Ornamental · Fabaceae

Alfalfa

Medicago sativa

Settle the soil and pH before a single seed goes down, and this deep-rooted legume rewards you with cutting after 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 quiet heavyweight of forage, a deep-rooted perennial legume that growers lift several times a year for hay. It sits within the pea family, and in the manner of its kin it draws nitrogen out of the air through Rhizobium bacteria settled in nodules along its roots. The taproot plunges far below the surface, which is why a well-founded stand brushes off dry spells and returns season after season.

Where alfalfa shows its temperament is the ground beneath it. The crop asks for deep, well-drained, near-neutral soil and sulks on acidic, sodden, or thin sites. Settle the pH and drainage before seeding and it pays you back for years; miss them and the stand grows sparse in short order. Across summer it lifts purple to blue-violet pea flowers over the rolling green, a soft wash of color most growers cut for forage before bloom takes hold.

It is also a crop with a long recollection of itself. A tired stand turns the earth against its own seedlings, a quirk known as autotoxicity, so dropping fresh seed straight back into a worn field will not do. Fold alfalfa into a rotation instead, and the crop that follows inherits the nitrogen it left in the soil.

Care

The short version: open sun and a deep, well-drained, near-neutral bed at a pH of 6.5 to 7.5. Coat the seed with inoculant, water with depth rather than frequency once the roots find their footing, and keep to a steady cutting rhythm all season.

Light

Alfalfa is a creature of full sun with no patience for shade. Open ground bathed in light from morning to dusk is what powers the heavy flush of regrowth between each cutting.

Water

Once settled, the deep taproot leaves alfalfa very drought tolerant, so the wiser approach is to water deeply and only every 7 to 14 days, never in small frequent sips. The crop wants somewhere near 10 to 12 inches of moisture across a season, yet it will not abide flooding or waterlogged ground, which makes drainage count for as much as the watering can.

Soil

Offer it deep, well-drained, fertile loam and hold the pH between 6.5 and 7.5. The crop fares badly on acidic, very alkaline, wet, or shallow soils, and that exacting taste in a seedbed is the one factor that most decides whether a stand thrives.

Temperature

Alfalfa holds its own at both extremes, weathering a span from about -20°F to 95°F (-29°C to 35°C) across its hardiness zones. That hardiness in the cold is what carries winter-tough types through northern winters to green up again each spring.

Humidity

Everyday outdoor humidity is of no concern to a field crop of this sort. Far more telling is air movement and drainage, since damp, still conditions are precisely what summon the root rots and white mold.

Feeding

As a legume, alfalfa draws its own nitrogen through Rhizobium nodules once the seed has been inoculated, so nitrogen feeding is off the table. What it does ask for is phosphorus, potassium, and lime guided by a soil test to keep the pH near neutral, both at the start and after each round of cuttings.

Pruning

Cutting is the entire purpose here. Lift the first harvest from a direct-seeded stand around 60 days after seeding, then settle into a steady cutting schedule across the season for hay or forage.

Repotting

none

Size & spacing

A grown stand reaches about 24 to 35 inches (60 to 90 cm) tall, with plants reaching 12 to 24 inches (30 to 60 cm) across. Since it is broadcast or drilled as a field crop rather than set out like a border specimen, you tend it as one dense sweep rather than as separate plants.

When to plant

Alfalfa arrives by direct seeding rather than from a tray of transplants. Lay it into a firm bed in spring or come back to it in late summer, lift a first cut roughly 60 days on, and carry the rhythm through the warm months while those purple blossoms drift in and out of the stand.

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 of what goes wrong with alfalfa begins out of sight, in the bed or the chemistry the old crop left behind, long before a single symptom reaches the surface. The remainder writes itself across the leaves as insects arrive. Read the field against what follows and step in while the stand still has the strength to recover.

Severe

A stand that comes in uneven or never quite takes

Alfalfa is choosy about its footing, and a failing stand nearly always traces back to soil that runs too acidic or too wet. In sour ground the Rhizobia that feed the plant fall dormant, while standing water rots the roots and lifts crowns out over winter. Bring the ground to near neutral well ahead of seeding, choose a deep, well-drained field, and inoculate the seed so the roots take on proper nodulation.

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

Old ground reseeded, only to rise sparse and stunted

This is autotoxicity, and it blindsides plenty of growers. A settled alfalfa stand gives off compounds that bar its own seedlings from germinating and growing, so fresh seed dropped straight back into the old field rises sparse and well under the 25 plants per square foot the field needs. Turn to corn or a grass for a year at least before alfalfa returns, and let that interim crop spend the nitrogen the old stand left behind.

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

Plants slumping pale, their crowns softening to rot

A handful of diseases surface as a gradual fade of the stand, and wet ground draws out the worst. Phytophthora and Aphanomyces root rots brown the roots in soggy fields, bacterial wilt leaves plants stunted and yellow-green, and Sclerotinia wraps the crowns in a white cottony mold. Set in resistant cultivars, sharpen the drainage, and rotate clear of alfalfa to thin the inoculum waiting 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

Foliage marked by feeding and yellowing as the crop thins

Three insects carry out most of this mischief. Alfalfa weevil larvae chew and skeletonize the tender new growth, potato leafhopper scorches the leaf margins yellow in what is called hopperburn and stunts the plant, and aphids round out the cast. Run a sweep net to learn what is truly present, treat once counts pass the economic threshold, and cut early or set in leafhopper-resistant cultivars to keep 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 right down the line and has never earned a place on the ASPCA toxic-plant lists. People take it as sprouts and supplements, and it nourishes cats, dogs, rabbits, horses, and poultry without trouble. The single qualifier sits with grazing cattle and sheep, where a heavy stand can tip into bloat, so the answer is to manage the pasture rather than mistrust the plant.

Safe for

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

Cats None

Alfalfa poses no toxic threat to cats and has never surfaced on the ASPCA poison lists. A curious nibble amounts to no more than a mouthful of ordinary grass would.

Dogs None

Dogs can keep company with alfalfa without any concern. Dried alfalfa even features as an ingredient in some pet foods, so there is nothing here worth steering them away from.

Horses Safe

Horses take alfalfa as a rich hay and do well on it. It ranks among the more nourishing forages you can set in front of them.

Rabbits Safe

Alfalfa is a mainstay of many rabbit diets and a treat they favor. Young rabbits in particular flourish on it.

Livestock Mild

Cattle and sheep graze alfalfa safely, with a single real caveat worth carrying. A heavy, pure stand can bring on frothy bloat that distends the left flank, and fresh growth on rare occasions sets off photosensitization. Hold the legume to roughly a third of the pasture, feed hay ahead of turnout, and resist driving hungry animals onto a heavy stand.

Birds Safe

Birds take alfalfa with no ill effect, and poultry accept it freely as a green feed.

People Safe

People enjoy alfalfa as well, most commonly as sprouts or as a dried supplement. The plant holds no toxins 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

The choices in alfalfa come down chiefly to how far each type winds down in fall and which diseases it shrugs off. Here are the distinctions worth weighing before the seed order goes in.

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

A low fall-dormancy rating has these types ease off early and ride out hard winters, which is exactly the trait you reach for in cold northern ground.

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

A high fall-dormancy rating keeps these plants pressing on late into the season for warm southern regions, traded against a measure of winter hardiness.

'Alfagraze'

Shaped to withstand the wear of grazing, 'Alfagraze' grew into the benchmark that grazing-tolerance trials hold others up against.

Disease-resistant modern cultivars

The modern lines layer protection against bacterial wilt, Phytophthora and Aphanomyces root rots, Fusarium wilt, anthracnose, and the leaf-yellowing 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 raised from seed laid straight into open ground, and the craft lies less in the act of sowing than in getting the bed, the inoculant, and the rotation in good order.

SeedModerate

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

This crop goes in by direct sowing rather than being raised under cover, timed for spring across April to May or for the late-summer window from late July into early September. Begin by coating the seed with a matching Rhizobium so the plant can fix its own nitrogen, then set it a quarter to half an inch deep, slightly lower in sandy ground, across a firm, well-drained, near-neutral bed. Expect a first cut around 60 days on, with the stand reaching its full body over what remains of the seeding year. A single firm principle underpins all of it: do not return alfalfa straight into a spent alfalfa field, since autotoxicity will undo the young stand.

Myths

Myth

Alfalfa is widely supposed to be poisonous and unfit to feed to animals or people.

Reality

Far from it: this is a safe, nourishing forage offered to livestock and rabbits, taken by people as a supplement, and worked into certain pet diets, and it has never appeared on any ASPCA toxic-plant list. The lone real qualifier concerns frothy bloat in cattle and sheep moved onto a heavy stand, together with the occasional photosensitization and a trace of phytoestrogen. Not one of those things makes it poisonous to pets or people.

Sources