Choosing a type of grass that is best-suited to your soil is a crucial step to having a healthy green lawn. With proper care, the lawn can help improve the soil over time, but you'll need the right seed to get you started. With very poor soils, you might have to amend them with sand to improve drainage or organic material to improve tilth for your lawn to be successful.
Sandy soil is one that is very heavy in large sand particles. These types of soil are not very dense, tend to be low in nutrients and do not hold moisture well. To test if your soil is sandy, squeeze some in your hand and watch what happens when you let go. Sandy soil usually feels dry and will easily fall apart. It can be improved over time with the addition of compost, aged manure, mulch or other organic materials. Lawns on sandy soil should be drought-tolerant and might require more frequent watering. Grass types that tolerate sandy soil include fescues, which are cool-season varieties, and warm-season cultivars like Bermuda, Bahia and Zoysia.
Clay soil contains a lot of small particles of rock sediment. If you squeeze it in your hand, it will keep its ball shape when you open your hand. Although rich in minerals, clay soil is like sandy soil in that it lacks sufficient organic material. It also drains very poorly, and water can sit for days, depending on how high the clay content is. Additions of greensand will break up the clay and improve drainage; compost, leaf mulch and aged manure will improve its fertility and structure. Even the grass's roots will help improve the clay over time. Ryegrass is a cool-season variety that often does better in very moist conditions and can tolerate standing water for several days. Most warm-season grasses will not fare well in hard clay. If you're not fixated on the “perfect” lawn, consider adding some clover seed to your grass to improve the soil over time. Clover not only adds a bit of color, its roots fix nitrogen in the soil and help break up the clay.
Loam is the ideal soil for all grasses. Most topsoil is, in fact, a type of loam that can either be on the sandy side or the clay side of the spectrum. Loamy soil will form a loose ball when pressed in your hand, and the ball will come apart in large chunks when you let go. Loamy soil will not need as many amendments as soils that are heavy clay or sand, though they do benefit from regular additions of organic materials to compensate for what the grass takes away. Lawns that are grown in 8 to 10 inches of loam are healthy, disease-resistant and deep verdant green.