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 goosegrass, dallisgrass, chickweed, henbit and oxalis. This product contains an advanced herbicide known as Dimension® that provides post emergence control, meaning it will kill existing weeds, such as crabgrass, even after they germinate. Post emergence control is limited to crabgrass and is effective for up to four weeks post-germination. It will only kill the plant up to the three-leaf stage of growth, a fully mature crabgrass plant has 7-leaves.