Roundup recommends waiting at least seven days after application of Roundup Weed and Grass Killer products when re-seeding a lawn area. The product will kill weeds or grass in any area where it is applied and caution is advised when spraying near plants that you intend to preserve.
Roundup recommends not mowing the area before application and advises that the area should be watered both before application and after two or three days. If green patches remain after seven days, another treatment can be applied. The area should not be raked or tilled for at least three days after the weed killer has been sprayed for the final time.