Ornamental · Fabaceae

Alfalfa

Medicago sativa

Correct the soil pH and drainage first, because everything from nodulation to winter survival in this taprooted legume follows from it.

Light

Full sun

Water

Every 7–⁠14 days

Harvest

60–⁠70 days

Hardiness

USDA 3–⁠9

Pet-safe
Alfalfa

Overview

Alfalfa is the mainstay forage legume, a deep-taprooted perennial in the pea family that growers cut several times each season for hay. Like other legumes, it acquires its own nitrogen from the atmosphere through Rhizobium bacteria housed in its root nodules, which is why an inoculated stand needs no nitrogen feeding. The taproot itself reaches deep into the profile, and that single trait explains the crop's strong drought tolerance and its habit of returning year after year.

The ground is where alfalfa proves selective. It demands deep, well-drained, near-neutral soil and performs badly on acidic, waterlogged, or shallow sites, for a clear reason: acid conditions suppress the Rhizobia so nodulation fails, and shallow soil cuts off the taproot depth the plant relies on. Set the pH and drainage correctly before seeding and the stand pays back for years. In summer it raises purple to blue-violet pea flowers, though most fields are cut for forage ahead of full bloom.

It is also a crop with a chemical memory of itself. A mature stand releases allelopathic compounds that turn the ground against its own seedlings, the effect known as autotoxicity, so reseeding straight into a tired field is a losing move. Fold alfalfa into a rotation instead, and the following crop draws on the residual nitrogen left in the soil.

Care

The short version: plant in full sun on deep, well-drained, near-neutral ground at a pH of 6.5 to 7.5. Inoculate the seed so nodules form, water deeply but seldom once the taproot is down, and cut on a steady schedule across the season.

Light

Treat alfalfa as a full-sun crop with no shade tolerance to speak of. Open ground under all-day sun supplies the photosynthetic capacity that powers the heavy regrowth a stand must put on between successive cuttings.

Water

An established taproot makes this legume very drought tolerant, so the right approach is deep watering every 7 to 14 days, letting the top half dry, rather than frequent shallow doses. A season calls for roughly 10 to 12 inches of moisture, yet the roots need oxygen and will not survive flooding or waterlogging, which is why well-drained ground counts as much as the water you apply.

Soil

Aim for deep, well-drained, fertile loam held between a pH of 6.5 and 7.5. It struggles on acidic, very alkaline, wet, or shallow soils, and since acid ground sidelines the Rhizobia and shallow ground caps taproot depth, the quality of that seedbed is the strongest single predictor of whether a stand takes.

Temperature

The crop endures a wide swing, from about -20°F to 95°F (-29°C to 35°C) across its hardiness range. That cold hardiness is what allows fall-dormant types to come through northern winters and break dormancy again each spring.

Humidity

Open-air humidity is no issue for a field crop of this kind. Air movement and drainage carry far more weight, because damp, stagnant conditions are precisely what tip the balance toward root rots and white mold.

Feeding

As a legume, alfalfa draws its own nitrogen out of the air through Rhizobium nodules the moment the seed is inoculated, which makes any nitrogen application pointless. What it does want is phosphorus, potassium, and lime guided by a soil test to keep pH near neutral, given at establishment and again after cuttings.

Pruning

Harvesting by cutting is the whole reason to grow it. Take that opening cut from a direct-seeded stand roughly 60 days after seeding, and from there return on a steady interval through the season to bank hay or forage.

Repotting

none

Size & spacing

At maturity the canopy reaches roughly 24 to 35 inches (60 to 90 cm) in height, with individual plants spreading 12 to 24 inches (30 to 60 cm). Since it is broadcast or drilled as a field crop rather than set out as spaced individuals, you manage the result as a dense stand.

When to plant

This is a direct-seeded field crop rather than a transplant. Drill it into a firm seedbed in spring or come back in late summer, lift a first cut roughly 60 days on, and continue cutting through the warm months while the purple flowering runs its course.

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

The hardest alfalfa problems begin out of sight, in the chemistry of the seedbed and the residue of a previous stand, and they have usually done their work before any symptom reaches the canopy. Leaf damage from insects arrives later. Read what the stand is telling you below and intervene while recovery is still possible.

Severe

A stand that establishes poorly or declines to a thin cover

A failing stand almost always traces back to ground on the acid side or ground that holds water. The cause-and-effect is plain: where acidity prevails the Rhizobia go dormant, nodulation never gets going, and pooled water suffocates roots, rots them, and shoves crowns up out of the soil through winter. The remedy is to lime toward neutral well in advance, pick a site with depth and free drainage, and treat the seed with inoculant so the roots colonize and nodulate.

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

Reseeded ground yields sparse, undersized seedlings

This is autotoxicity at work. An established stand puts out allelopathic compounds that block germination and growth of fresh alfalfa seedlings, so a reseed straight into the old field emerges sparse, well under the 25 plants per square foot a productive stand requires. Skip reseeding alfalfa into alfalfa and rotate to corn or a grass for at least one year first, which also lets the rotation crop draw down 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, chlorotic plants with decaying crowns

Disease usually reads as a slow thinning of the stand, and saturated ground draws out its sharpest forms. Phytophthora and Aphanomyces root rots break down roots in waterlogged soil, bacterial wilt holds plants stunted and yellow-green, and Sclerotinia wraps the crowns in white cottony mycelium. Choose resistant cultivars, fix the drainage so soil drains and stays aerated, and rotate off alfalfa to draw down the soilborne inoculum.

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

Foliage showing feeding damage and yellowing as the crop thins

Three insects account for most of this. Alfalfa weevil larvae chew and skeletonize the developing leaves, potato leafhopper feeding yellows the leaf margins in the burn known as hopperburn and stunts the plant, and aphids add to the load. Sweep-net to confirm what is present, treat once counts reach economic thresholds, and use early, timely cutting plus leafhopper-resistant cultivars to break the pest cycle.

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 carries no toxins of concern and stays off the ASPCA poison lists entirely. People consume it as sprouts and supplements, and cats, dogs, rabbits, horses, and poultry all handle it. The single management point sits with grazing cattle and sheep, where a lush pure stand can provoke bloat, so the answer is pasture management rather than avoiding the plant.

Safe for

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

Cats None

Alfalfa poses no toxicity to cats and has never been listed by the ASPCA. A passing nibble amounts to no more than chewing ordinary grass would.

Dogs None

Dogs are fine around alfalfa. Dried alfalfa even shows up as an ingredient in certain pet foods, so there is nothing here to fence them away from.

Horses Safe

Horses take alfalfa as a rich, nutritious hay and tolerate it well, ranking it among the better forages on offer.

Rabbits Safe

Alfalfa is a staple in many rabbit diets and a clear favorite, with young rabbits in particular thriving on it.

Livestock Mild

Grazing it poses no problem for cattle and sheep, save for one issue worth respecting: a lush, pure stand may bring on frothy bloat that swells the left flank, and new growth rarely sets off photosensitization. Cap the legume near a third of the pasture, offer hay ahead of turnout, and keep hungry stock off a heavy stand.

Birds Safe

Birds come to no harm from alfalfa, and poultry readily take it as a green feed.

People Safe

People eat alfalfa as well, most often as sprouts or a dried supplement, since the plant carries nothing that would 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

What separates one alfalfa from another comes down chiefly to fall-dormancy behavior and the disease package it carries. Here are the distinctions to settle before committing to a seed lot.

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

A low fall-dormancy rating triggers earlier dormancy and hardens these northern types against severe winters, which is exactly what cold ground demands of a winter-hardy line.

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

A high fall-dormancy rating sustains late-season growth suited to warm southern regions, with winter hardiness given up as the trade in these non-dormant types.

'Alfagraze'

'Alfagraze' was bred for grazing tolerance and went on to become the benchmark against which grazing-tolerance trials measure other lines.

Disease-resistant modern cultivars

Modern disease-resistant lines combine protection against several threats at once: bacterial wilt, the Phytophthora and Aphanomyces root rots, Fusarium wilt, anthracnose, and feeding by 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 establishes from seed placed straight into the field, and success hinges far less on the act of sowing than on the seedbed firmness, the inoculant, and the cropping sequence that came before it.

SeedModerate

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

Sow this crop straight into open ground, never indoors. Two windows work: spring, April to May, or the late-summer slot running late July into early September. Start by coating seed with the correct Rhizobium so nitrogen fixation can begin, then drill it a quarter to half an inch deep, dropping it slightly farther in sandy ground, onto a firm bed that drains freely and sits near neutral. A first cut follows about 60 days later, and the stand keeps thickening through the balance of that first year. One rule is absolute: do not put alfalfa back into a spent alfalfa field, since autotoxicity will ruin whatever germinates.

Myths

Myth

It is often claimed that alfalfa is poisonous and unsafe as feed for livestock or people.

Reality

In practice it is a safe, nutritious forage: livestock and rabbits eat it, people take it as a supplement, some pet diets include it, and the ASPCA has never flagged it as toxic. The one true exception involves cattle and sheep moved onto a lush stand, which can develop frothy bloat, alongside occasional photosensitization and a degree of phytoestrogen content. Not one of those points makes the plant poisonous to a pet or a person.

Sources