What were those interesting yellow flowers in the lawn? Or, this time of the year, what are those interesting little black clusters of seeds? Black Medic (Medicago lupulina), also known as black clover, yellow trefoil, or hop medic, is an introduced species, related to clover. While it’s found as a weed throughout Montana (the rest of the US, and Canada), it’s actually native to Europe.
Like other members of the pea family (e.g. alfalfa & sweet clover), it is a nitrogen-fixing species. This means that Black Medic plants have symbiotic bacteria that take nitrogen (a vital element for plant growth) out of the air and deposit it into the soil in a form that plants can use. This is good for surrounding plants, as well as for the Black Medic.
Black Medic produces vast quantities of seeds, and can easily take over sparse lawns. It grows well in compacted soil, or soil that is low in nitrogen. In fact, if it does better than the grass, it may indicate that the soil is lacking in nitrogen.
Management of Black Medic should include high mowing, fertilization (it likes soil with little nitrogen) and irrigation. Reducing soil compaction would also be beneficial. Mowing black medic will not kill the plant.
Black medic apparently has edible uses, theoretically as a pot herb (stir-fried or in stews). The seeds can be sprouted and eaten like alfalfa sprouts. Of course, like clover and alfalfa, it’s rather high in fiber, which means eating it in large quantities is likely to have unpleasant side-effects.