Green Foxtail One type of annual grass weed is green foxtail. It is a common weed across the country, appearing in gardens, lawns, and agricultural fields. The leaves of Green Foxtail grow to a maximum height of three inches and a width of half an inch. This plant has a whip-like seed head that is covered in numerous tiny bristles with dark green tips. Its name originates from its fibrous roots and foxtail-like seed head.