Alfalfa is a perennial forage legume which normally lives four to eight years, but can live more than 20 years, depending on variety and climate. The plant grows to a height of up to 1 metre (3+1⁄2 feet), and has a deep root system, sometimes growing to a depth of more than 15 m (49 ft) to reach groundwater. Typically the root system grows to a depth of 2–3 m (7–10 ft) depending on subsoil constraints.

Alfalfa is a small-seeded crop and has a slowly growing seedling, but after several months of establishment, it forms a tough “crown” at the top of the root system. This crown contains shoot buds that enable alfalfa to regrow many times after being grazed or harvested.