Grass clippings are a natural fertilizer for your lawn. Not only do clippings have a heavy moisture content, which adds water to your turf, but they decompose quickly and provide nutrients that will nourish the soil and root system.
Once established, you only need to fertilize your lawn in the fall if you “cut it and leave it!” According to Rutgers Cooperative Research Extension “fertilizing your lawn late in the season (September through November) the previous year reduces or eliminates the need for fertilizer in the spring, reduces frequency of mowing, and improves drought resistance.” Fertilizing in the fall allows the roots system to establish while spring fertilizing promotes top growth, which requires more frequent mowing and can actually stunt root growth. Be careful not to fertilize your lawn if heavy rain is in the forecast. Instead of soaking into the soil where it can nourish your lawn, the fertilizer is likely to simply wash away with the stormwater and find its way to local waters causing algae blooms and leading to proliferation of jelly fish.
Maintaining a mowing height of 2½ to 3½ inches will help increase drought resistance and will decrease insects and disease damage. Turf that is kept at a height of 2 inches or less decreases drought and heat resistance and increases the incidence of insect and disease damage as well as weed invasion. (“Your Lawn and its Care”, Rutgers Cooperative extension FS102, https://njaes.rutgers.edu/fs102/)