What Is the Depth of Roots of St. Augustine Grass Roots?

Root Development

St. Augustinegrass grows its fibrous roots wherever ample moisture and nutrients exist in the topsoil. Tolerant of wet, slightly mucky soils, this grass grows its roots only 2 to 3 inches deep in such conditions, or when irrigation is frequent and fertilizer constantly applied. However, an evenly moist soil well below the grass encourages roots to grow more deeply into the soil for obtain moisture and experience cooler, consistent temperatures any time of year.

Depending on growing conditions, St. Augustinegrass develops roots mainly in the top 12 inches of soil. The roots grow only where necessary to access water and moisture. In sandy soils, water and nutrients readily drain or leach, causing grass roots to grow more deeply, usually in the 8- to 10-inch range. In heavier loam and clay soils, roots may only penetrate into the 4- to 8-inch range because of soil particle density and slower downward movement of water and nutrients.

St. Augustinegrass lawns that are irrigated infrequently but deeply develop roots that are much deeper penetrating than are those irrigated regularly with light amounts of water. Regular and light waterings encourage roots to stay near the soil surface where the water always exists. By contrast, deeper-penetrating and longer irrigation events encourage grass roots to grow downward to find moisture. Therefore, the grass becomes more tolerant of heat and drought since deeper soil moisture sustains the grass longer before needed irrigation.

Keeping a St. Augustinegrass lawn mowed at the proper height also encourages deeper root growth. Never mow this type of turf grass shorter than 2 inches and never cut off more than one-third of the total height of the lawn at any one mowing. Cutting the grass too short exposes the lower stems and topsoil to more sunlight, heating the soil and causing faster soil dry-out. St. Augustinegrass mowed as high as 3 to 4 inches encourages deep root growth because the extra food made in photosynthesis by the longer leaves fuels more root growth below. The longer lawn also shades itself and the soil better, keeping temperatures cooler and slowing the rate of soil drying.