The most important part of turfgrass is the part you can't see. Healthy crowns and roots improve not only the appearance of the grass plant but its chances for survival through the heat and drought of mid-summer. Roots support the crown from which leaves grow and specialized roots called "stolons" or "rhizomes" creep along the surface, starting new crowns. Growing good grass roots depends on the tasks associated with planting and maintenance.
Cultivate topsoil at least 10 inches deep; sandy loam or well-drained loam allows roots to stretch and grow more freely. Work in at least 2 inches of compost mixed with manure or peat moss to improve soil texture and provide a ready source of organic nitrogen for new lawns. Add lime or sulfur to correct pH to between 6.0 and 7.0 before planting lawns.
Keep soil--not top growth--moist. Grass needs at least an inch of water weekly. Water lawns infrequently but deeply to encourage deep root growth; watering less deeply attracts roots to the surface, exposing them to heat and dry conditions. Keep roots moist and growing by watering grass until the first frost.
Mow frequently and keep grass at the right height for the variety. Grass with large crowns or clumps, like Kentucky bluegrass or tall fescue, should be mowed taller. Warm season grasses like centipede or zoysia grass prefer shorter mowing. Whatever the variety, mow no more than one-third of the blade lengths at a time to stimulate growth and keep roots sheltered.
Fertilize at the end of the growing season for strong root growth; fall for cool-season grasses, spring for warm-season grasses. Nutrients from fertilizer go into top growth at the beginning of the season, but roots set the stage for next season's growth as top growth enters dormancy. Use a fertilizer that is balanced for your area's soils and apply it at the rate dictated on the package instructions.
Give roots plenty of room by keeping weeds pulled and aerating periodically. Weeds have aggressive root systems that can choke turfgrass roots, particularly during periods of stress or dormancy. Aerate soil to get air and water to roots.