Dave Powell, USDA Forest Service (retired), Bugwood.org
White clover is a winter perennial with leaves that group in threes and typically, but not always, have white or lighter green bands and toothed edges. Sometimes there are four leaves in a group, which is considered lucky by those who find them in the yard. This weed produces white flowers, sometimes with a pink tinge, and it most actively grows in cooler temperatures but can be seen year-round in most places.
Most clover will survive winter frosts and still take hold in spring and summer. Use a postemergent herbicide containing triclopyr or florasulam to clean up any left over clover from the prior season. To avoid a clover infestation, apply a pre-emergent herbicide in early fall or late winter before the seeds germinate.