Most grasses have a range of recommended mowing heights. Stay at the upper end of that range when the lawn is under stressful conditions, such as hot weather or drought, or if you have a shady lawn. In cooler weather, you can cut the grass a little lower.Follow the one-third rule. For a thriving lawn, never cut away more than one-third of the grass blade in any one mowing. If the grass “gets ahead of you” because of wet weather or your busy schedule, move up the cutting height of your mower to the highest possible setting and mow. If clippings are too long and heavy, even at that cutting height, catch them with the bagging unit or clean up after mowing with a leaf rake. Then move the cutting height back to your normal range and cut the lawn again a few days after that first mowing. Edging and trimming are the finishing touches of mowing, kind of like getting a shave after you’ve had a haircut. Edging and trimming are pretty close to being the same thing. Some tools are called edgers because they’re designed to trim the lawn along a hard surface like a driveway or sidewalk. Edgers cut a nice clean edge, but leave some dirt and grass debris that you need to clean up. On the other hand, you can use trimmers anywhere — along a hard surface, in tight spaces, next to planting beds, and so on.