If you’re planning a lawn with St. Augustine grass, one of your first questions is probably, how tall does St Augustine grass grow? Understanding its maximum height and spread is key to keeping it healthy and looking its best. This grass is a popular choice in warm climates for good reason, but it does have specific needs.
Let’s look at what you can expect from this thick, carpet-like grass and how to manage its growth effectively.
How Tall Does St Augustine Grass Grow
St. Augustine grass has a distinct growth habit. It doesn’t grow tall and upright like some other grasses. Instead, it spreads horizontally using above-ground runners called stolons. These stolons creep along the soil, rooting at the nodes and creating a dense mat.
In terms of vertical height, here’s the typical range:
- Optimal Mowing Height: Most experts recommend maintaining St. Augustine at a height of 2.5 to 4 inches.
- Maximum Unmowed Height: If left completely uncut, St. Augustine grass can reach a height of 6 to 12 inches. It will eventually flop over under its own weight, creating a messy, uneven appearance.
- Spread: The stolons can spread several feet in a single growing season, quickly filling in bare spots and creating a solid turf.
Why Mowing Height is So Important
Cutting St. Augustine too short is one of the biggest mistakes you can make. This is called “scalping.” It stresses the grass, making it vulnerable.
- Weed Invasion: Short grass allows sunlight to reach weed seeds, encouraging them to sprout.
- Root Damage: The grass focuses energy on regrowing blades instead of maintaining deep, healthy roots.
- Pest and Disease: Stressed grass is more suseptible to chinch bugs, fungal diseases, and heat damage.
Keeping it at 3-4 inches provides shade for the soil, conserves moisture, and promotes a robust root system that can handle drought better.
Factors That Influence Growth Rate and Height
Several things affect how fast and how tall your St. Augustine grass will grow.
Climate and Season
St. Augustine thrives in warm, humid climates (USDA zones 8-11). Its peak growth occurs in the hot summer months. Growth slows significantly in late fall and winter, often going dormant and turning brown after the first hard frost.
Sunlight Exposure
This grass prefers full sun but can tolerate some shade. However, in deep shade, it will grow more slowly, become thin, and may struggle to spread. It will often stretch taller in shade as it reaches for light, but this growth is weak.
Soil and Nutrition
Rich, well-draining soil is ideal. Regular feeding during the growing season with a nitrogen-rich fertilizer promotes vigorous growth. A soil test can tell you exactly what nutrients your lawn needs, preventing guesswork.
Watering Practices
Deep, infrequent watering is best. This encourages roots to grow downward. Frequent, shallow watering leads to shallow roots and can sometimes encourage faster top growth without the strong foundation.
Step-by-Step Guide to Managing Height and Spread
Proper management keeps your lawn from becoming overgrown and maintains its health.
1. Mowing Correctly
Set your mower blade high. Never remove more than one-third of the grass blade in a single mowing. If the grass has gotten too tall, gradually lower the height over several mowings to avoid shocking it.
Keep your mower blades sharp. Dull blades tear the grass, creating brown tips and open wounds for disease.
2. Controlling Lateral Spread
St. Augustine’s stolons will spread into garden beds, over sidewalks, and onto patios. You have two main options for control:
- Edging: Use a manual half-moon edger or a power edger to create a clean, vertical barrier along hardscapes.
- Root Barriers: Installing a physical barrier in the soil along garden beds can help, but stolons can sometimes go over the top if the soil level rises.
3. Thinning and Dethatching
Over time, a thick thatch layer (a mat of dead stems and roots) can build up. If it gets over half an inch thick, it prevents water and nutrients from reaching the soil. You may need to dethatch using a specialized rake or machine.
4. Renovation and Repair
To fill in bare areas, you can use plugs or pieces of sod. Simply cut small squares from a healthy area of your lawn or buy plugs. Plant them 12-24 inches apart in prepared soil, and they will spread to fill the space within one to two growing seasons.
Common Problems Related to Growth
Sometimes, growth patterns can signal an issue.
- Thin, Sparse Growth: Often caused by too much shade, compacted soil, or nutrient deficiency.
- Rapid, Weak Growth: Can be a sign of over-fertilizing with nitrogen, especially if you are applying too much.
- Failure to Spread: If stolons aren’t creeping, check for soil compaction, pest damage (like grubs eating the roots), or extreme drought.
Comparing to Other Warm-Season Grasses
It’s useful to see how St. Augustine stacks up.
- Bermuda Grass: Has a lower optimal mowing height (1-2 inches) and spreads by both stolons and underground rhizomes. It’s more tolerant of short mowing.
- Zoysia Grass: Grows more slowly and denser, with a recommended height of 1-2.5 inches. It’s generally more drought-tolerant once established.
- Centipede Grass: Known as a low-maintenance grass, it grows slower and prefers a height of 1.5-2.5 inches. It requires less fertilizer than St. Augustine.
FAQ Section
How fast does St. Augustine grass spread?
Under ideal conditions (warm, moist, fertile soil), St. Augustine plugs can spread to cover an area within one to two growing seasons. Its stolons can grow several inches to a foot in length during the peak summer months.
Can you stop St. Augustine grass from spreading?
You cannot stop its natural spreading habit, but you can manage it. Regular edging along sidewalks and driveways is the most effective method. Installing deep physical barriers can also help contain it in planting beds.
What is the best height to cut St. Augustine grass?
The best height is between 3 and 4 inches during the growing season. In partial shade, keep it at the taller end of this range (4 inches) to help it capture more sunlight.
Does St. Augustine grass grow tall if not cut?
Yes, if left completely uncut, it can grow 6 to 12 inches tall. The blades will eventually bend over and layer on top of eachother, creating a thick, spongy mat that is prone to disease and pests.
Why is my St. Augustine grass not growing tall or spreading?
Several factors could be at play: insufficient water, poor soil nutrition, compacted soil, insect damage (check for chinch bugs or grubs), excessive thatch, or too much shade. A soil test is a great first step to diagnose the problem.
Knowing how tall St. Augustine grass grows and how it spreads gives you the tools to manage a beautiful lawn. Remember, the secret isn’t in letting it grow wild, but in maintaining that ideal 3-4 inch height. This practice encourages deep roots, shades out weeds, and results in a lush, durable turf that can handle the heat. With consistent mowing, feeding, and watering, your St. Augustine lawn will be the envy of the neighborhood for years to come.