Medics grow best during the warmer conditions of autumn and spring, but a wet autumn will give a good bulk of feed for winter. This free-seeding annual legume is a low-growing species, prostrate but not rooting from the nodes. Barrel medics flower in spring after a `vernalisation' period of cold weather, producing small, yellow flowers that give rise to a spiral burr containing 6-10 seeds. The burr has straight spines, and can be combed from wool.
Medics are adapted to a Mediterranean climate with dry summers. They survive wet summers in the subtropics because of their hard seed, but with enough softening to allow regeneration in autumn. In permanent pastures, medics suffer from competition in autumn from the summer growth of grasses. Reducing this by heavy grazing in autumn, summer drought or by cultivation improves seed germination.