St. Augustine grass (Stenotaphrum secundatum) is a warm-season turfgrass common throughout the Southern United States, prized for its thick, dense growth and broad, flat leaf blades. It spreads via aggressive, above-ground runners called stolons. Maintaining the correct mowing height is the most important factor for achieving a healthy, robust St. Augustine lawn.
The Ideal Mowing Height
The recommended general mowing height range for St. Augustine grass is between 2.5 and 4 inches during the active growing season. Most turfgrass specialists suggest aiming for the higher end of this range, particularly 3 to 4 inches, to promote maximum plant health. Cutting the grass below 2.5 inches places significant stress on the turf and is a common mistake. Lower heights force the plant to divert energy away from its root system to regrow leaf tissue, weakening its overall structure.
Physiological Benefits of Taller Grass
Maintaining a taller canopy directly supports the development of a deeper, more resilient root system. Grass plants maintain a proportional relationship between the height of the leaf blade and the depth of the roots. Taller blades allow the plant to produce more energy through photosynthesis, which in turn fuels the growth of deeper roots that are better able to forage for water and nutrients. Deeper roots are particularly beneficial for St. Augustine grass, improving its natural tolerance to drought and heat stress by accessing moisture deeper within the soil profile.
The increased leaf surface area also plays a role in water conservation by providing a natural shading effect on the soil. The taller grass canopy acts like a living mulch, reducing the surface temperature of the soil and slowing the rate of water evaporation. This helps the soil retain moisture for longer periods during high summer temperatures. Furthermore, a dense, taller stand of St. Augustine grass is highly effective at suppressing weed growth. The thick canopy blocks the sunlight necessary for the germination and growth of many common weeds, such as crabgrass, reducing the need for chemical herbicides.
Taller growth also protects the grass’s unique above-ground runners, or stolons, from damage. Cutting the grass too low can “scalp” the lawn, damaging these stolons and leaving the turf susceptible to disease and pests.
Mowing Technique and Frequency
To maintain the ideal height without stressing the grass, it is important to strictly follow the “one-third rule.” This rule dictates that no more than one-third of the grass blade’s total height should be removed in any single mowing session. For example, if the desired height is 3 inches, you should mow when the grass reaches approximately 4.5 inches tall. Removing too much leaf material at once forces the plant into a state of shock, severely limiting its ability to photosynthesize and recover.
The one-third rule dictates the necessary mowing frequency, which often means mowing once a week during the peak growing season, generally late spring through summer. If the grass is growing quickly due to rain and fertilizer, you may even need to mow every five days to stay within the recommended removal limit. Mowing frequency can be reduced during cooler months or periods of drought when growth naturally slows down.
Using a mower with a sharp blade is also important for the health of St. Augustine grass. A dull blade tears the coarse, wide leaf blades instead of cleanly cutting them, leaving jagged ends that turn brown and increase the plant’s vulnerability to disease. Blades should be sharpened regularly, typically after every 25 hours of use, or at least once at the beginning of the growing season.
Mowing height may require slight seasonal adjustments to prepare the turf for dormancy or stress. During periods of extreme heat or drought, raising the cut height to the upper end of the range, around 4 inches, helps maximize shading and root protection. Conversely, a final cut before winter dormancy can be slightly lower, around 2.5 inches, to remove excess leaf material, but should never dip below that level.