St. Augustine grass (Stenotaphrum secundatum) is a warm-season turfgrass known for its coarse texture and thick blades, thriving primarily in the Southern United States. Proper mowing is essential for the lawn’s density, color, and health. Cutting frequency must be managed to prevent stress and encourage robust growth. Adherence to height and frequency rules ensures the turf remains resilient against disease and weeds.
Establishing the Optimal Cutting Height
The proper height for St. Augustine grass directly affects the root system and heat stress management. Experts recommend maintaining the grass between 3 and 4 inches throughout the growing season. This high setting allows blades to produce energy through photosynthesis, supporting deeper root development.
Taller blades create a self-shading effect on the soil and surface runners (stolons). Shading the soil helps conserve moisture and keeps the crown cooler during high temperatures. In dense shade, adjust the height to 4 to 4.5 inches to maximize leaf surface area for capturing limited sunlight.
Cutting the grass too short, known as scalping, is damaging. St. Augustine grass spreads horizontally via stolons. Scalping removes photosynthetic material, injuring these surface runners, stressing the plant, leaving it vulnerable to pests and heat.
The One-Third Rule and Mowing Frequency
The “One-Third Rule” dictates that you should never remove more than one-third of the grass blade’s total height in a single cutting session. This practice minimizes shock to the plant, ensuring enough leaf tissue remains for quick recovery and continued growth. If your target height is 3 inches, you must mow the lawn before it exceeds 4.5 inches tall.
During the peak growing season, St. Augustine grass requires mowing every 5 to 7 days. If the lawn grows from 3 inches to 4.5 inches in one week, a weekly cut is necessary. During periods of slower growth, the frequency can be reduced to every 10 to 14 days.
Leaving the grass clippings on the lawn, called grasscycling, is beneficial when adhering to the One-Third Rule. Since only a small portion of the blade is removed, the clippings are short and decompose rapidly. This returns nitrogen to the soil, contributing to the lawn’s vigor and reducing the need for fertilization.
Adjusting the Schedule for Seasonal Growth
St. Augustine grass is a warm-season variety; its growth rate fluctuates with environmental changes, requiring a flexible schedule. During summer, when temperatures are consistently between 80°F and 95°F, the grass grows fastest. This peak season necessitates the most frequent mowing, typically weekly, to maintain the desired height.
As the season transitions into the cooler shoulder months of spring and fall, the growth rate naturally slows down. This allows the mowing frequency to decrease, often shifting to a bi-weekly schedule. Factors like fertilizer application and irrigation also accelerate growth, meaning a well-fed lawn requires more frequent cutting than one receiving minimal inputs.
Areas receiving substantial shade will grow slower than sections in full sun. These shaded sections require less frequent mowing, but the height should be kept higher, typically 4 inches or more, to compensate for the reduced light intensity.
Mowing During Stress and Dormancy
Mowing must be modified or halted when St. Augustine grass is under severe environmental stress or dormant. When subjected to extreme heat or drought, the plant diverts energy to survival, and mowing should be minimized. If a cut is necessary, the height should be raised to 4 inches or more to preserve moisture and protect the stolons.
In regions with cold winters, St. Augustine grass enters dormancy, causing blades to turn brown. Mowing should stop when the turf is dormant, typically when soil temperatures drop below 55°F. If a final cleanup cut is desired before winter, use the higher end of the range to insulate the crown.
Disturbing the grass during these periods can hinder its ability to recover. A higher cut helps protect the plant from winter desiccation (excessive moisture loss). Once the grass actively greens up in the spring, a lower initial cut can remove dead winter material before returning to the normal maintenance height.