Keep your mower blade sharp. Dull blades* tear grass instead of cutting it. Lawns mowed with dull blades use 30 percent more water. Plus the wounds created by dull blades allow disease pathogens to enter grass plants. File your blade regularly and replace damaged blades.
Leave the clippings. Clippings do not create thatch or mulch,* contrary to popular belief. If you cut only a third of the plant at each mowing, the clippings won't smother the grass either. Mulching mowers work best to chop up clippings so they can work their way through the grass and onto the soil surface. There, earthworms incorporate clippings into the soil, improving both its drainage after storms and its ability to hold water during droughts. Do not disperse clippings onto pavement or into gutters. They are high in phosphorus and can cause pollution when they’re washed into storm sewers and enter streams and lakes.
Don't fertilize early. Fertilizing in early spring only causes extra stress on grass plants over the long term by encouraging excessive top growth at the expense of their roots. (Do not apply fertilizer to frozen soil, saturated soil, or on top of snow. It's a waste of fertilizer and a sure way to have it wash into streams and lakes, thereby polluting the environment.) A better strategy is to fertilize in the fall, from early in the season until about 2 weeks after the last mowing. Plants will use this fertilizer to develop root reserves to help them survive through winter and get off to a healthy start next spring.
Watch your water. It's easy to do more harm than good. Never water at night. Wet grass invites diseases. Water between 4 a.m. and 8 a.m. when the leaves will dry quickly in the morning sun. During extended drought, stop watering and allow grass to go dormant.
Special care in the shade. Grass needs a minimum of 4 hours of direct sun -- 6 hours if it gets much foot traffic. Consider other ground covers if your lawn receives less than this. In shady spots, plant fine fescues that are adapted to lower light. Mow high and reduce fertilizer.
Spray sparingly. Never use lawn insecticides without checking to see if the problem really requires treatment. Seventy-five percent of lawn insecticide applications in urban areas are unnecessary or ineffective. Manage your grass properly for healthy root systems that can tolerate some insect damage and remain aesthetically pleasing.
Fill in weak spots. Use a rake to work up and improve the soil where weeds flourish or where the ground is bare. Then re-seed with the grass varieties that are best suited to the site. If, after a season of mowing high and leaving the clippings (taller grass will help shade out weeds,) your lawn is still over fifty-percent perennial weeds and bare spots, consider a complete renovation of your lawn.