Alfalfa

What it is. Alfalfa, also called lucerne, is a herbaceous perennial legume with a deep taproot and clover-like green leaves. It produces small purple flowers in summer, followed by flat, pea-like fruits.

Uses. It is grown in many countries as animal feed or as a green crop, and it can improve soil nutrient levels and soil structure. As a legume, it fixes nitrogen from the air with the help of bacteria on its roots.

When and how to sow. Sow the seed in a firm seedbed, about ¼ to ½ inch (0.6 to 1.3 cm) deep. Heavy soils call for no deeper than ¼ inch (0.6 cm), and light soils for no deeper than ½ inch (1.3 cm).

Sources differ on timing. One gives autumn as the time to sow seed, while another says early spring or late summer. Check your local last frost date and advice before choosing.

Inoculate the seed first. Alfalfa seed should be inoculated just before sowing to supply the nitrogen-fixing bacteria it needs. Most commercial seed comes pre-coated, but pre-inoculated seed should be re-inoculated if it isn’t used within 6 months.

Soil. Alfalfa will grow in most situations, including poor, dry soil. Nitrogen fixation falls as soil pH drops below 6.5, so keep the pH near neutral.

Replanting. Sowing alfalfa into an old alfalfa patch is very hard to do successfully because of autotoxicity.

Feeding. Nitrogen fertilizer is usually unnecessary for alfalfa, since it fixes its own nitrogen. Phosphorus tends to be the nutrient most likely to limit yields. Placing a starter fertilizer about an inch below the seed can give seedlings a head start.

Soil testing and lime. Test the soil before planting, since it is much more effective to fix nutrient gaps before sowing than after. Lime is needed on soils with a pH below 6.5.

Pests and diseases. Alfalfa may be susceptible to alfalfa weevil, leafhoppers, spotted aphids and bacterial wilt. Removing fall growth may reduce the severity of alfalfa weevil the following spring.

Grazing. Begin grazing when the alfalfa is about 6 inches (15 cm) tall. In fall, avoid grazing hard within 5 to 6 weeks of the first killing frost, and leave at least a 4-inch (10 cm) stubble.

Bloat in grazing animals. Bloat may be a problem when animals graze young, lush alfalfa. Fill animals with another roughage before turning them onto alfalfa for the first time.