Medium Red Clover (Trifolium pratense)
Source seeds from Johnny's Selected Seeds
Red Clover is not only a cover crop, but as a legume it is also a nitrogen fixer. I buy the seeds that are pre-coated with the rhizobacterial inoculant (otherwise you will need to buy the inoculant and coat yourself, as our soil do not have natively have rhizobacteria and the legume cannot fix nitrogren without the rhizobacteria present). The leaves are pretty and very slightly variegated. They make these lovely light lavender flowers when mature.