A healthy, rhizome-based lawn is a good barrier to choke out weeds and foreign grasses. For an established lawn, check with a local nursery for when and what to use to fertilize (usually about 1 pound of nitrogen per 1000 square feet, watered immediately) to get the fertilizer close to the roots. Depending on climate, about an inch of water per week will suffice. It’s better to water deeply and over a longer period of time than shallowly and frequently. Mowing in the spring will help bring your lawn out of dormancy. Mowing causes the grass to shift more energy to growing blades than growing roots. Never cut more than one third of the blade off when you mow. Clippings will return the nutrients and water to the soil as long as they are not so thick as to prevent sunlight from reaching the lawn below.