Jonathan Green Crabgrass Preventer plus Green-Up Lawn Fertilizer feeds the lawn for up to three full months and provides pre-emergent control of crabgrass. When applied prior to germination it controls other weeds such as goose grass, dallis grass, chickweed, henbit and oxalis. Postemergence control is limited to crabgrass and is effective for up to four weeks post-germination. It will only kill the plant up to the 3-leaf stage of growth; a fully mature crabgrass plant has 7-leaves. Thoroughly irrigate the treated area after application for best results. About 1-1/2 inches of water per week is sufficient between rainfall and irrigation, but not to the point of run-off.