How to Grow Alfalfa: Lime First, Then Years of Cutting

Alfalfa is a perennial legume that roots ten to fifteen feet down, fixes its own nitrogen and crops for years. It also fails on acid soil — and that is a decision you make before sowing, not after.

pH decides it

This is the step that separates a stand that crops for six years from one that never establishes.

Alfalfa wants 6.5 to 7.0. Below about 6.2 it struggles, and on genuinely acid ground it fails — partly because the Rhizobium bacteria it depends on for nitrogen fixation do not thrive there either.

Feed it, just not nitrogen

Alfalfa supplies its own nitrogen through root nodules. Adding nitrogen fertiliser is wasted money and can actually suppress fixation.

But taking several cuts a year removes a great deal of phosphorus and potassium, and alfalfa is a heavy user of both. Follow a soil test, and retest every few years on an established stand.

Site: deep and well drained

The ten to fifteen foot taproot is where the drought tolerance comes from — and it is also what the site has to allow.

Shallow soil over rock, a high water table, or a compacted pan all stop that root developing. A stand on such ground never achieves the drought tolerance alfalfa is known for, and it will not last.

Sowing

1. Inoculate the seed — pre-inoculated, or treat it yourself. Essential on ground that has not grown alfalfa before
2. Fine, firm seedbed. The seed is tiny and needs soil contact; loose cloddy ground gives a thin stand
3. A quarter to half an inch deep, no more
4. Spring in cold regions, late summer in milder ones — but allow six weeks of growth before frost
5. Control weeds in year one. Established alfalfa competes well; seedlings smother easily

Cutting, and the two timing rules

Cut at early bloom — about 10% of the stand flowering.

Earlier gives richer, higher-protein forage, and it draws down root reserves faster, which shortens the life of the stand. Much later gives coarse, stemmy material. Early bloom is the compromise that keeps both quality and longevity.

Stop cutting six weeks before the first hard frost. The plants need that window to rebuild root reserves for winter. A late final cut is the single commonest cause of winter kill.

How long it lasts, and why you cannot patch it

Four to six years typically, sometimes eight or more with good management.

One thing worth knowing: alfalfa is autotoxic — it suppresses its own seedlings. So you cannot thicken a thinning stand by reseeding into it. When a stand goes, it is rotated to something else for a year or two before alfalfa returns.

In a garden

A good cover crop for ground you can rest for a season or more: the taproot breaks compaction and the plant adds nitrogen.

But it is a perennial and slow to establish, so it suits a bed being rested rather than a gap between vegetables. For a short window, clover or field beans do the same job far faster.