Sweetclover Seed — Yellow & White

Melilotus officinalis (yellow sweetclover) and Melilotus alba (white sweetclover) are biennial legumes in the pea family, native to Eurasia and introduced to North America in the 1600s–1700s. They naturalized aggressively across the continent and became a primary nitrogen source for Great Plains dryland farming before synthetic fertilizers became widely available in the mid-20th century. As biennials, sweetclovers follow a two-year life cycle. In year one, the plant germinates, develops a deep taproot, builds a rosette, and stores energy reserves. It overwinters in a vegetative state. In year two, it elongates rapidly in spring, produces an abundant bloom (white or yellow depending on species) through summer, sets seed, and then dies. The entire nitrogen contribution and the full bloom—including its value as bee forage—is a year-two event. The taproot is extraordinary in length for a legume. At up to about 5 feet, it accesses subsoil moisture and minerals unavailable to shallow-rooted clovers and vetches, and it physically conditions compacted subsoil layers in a way that smaller-rooted species cannot achieve. When this taproot system decomposes after the plant dies, it leaves substantial biopore channels that improve drainage and aeration in the subsoil. The combination of deep root action and large nitrogen fixation over two seasons makes sweetclover one of the most agronomically productive biennial cover crops available.