Alfalfa as a Cover Crop
Legume cover crop
Alfalfa (Medicago sativa) is a deep-rooted perennial legume long valued on farms and increasingly used by gardeners as a soil-building cover crop. Left in place for a full season or longer, it can serve as a living mulch, a rotation break, or a source of homegrown organic matter. Because it is a perennial, it fits situations where a bed or field section can rest for a year or more rather than a quick fall-to-spring window.
Benefits
As a legume, alfalfa works with soil bacteria to draw nitrogen from the air and hold it in the plant and root system, which can add nitrogen to the soil as the residue breaks down. Its taproot can reach deep into the profile, helping to open compacted layers and improve water movement and soil structure over time. Frequent regrowth produces a steady supply of top growth and root turnover that builds organic matter, while its dense stand and canopy help shade out weeds and protect the surface from erosion. These effects generally develop over a full growing season rather than in a few weeks.
When to plant
Alfalfa is most often seeded in spring after the soil has warmed and settled, or in late summer where the region allows enough growth before cold weather arrives. It needs firm contact between the small seed and the soil, so a well-prepared, firmed seedbed and shallow placement work best. Seeding is usually done at a light to moderate rate for cover-crop stands; your local Cooperative Extension can suggest a range and timing suited to your area and soil.
Growing it
Alfalfa establishes slowly at first, then forms an upright, branching stand that regrows after cutting and returns for several years under the right conditions. It prefers well-drained soil and a near-neutral pH, and it tends to struggle in wet, poorly drained, or strongly acidic ground, so a soil test ahead of planting is a good idea. Periodic mowing during the season keeps growth manageable, encourages regrowth, and helps suppress weeds.
Ending the cover crop
Because alfalfa is a persistent perennial, ending the stand by mechanical means usually takes more effort than annual cover crops. Repeated close mowing followed by tilling or turning the crowns and roots into the soil is a common non-chemical approach, and cutting when plants are in bud or bloom while root reserves are lower can make removal easier. Give the incorporated residue a few weeks to break down before planting a following crop, and check with your Cooperative Extension for methods matched to your equipment and soil.
Best for
Alfalfa suits gardeners and small farmers who can dedicate a bed or field section to a longer soil-building rest of a full season or more, especially on well-drained, near-neutral soils. It is a good fit when the goal is deep rooting, added organic matter, and nitrogen contribution rather than a quick cover between two cash crops.
General guidance for US growers. Seeding rates and regional mixes vary; your local Cooperative Extension office and NRCS can help you plan. Page updated Aug 4, 2026.