Depends on many things, type of grass, your location, what do you want the lawn to look like, broadleaf or other weed problem, your budget, etc. Some types of fertilizer is for spring, some for summer, some for weed control and others for fall. In fact there are even fertilizers used in the south for the months we call winter in the north. Your best bet is to contact your local extension agent or a good landscaper in your area. We would only be guessing as to what your condition and wants are.