Alfalfa

Value to bees

Nectar

High

Pollen

High

As a honey crop

Major honey crop — yields a surplus in good years

Which bees, and why

The single most instructive bee-plant relationship in the catalogue. The alfalfa keel is held under tension and releases explosively when a bee's weight triggers it, hitting the insect on the head with the staminal column. Honey bees find this aversive and rapidly learn to approach from the side, taking nectar and tripping nothing. Alfalfa grown for seed is therefore pollinated commercially by alfalfa leafcutter bees (Megachile rotundata) and alkali bees (Nomia melanderi), which tolerate being tripped and are managed in vast numbers for the purpose. The honey producer and the pollinator are different animals.

A keel flower requiring force to open, and the force is what a honey bee is avoiding. This is a case where flower architecture selects not by tongue length but by tolerance.

Worth knowing

Excellent forage on paper, and the tripping mechanism complicates it in practice: a honey bee robbing nectar from the side of the flower collects no pollen and delivers none.

Flowering

In flower

June to September (northern hemisphere)

A long potential window, repeatedly interrupted: alfalfa cut for hay is cut in bloom, so the flow ends abruptly whenever the mower arrives. Seed crops are left to flower fully.

When nectar flows

Secretes best in hot dry weather with irrigation beneath it, which is exactly the condition of the irrigated American west where most of the honey comes from.

Year-to-year variation

Depends less on weather than on farming decisions. The honey crop follows the acreage left to flower rather than the acreage grown.

What it does to the honey

Alfalfa nectar produces a mild, pale, clean honey close enough to clover that most tasters cannot separate them. Its contribution to the catalogue is volume and neutrality rather than character.

Growing it

Conditions

Deep, well-drained, neutral to alkaline soil, full sun, and — for commercial yields — irrigation. Drought-tolerant once the taproot is down.

Size

60-90 cm, with a taproot that can reach several metres.

Native range

Central and southwest Asia, cultivated for at least three thousand years and now grown on every inhabited continent.

Suits

Meadow or wildflower area, Farm scale

• Sown as part of a herbal ley or green manure it fixes nitrogen and feeds bees at once, provided it is allowed to flower before cutting.
• The single most useful thing a grower can do for bees on alfalfa is to delay one cut past flowering. That decision, not the crop's presence, determines whether it is forage.

What it looks like

A deep-rooted perennial legume with clover-like trifoliate leaves and short spikes of small purple, occasionally yellow or variegated, pea flowers.