Ornamental · Fabaceae

Alfalfa

Medicago sativa

Get the soil and pH right before you seed, and this deep-rooted legume keeps cutting for years.

Light

Full sun

Water

Every 7–⁠14 days

Harvest

60–⁠70 days

Hardiness

USDA 3–⁠9

Pet-safe
Alfalfa

Overview

Alfalfa is the workhorse of the forage world, a deep-rooted perennial legume that growers cut several times a season for hay. It belongs to the pea family, and like its relatives it pulls its own nitrogen from the air through Rhizobium bacteria living in its root nodules. That taproot drives down a long way, which is why a well-set stand shrugs off drought and keeps coming back year after year.

Where alfalfa gets particular is the ground it sits in. It wants deep, well-drained, near-neutral soil and turns sulky on acidic, soggy, or shallow sites. Get the pH and drainage right before you seed and the crop rewards you for years; get them wrong and the stand thins out fast. In summer it throws up purple to blue-violet pea flowers, though most growers cut for forage well before bloom takes over.

It is also a plant with a long memory of itself. An old stand poisons the ground against its own seedlings, an effect called autotoxicity, so you can't just reseed straight back into a tired field. Work alfalfa into a rotation instead, and the next crop gets the bonus of the nitrogen it left behind.

Care

The short version: full sun and deep, well-drained, near-neutral soil at a pH of 6.5 to 7.5. Inoculate the seed, water deeply but seldom once it's rooted, and cut on a regular schedule through the season.

Light

Alfalfa is a full-sun crop with no real tolerance for shade. Open ground with all-day sun is what drives the heavy regrowth between cuttings.

Water

Once it's established the deep taproot makes alfalfa very drought tolerant, so water deeply and only every 7 to 14 days rather than little and often. It needs roughly 10 to 12 inches of moisture over a season but cannot stand flooding or waterlogged ground, so drainage matters as much as the water itself.

Soil

Give it deep, well-drained, fertile loam and keep the pH between 6.5 and 7.5. It does poorly on acidic, very alkaline, wet, or shallow soils, and that fussiness about the seedbed is the single biggest factor in whether a stand succeeds.

Temperature

Alfalfa is tough at both ends, handling a range from about -20°F to 95°F (-29°C to 35°C) across its hardiness zones. That cold tolerance is what lets winter-hardy types survive northern winters and come back each spring.

Humidity

Ordinary outdoor humidity is no concern for a field crop like this. What matters far more is air movement and drainage, since damp, stagnant conditions are what invite the root rots and white mold.

Feeding

As a legume, alfalfa fixes its own nitrogen through Rhizobium nodules once the seed is inoculated, so you don't feed it nitrogen. Instead supply phosphorus, potassium, and lime by soil test to hold the pH near neutral, both at establishment and after cuttings.

Pruning

Cutting is the whole point of the crop. Take the first harvest from a direct-seeded stand about 60 days after seeding, then cut on a regular schedule through the season for hay or forage.

Repotting

none

Size & spacing

A mature stand stands about 24 to 35 inches (60 to 90 cm) tall with plants spreading 12 to 24 inches (30 to 60 cm) across. Because it's broadcast or drilled as a field crop rather than spaced like a garden plant, you manage it as a dense stand rather than individual plants.

When to plant

Alfalfa goes in by direct seeding, not from transplants. Sow into a firm seedbed in spring or again in late summer, take a first cut about 60 days later, and keep cutting through the warm months as the purple flowers come and go.

Northern hemisphere

Sow Apr–May
Sow Jul–Sep
Bloom May–Oct
Harvest Jun–Oct

Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.

  • Sow: Not typical; direct sown in field
  • Plant: Spring (April-May) or late summer (late July-early September) into a firm, well-drained seedbed at neutral pH
  • Harvest: Purple to blue-violet pea flowers in summer (May-October depending on latitude); cut for hay or forage multiple times per season

Hardiness

USDA hardiness zones: 3–9

Temperature: down to -40°C

Troubleshooting

Most alfalfa trouble starts underground or in the seedbed, where bad soil and old-stand chemistry do their damage before you ever see it. The rest shows up on the leaves as pests move in. Match what you're seeing below and act while the stand can still recover.

Severe

Stand thins out or never takes hold

Alfalfa is fussy about its ground, and a failing stand usually means the soil is too acidic or too wet. In acid soil the Rhizobia that feed the plant go dormant, and standing water rots the roots and heaves crowns over winter. Lime the ground to near neutral well before seeding, pick a deep, well-drained field, and inoculate the seed so the roots nodulate properly.

Fix:

  • Lime acidic soils to pH 6.5-7.0 at least six months before seeding if pH is below 6.2
  • Select deep, well-drained fields and avoid hilltops, eroded ground, and low spots where water pools
  • Inoculate seed with the correct Rhizobium and ensure good seed-to-soil contact in a firm seedbed
Severe

New seeding into an old alfalfa field comes up thin and stunted

This is autotoxicity, and it catches a lot of growers out. An established alfalfa stand releases compounds that block its own seedlings from germinating and growing, so a fresh seeding right back into the old field comes up sparse and far below the 25 plants per square foot you need. Rotate to corn or a grass for at least a year before you put alfalfa back, and let the rotation crop use up the residual nitrogen.

Fix:

  • Do not reseed alfalfa directly back into an old alfalfa stand
  • Rotate to a non-alfalfa crop such as corn or a grass for at least one year before returning to alfalfa
  • Use the residual nitrogen from the old stand for the rotation crop
Severe

Wilting, yellow-green plants and rotting crowns

Several diseases show up as a slow stand decline, and wet ground brings on the worst of them. Phytophthora and Aphanomyces root rots brown out the roots in soggy fields, bacterial wilt leaves plants stunted and yellow-green, and Sclerotinia coats the crowns in white cottony mold. Plant resistant cultivars, fix the drainage, and rotate away from alfalfa to knock back the inoculum in the soil.

Fix:

  • Plant disease-resistant cultivars (bacterial wilt, Phytophthora, Aphanomyces resistant)
  • Improve drainage and avoid wet, low fields
  • Rotate away from alfalfa to reduce soilborne inoculum
Setback

Chewed or yellowed leaves and a thinning crop

Three pests do most of this damage. Alfalfa weevil larvae chew and skeletonize the new growth, potato leafhopper turns the leaf edges yellow with a burn the books call hopperburn, and aphids pile on top. Sweep-net the field to see what you actually have, treat once counts cross the economic threshold, and cut early or plant leafhopper-resistant cultivars to stay ahead of them.

Fix:

  • Scout regularly and treat at established economic thresholds
  • Use early or timely cutting to disrupt pest cycles
  • Plant potato-leafhopper-resistant and pest-resistant cultivars where available

Toxicity

Alfalfa is safe across the board and never appears on the ASPCA toxic-plant lists. People eat it as sprouts and supplements, and it feeds cats, dogs, rabbits, horses, and poultry without harm. The one thing to watch is grazing cattle and sheep, where a lush stand can bring on bloat, so manage the pasture rather than fear the plant.

Safe for

People · Cats · Dogs · Horses · Rabbits · Livestock · Birds

Cats None

Alfalfa is not toxic to cats, and it never appears on the ASPCA poison lists. A curious nibble does nothing more than the odd grass would.

Dogs None

Dogs can be around alfalfa with no worry. Dried alfalfa even turns up as an ingredient in some pet foods, so there is nothing here to keep them away from.

Horses Safe

Horses eat alfalfa as a rich hay and handle it well. It is one of the more nutritious forages you can feed them.

Rabbits Safe

Alfalfa is a staple in many rabbit diets and a favorite treat. Young rabbits in particular do well on it.

Livestock Mild

Cattle and sheep graze alfalfa safely, with one real catch worth knowing. A lush, pure stand can bring on frothy bloat that swells the left flank, and fresh growth rarely triggers photosensitization. Keep the legume to about a third of the pasture, feed hay before turnout, and don't push hungry animals onto a heavy stand.

Birds Safe

Birds can eat alfalfa without harm, and poultry take it readily as a green feed.

People Safe

People eat alfalfa too, most often as sprouts or as a dried supplement. The plant carries no toxins that make it unsafe.

Not poisonous to cats, dogs, or people. The only real caveats are with grazing ruminant livestock: lush alfalfa can cause frothy bloat in cattle and sheep grazed heavily, fresh alfalfa can rarely cause photosensitization, and alfalfa contains phytoestrogens. Limit legume to about 30 percent or less of pasture, feed hay before turnout, and avoid turning hungry animals onto lush stands.

Varieties

Alfalfa varieties sort out mainly by how dormant they go in fall and what diseases they resist. These are the distinctions worth knowing before you buy seed.

Fall-dormant (winter-hardy northern) types, FD 2-4

Their low fall-dormancy rating makes them slow down early and survive hard winters, which is what you want in cold northern ground.

Non-dormant (southern) types, FD 8-9

A high fall-dormancy rating keeps these plants growing late into the season for warm southern regions, at the cost of winter hardiness.

'Alfagraze'

Bred to take the beating of grazing, this cultivar became the benchmark that grazing-tolerance trials measure others against.

Disease-resistant modern cultivars

These newer lines stack resistance to bacterial wilt, Phytophthora and Aphanomyces root rots, Fusarium wilt, anthracnose, and the potato leafhopper.

Companions

Plant near

Grasses (orchardgrass, timothy)Corn or other rotation crops following alfalfa

Grasses (orchardgrass, timothy): Grass-alfalfa mixtures reduce frothy bloat risk in grazing ruminants and improve stand productivity.

Corn or other rotation crops following alfalfa: Rotating to a non-alfalfa crop for a year uses alfalfa's residual nitrogen and avoids autotoxicity when returning to alfalfa.

Keep apart

New alfalfa seeded into an existing alfalfa stand

New alfalfa seeded into an existing alfalfa stand: Autotoxicity from the established alfalfa inhibits germination and growth of the new alfalfa seedlings.

How to propagate

Alfalfa is grown from seed sown straight into the field, and the trick is less about the sowing than about getting the seedbed, the inoculant, and the rotation right.

SeedModerate

Spring (April-May) or late summer (late July-early September) · About 60 days to first harvest; full stand establishes over the seeding year

Alfalfa is direct sown, not started indoors, either in spring around April to May or in late summer from late July into early September. Inoculate the seed with the right Rhizobium so it can fix its own nitrogen, then sow it a quarter to half an inch deep, a little deeper in sandy ground, into a firm, well-drained, near-neutral seedbed. You can take a first cut about 60 days in, but the full stand fills out over the rest of the seeding year. One firm rule holds it all together: never seed alfalfa straight back into an old alfalfa field, or autotoxicity will wreck the new stand.

Myths

Myth

Alfalfa is poisonous and unsafe to feed to animals or people.

Reality

Alfalfa is a safe, nutritious forage fed to livestock and rabbits, taken as a supplement by people, and used in some pet diets, and it never appears on ASPCA toxic-plant lists. The one genuine caveat is frothy bloat in cattle and sheep turned onto a lush stand, along with rare photosensitization and some phytoestrogen content. None of that makes the plant poisonous to pets or people.

Sources