Black medic has yellow flowers that later produce clusters of black fruit.
Black medic (Medicago lupulina) is a bothersome weed in flower beds, lawns and even in cracks in sidewalks or between pavers. It is usually a low-growing annual plant but it can grow to about a foot wide and tall in various sites. It has small, clover-like leaves composed of three leaflets attached to very fine stems. Probably the most striking feature of this plant are its tiny, clusters of bright yellow flowers that begin to appear in early summer and continue until a hard freeze kills the plant. After the flowers fade, clusters of nearly black fruit develop in their place, each one containing a single seed. While black medic is usually an annual plant, it can sometimes be a short lived perennial as well.
The challenging aspect of controlling black medic occurs in flower beds and borders. Young plants usually go unnoticed as they often grow up amongst the foliage and stems of other plants. This makes them difficult to see and pull out because it is hard to find the base of the plant where all the stems are attached to the main tap root. Pulling on the side branches usually means that they just break off. Each plant can produce hundreds of seeds so it only takes a few plants to create a significant infestation of this weed. Besides pulling, hoeing out the young seedlings can be effective but often difficult in a densely planted flower bed. Applying an organic mulch 2 to 3” deep, around the flowers, to cover the soil and any weed seeds that might be there, may also be helpful.
Black Medic in Lawns
Black medic can also be a problem weed in lawns, particularly lawns that have not been adequately fertilized or are stressed for other reasons. Properly fertilizing the lawn and increasing the mowing height will help make the lawn grasses more competitive with the black medic. Most broadleaf lawn herbicides will also help control the problem in lawns. These same products or a non-selective herbicide, like glyphosate, can be quite effective in controlling black medic in sidewalks and pavers.