July 14, 2012
I have received some question lately on the yellow flower that is showing up in lawns in midsummer. The plant is Bird’s-foot Trefoil (Lotus corniculatus). In past years, it has been included in roadside mixtures in Iowa and has spread to lawn areas. It is not unusual to see it along curb sides as in the picture below. It is a perennial, but most people do not notice it until late June when it begins to flower.
It is a legume and has a flower similar in shape to the Pea. Personally, I think it is very attractive. According to an article in Wikipedia, the fresh tissue contains cyanogenic glycosides, which are toxic to humans. I have never tried to eat it, but I don’t think that it presents any danger to humans. It is a forage, and cattle often graze on it.
Being a clover-like broadleaf, it is controlled by most of the same broadleaf herbicides that control clover. It is generally observed in lawns that have not been treated with broadleaf controls. If you want to get rid of it, I would wait until fall and treat with broadleaf herbicides. It will be gone next year. The reason for waiting, is that these herbicides will easily damage other landscape plants at this time of year.
Bird's-foot trefoil in a curb area in central Iowa.