How to Grow Cover Crops (Legumes)

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Cover Crops (Legumes)

Fabaceae family (various genera including Trifolium, Medicago, Vicia, Lupinus)

grass

Legume cover crops are nitrogen-fixing plants grown primarily to improve soil health rather than for harvest. They include clovers, alfalfa, vetches, and lupines that form symbiotic relationships with soil bacteria to convert atmospheric nitrogen into plant-available forms. These crops are tilled back into soil to increase organic matter and fertility for subsequent plantings.

Looking for a specific variety?

Red Clover White Clover Alfalfa Hairy Vetch Crimson Clover Field Peas

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Example Cover Crops (Legumes) timeline · Pittsburgh, PA (Zone 6b)

Plant Cover Crops (Legumes)
Around Apr 17

Near Pittsburgh's average last spring frost.
Tend & protect
Late spring–summer

Watering, feeding, and pest-watch reminders.
Harvest Cover Crops (Legumes)
Around Jun 16

≈ 60 days after planting

Sample dates for Pittsburgh, PA. Sign up to get exact Cover Crops (Legumes) dates for your own zip code.

Growing Conditions

☀️

Sun: Full sun, 6-8 hours daily; some species tolerate partial shade

💧

Water: Moderate moisture; most legumes prefer 1-1.5 inches per week once established; drought-tolerant after establishment; avoid waterlogging

📏

Spacing: Varies by species; typically broadcast at 15-20 lbs/acre for clover, 8-12 lbs/acre for alfalfa; row spacing 6-12 inches if drilled inches

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Days to maturity: 60-120 days to full ground cover; nitrogen fixation begins 3-4 weeks after germination

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Planting depth: 0.25-0.5 inches; small seeds should be lightly pressed into soil

Soil

Type: Well-draining loamy to sandy soil; tolerant of poor soils

pH: 6.0-7.5

Amendments:

Inoculant with appropriate Rhizobium bacteria (critical for nitrogen fixation) Phosphorus if deficient Potassium if deficient Lime in acidic soils below pH 6.0

Growing Zones

Find your zone →

Varies by species; cool-season legumes thrive in zones 2-7, warm-season varieties in zones 6-10

2a 2b 3a 3b 4a 4b 5a 5b 6a 6b 7a 7b 8a 8b 9a 9b 10a

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Growth Stages

Germination & Seedling

7-14 days germination; nodulation begins week 2-3

Tiny legume seedlings emerge with characteristic heart-shaped cotyledons; root nodulation begins as Rhizobium bacteria colonize roots

Ensure adequate soil moisture for germination; apply inoculant before planting for reliable nodulation; avoid crusting soils that prevent emergence

Vegetative Growth

4-8 weeks depending on species and season

Rapid leaf and stem development; trifoliate or pinnate leaves appear; plant spreads laterally through stolons (clovers) or erect stems (vetches, alfalfa); nodules visible on roots by week 4

Maintain consistent moisture; avoid nitrogen fertilizer which inhibits nodulation; light grazing or mowing may encourage branching

Ground Cover & Nitrogen Fixation

4-12 weeks (extends through season for perennial legumes)

Plant achieves desired ground cover density; active nitrogen fixation occurring in root nodules; plant canopy smothers weeds and improves soil structure

Monitor for pests and diseases; most cover crops need no inputs at this stage; ensure adequate soil moisture if dry

Flowering

2-4 weeks before termination

Flower buds and blooms appear (optional stage; often happens before incorporation); flowers attract beneficial pollinators

Allow flowering to maximize biomass and root nodule development before termination; provides nectar for beneficial insects

Incorporation & Decomposition

2-4 weeks soil incorporation; active decomposition 4-8 weeks

Cover crop is tilled, chopped, or allowed to winter-kill; above-ground biomass decomposes; nitrogen and organic matter integrate into soil

Till 4-6 inches deep for maximum incorporation; wait 2-4 weeks before planting cash crop to allow decomposition; incorporate in late fall or early spring before flowering for optimal nitrogen release

Companion Planting

Plan your garden →

Plant with:

Cereal grains (oats, rye, barley) in mixed cover crop blends Brassicas in crop rotation Root vegetables in subsequent plantings Fruit trees and berries benefit from soil improvement

Avoid planting near:

Other legume cover crops in same field (potential disease buildup) Nitrogen-hungry crops without adequate mineralization time Areas treated with recent herbicides that inhibit legume growth

Common Pests

Rotate crops annually; most cover crops are resistant; larvae rarely cause economic damage in cover crops
Generally not problematic in cover crops; if widespread, encourage beneficial insects or use reflective mulch
Harvest or incorporate cover crop before significant defoliation; rotate fields annually
and
Manage excessive moisture and shade; encourage predatory insects; rarely economically significant for cover crops
Adequate air circulation; moisture management; most cover crops tolerate mild infection

Uses

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Edible sprouts and microgreens

Culinary

Some legume cover crops like alfalfa and clover can be harvested as sprouts or microgreens for salads and garnishes, offering high nutritional density and fresh flavor. [source]

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Nitrogen fixation and soil fertility

Household

Legume-Rhizobium symbiosis converts atmospheric nitrogen into bioavailable nitrate, adding 100-200+ lbs nitrogen per acre naturally without synthetic fertilizer, significantly improving soil fertility for subsequent crops. [source]

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Organic matter and soil structure improvement

Household

Cover crop biomass decomposes to increase humus content, improving soil aggregation, water retention, aeration, and microbial community; long-term use builds resilient, fertile soils. [source]

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Pollinator and beneficial insect habitat

Wildlife

Flowering legume cover crops provide nectar and pollen for bees, butterflies, and beneficial parasitoid wasps that control crop pests, supporting ecosystem health in agricultural systems. [source]

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Weed and pest suppression

Household

Dense cover crop growth shades and suppresses weeds; allelopathic compounds in some species inhibit weed germination; breaks pest cycles through crop rotation and living mulch effects. [source]

Harvest Tips

Cover crops are not harvested for yield but rather incorporated into soil. Best timing: 4-8 weeks before planting cash crop in spring, or in late fall for winter termination. For maximum nitrogen contribution, incorporate at early flower/late vegetative stage. Winter-kill covers in cold zones; warm-season covers can be terminated by frost or tillage. Allow 2-4 weeks soil integration before planting nitrogen-hungry crops.

Fun Facts

🌱 A single acre of legume cover crop can fix 100-300 pounds of nitrogen from the atmosphere—equivalent to applying 200-600+ pounds of synthetic nitrogen fertilizer, making cover crops a cornerstone of sustainable agriculture.
🌱 The nitrogen-fixing relationship between legumes and Rhizobium bacteria is so efficient that some farmers have reduced or eliminated synthetic nitrogen inputs entirely through intelligent cover crop rotations, cutting input costs and environmental impact.
🌱 Cover crops aren't new—Roman farmers used them 2,000 years ago, rotating legumes with grains in a practice called 'green manuring,' making this one of agriculture's oldest and most time-tested techniques.

Gardening Terms

New to gardening? Learn about terms used in this guide:

Cover Crop Full Sun Germination Partial Shade pH

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