The speed at which your fertilizer will begin to work is based on the type of fertilizer you choose to use. Fast-releasing fertilizers will work more quickly, in good growing conditions you can expect to see improvements to your turf within two to four days of application. Note that you will likely need to apply a quick-releasing formula more frequently than the controlled-release blends of fertilizer. The controlled-release formulas will gradually break down into available nutrients, and will take three to ten weeks to improve your lawn.