St. Augustine grass is a popular warm-season turfgrass across the Southern United States, particularly in warm, humid climates like Florida and Texas. It is appreciated for its coarse texture and thick, carpet-like appearance. Its growth speed depends heavily on environmental and management factors, requiring an examination of both vertical leaf growth and horizontal spreading rate.
Defining the Growth and Spreading Rate
St. Augustine grass exhibits growth in two distinct ways: vertical growth of the leaf blades and horizontal spreading by above-ground runners, called stolons. The speed of growth is highest during the peak growing season, which generally aligns with the summer months. Vertical growth necessitates mowing and can be rapid when conditions are ideal and the grass is properly fertilized.
Horizontal spread allows the grass to form a dense mat and fill in bare areas. St. Augustine grass is considered a fast-spreading turf, with its stolons capable of growing several inches per week during periods of vigorous activity. This horizontal growth is often more significant for establishing a thick lawn than the upward blade growth. Under optimal conditions, the total lateral spread can average between 6 to 12 inches over the course of an entire year.
Environmental Conditions Driving Growth Speed
Temperature is the primary driver influencing St. Augustine grass growth speed. The grass thrives in warm temperatures, with optimal shoot growth occurring when air temperatures are consistently between 80°F and 95°F. Root growth is accelerated when soil temperatures are ideally between 75°F and 85°F.
Growth slows dramatically as temperatures drop, and the grass enters dormancy when soil temperatures fall consistently below 55°F. When this happens, the grass will turn brown and stop growing altogether. Sunlight is also a factor, as St. Augustine grass requires a minimum of four to six hours of direct sunlight daily for optimal growth and to prevent thinning, even though it is one of the most shade-tolerant warm-season grasses.
Consistent moisture is also necessary to sustain rapid growth, as the grass needs approximately one inch of water per week, either from rainfall or irrigation. When water is scarce, the grass will immediately conserve resources, effectively halting growth to survive the dry period. In well-drained, sandy soils, it may even require half an inch of water every three days during high heat to prevent drought stress.
Management Techniques Affecting Growth
The growth rate of St. Augustine grass can be controlled through homeowner maintenance practices. Nitrogen is the nutrient that most directly stimulates growth, producing a deeper green color and increasing the thickness of the turf. Applying between one and four pounds of actual nitrogen per 1,000 square feet annually, starting in spring and continuing through summer, will maintain a healthy growth rate. Over-applying nitrogen can result in excessive growth, leading to more maintenance and a higher risk of disease.
Mowing practices directly influence the plant’s energy output and growth habit. St. Augustine grass should be maintained at a height between two and four inches. Cutting the grass too short, known as scalping, stresses the plant by removing leaf surface area needed for photosynthesis, slowing both root and lateral growth. Maintaining a taller height encourages deeper root development and faster spreading.
During the peak growing season, the grass may need to be mowed once a week. This adheres to the “one-third rule,” which dictates that no more than one-third of the leaf blade should be removed in a single cutting.
Soil health supports efficient growth by making nutrients more accessible and allowing stolons to root easily. St. Augustine grass prefers a slightly acidic to neutral pH, ideally between 5.0 and 7.5. Aerating the soil periodically reduces compaction, which improves oxygen flow and allows the runners and roots to spread more quickly and effectively.