to feed it. The cover crop’s job is to keep the bed working — covered, rooted, alive — when no harvestable crop is in it.

What cover crops do

• Cover the soil — physical protection from wind and rain erosion; reduce surface temperature swings; preserve moisture
• Build organic matter — when chopped down or tilled in, roots and tops decompose into stable humus
• Fix nitrogen (legume cover crops) — clover, vetch, peas, fava beans add 50–200 lb N/acre via symbiosis with rhizobia bacteria
• Break compaction — deep-rooted crops (daikon radish, sunflower, sorghum-sudangrass) drill through compacted layers
• Suppress weeds — dense cover crowds out weed seedlings; some species (rye, buckwheat) are mildly allelopathic
• Feed soil biology — root exudates support the [[soil-food-web|soil food web]] continuously
• Host beneficials — flowering cover crops (buckwheat, phacelia, crimson clover) support pollinators and predatory insects
• Scavenge nutrients — deep-rooted crops pull leached nutrients back from below the root zone of vegetables

Common cover crops by season

Fall-planted (overwintering or winter-killed):

• Winter rye — extremely cold-hardy, deep roots, large biomass, mild allelopathy. The workhorse.
• Hairy vetch — legume; fixes substantial N; overwinters in most zones; pairs well with rye
• Crimson clover — legume; overwinters in milder zones; spectacular spring bloom for pollinators
• Oats and field peas — winter-kills in cold zones; leaves residue without spring termination required
• Tillage radish / daikon — winter-kills; deep root opens compaction; “biological tillage”

Spring or summer-planted (short-cycle):

• Buckwheat — 30–45 days to bloom; smothers weeds; great pollinator plant; winter-kills
• Sudangrass / sorghum-sudangrass — massive biomass in heat
• Cowpea (Southern pea) — legume; heat-tolerant; nitrogen fixation in summer slots
• Sun hemp — tropical legume; rapid summer growth

Termination

Cover crops must be killed before they go to seed, or they become weeds. Termination methods:

• Mowing or scything — followed by [[silage-tarp|silage tarp]] (occultation) to fully kill regrowth
• Crimping or roller-crimping — rolling a crop flat at flowering kills most cover crops without tillage; specialized but extremely effective
• Tilling in — traditional method; effective but undoes much of the soil benefit
• Tarping — the no-till market-garden standard now
• Winter-killing — some species (oats, buckwheat, field peas) die at first hard freeze; ideal for fall planting in cold climates

In a home garden

Even a small home garden benefits from cover-cropping the beds not in production. The simplest practice:

• After fall harvest: scatter winter rye or oats + crimson clover; rake in; water once if soil is dry; leave alone for the winter
• Spring: 4–6 weeks before planting the bed, mow or chop, tarp for 3 weeks, plant

The bed coming out the other side of this is dramatically better than the bed left bare or covered only with leaves.

See also

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• Subset of: [[gardening]]
• Shares approach with: [[green-manure]] · [[crop-rotation]]
• Member of: [[practice]]

Sources

• Managing Cover Crops Profitably (SARE, 3rd ed. 2007) — the comprehensive reference; freely available
• Eliot Coleman, The New Organic Grower — cover-cropping in market-garden rotations
• Northeast Cover Crops Council technical guidance

Rooted in life.