St. Augustine grass is a warm-season turfgrass popular in southern climates, known for its wide, coarse blades. It spreads aggressively through above-ground runners called stolons, creating a dense lawn when properly maintained. Adhering to the correct mowing height is the most important maintenance factor governing the grass’s overall health, density, and drought tolerance.
The Ideal Height for Healthy St. Augustine Grass
The recommended cutting height for St. Augustine grass is 2.5 to 4 inches, which is higher than many other warm-season varieties. Maintaining this height influences the grass’s physiological health. Most professionals recommend keeping the grass closer to the upper end, typically 3 to 4 inches, for optimal results.
Taller blades maximize photosynthesis by capturing more sunlight, which produces the plant’s energy. This energy supports the development of a deeper root system. A deeper root structure enhances drought resistance, allowing the turf to access moisture and nutrients deeper in the ground during dry spells.
The dense, tall canopy created by higher mowing protects the soil and runners. The shade helps cool the soil surface and reduces water evaporation, retaining moisture. This shading effect also suppresses weed germination, as most weed seeds require direct sunlight to sprout and establish themselves. Cutting the grass too short removes this protective canopy, stressing the plant and making it vulnerable to heat, drought, and weed invasion.
Seasonal and Shade Adjustments to Cutting Height
The ideal mowing height should be adjusted in response to changing environmental conditions. During peak summer heat or drought stress, raise the cutting height to the highest setting, often 3.5 to 4.5 inches. This maximizes the soil-shading effect, insulating the root zone and protecting the plant from excessive heat.
Grass growing in heavy shade requires adjustment to compensate for limited light. In these low-light environments, the grass should be cut at the higher end of the range, typically 3 to 3.5 inches. The increased blade length ensures the plant captures maximum surface area of scarce sunlight for energy production. Keep the height high enough to prevent the grass from drooping over, which can cause matting and reduce light penetration.
In preparation for cooler months, a slight adjustment can be made for the final cut of the season before the grass enters dormancy. Lowering the deck slightly, perhaps to the 2.5-inch mark, helps remove older, dead leaf material. This practice is done only once near the end of the growing season to prepare the lawn for winter, and the regular, taller height should be maintained throughout the active growing period.
Mowing Frequency and Preventing Scalping
Mowing frequency is linked to cutting height through the “One-Third Rule.” This rule dictates that you should never remove more than one-third of the grass blade’s total height in a single session. For example, if your desired cutting height is 3 inches, mow the lawn when it reaches 4.5 inches, removing only 1.5 inches of growth.
St. Augustine grass is sensitive to the shock of removing too much leaf tissue at once. Exceeding the one-third rule results in “scalping,” which severely stresses the turf and exposes vulnerable stolons and stem tissue. Scalping forces the plant to use stored energy reserves to regenerate the lost leaf surface, weakening the root system and making the grass susceptible to disease and pests.
Mowing frequency must be determined by the grass’s growth rate, which varies based on temperature, fertilizer, and rainfall. During the peak growing season, typically spring and summer, mowing once a week is necessary to adhere to the one-third rule. During cooler periods when growth slows, the frequency can be reduced to every two weeks or less.
Regardless of frequency, use a sharp mower blade to ensure a clean cut across the wide leaf blade. A dull blade tears the grass, leaving ragged edges that turn gray or brown. This stresses the plant and provides an easy entry point for disease pathogens. Maintaining a sharp edge minimizes damage, allowing the grass to heal quickly and devote energy to healthy growth.