How to Make St. Augustine Grass Spread Quickly
St. Augustine grass (Stenotaphrum secundatum) spreads exclusively by above-ground stolons (horizontal runners) rather than by seed or underground rhizomes. This means that its rate of spread is directly tied to the health and vigor of those stolon runners. A St. Augustine lawn that is properly fertilized, mowed at the right height, watered correctly, and established in appropriate growing conditions will spread noticeably faster than one that is neglected or mis-managed.
Understand How St. Augustine Spreads
St. Augustine stolons grow horizontally across the soil surface, rooting at each node that makes firm contact with moist soil. Each rooted node becomes a new plant center that sends up leaf blades and eventually produces its own stolons. The speed of this process depends on:
- The vigor of the parent plant, which is determined by nutrition, water, and sunlight
- Soil-to-stolon contact at each node, which determines rooting success
- Temperature, since stolon growth accelerates above 80 degrees Fahrenheit and slows significantly below 60 degrees Fahrenheit
The practical implication is that you cannot make St. Augustine spread in winter or in cool weather regardless of how well you manage the other factors. Focus your improvement efforts on the peak growing season: late spring through summer.
Step 1: Fertilize to Drive Stolon Vigor
Stolon growth requires nitrogen. A nitrogen-deficient St. Augustine lawn produces pale, slow-growing stolons that root poorly and do not spread effectively. Fertilizing during the active growing season provides the metabolic fuel that stolon growth depends on.
Fertilizer timing for St. Augustine: Apply nitrogen fertilizer in late spring after dormancy break, again in early summer if needed, and once more in mid-summer for lawns in longer growing season climates. Do not fertilize in fall as St. Augustine approaches dormancy.
Nitrogen rate: 0.5 to 1 pound of actual nitrogen per 1,000 square feet per application. St. Augustine does not need the high nitrogen input that Bermuda requires; over-fertilizing drives excessive thatch buildup and disease susceptibility.
Recommended fertilizer: A slow-release nitrogen fertilizer (polymer-coated urea) reduces burn risk and provides steady feeding over 8 to 12 weeks. Milorganite (organic, slow-release) is also appropriate and carries a very low burn risk, which matters on a grass that is somewhat sensitive to fertilizer salt injury.
For St. Augustine-specific product guidance, the weed and feed section covers compatible products: best weed and feed for warm season grasses.
Step 2: Water Correctly to Support Rooting
Stolons root at nodes that maintain contact with moist soil. Dry soil prevents rooting and can cause stolon tips to desiccate. St. Augustine during active spread benefits from consistent soil moisture in the top 2 to 3 inches, where new stolon nodes are attempting to root.
Irrigation guidance: Apply 1 to 1.5 inches of water per week during active summer growth, either from rainfall or irrigation. In sandy soil, split this into two applications per week to keep the surface layer consistently moist without waterlogging.
Watch for wilt signals: St. Augustine shows wilt stress by folding its leaf blades lengthwise and taking on a blue-gray color. This signals immediate irrigation need. Allowing the lawn to reach this stress level slows stolon growth.
Step 3: Mow at the Correct Height
Mowing height directly affects stolon vigor. St. Augustine mowed too short removes the leaf blade area needed for photosynthesis, reducing the energy available for stolon growth. Mowing too tall in shaded areas allows the canopy to shade stolons from the light they need to produce healthy runner growth.
Standard mowing height: 3 to 4 inches in sun; 3.5 to 4 inches in partial shade.
Mowing frequency: Every 7 to 10 days during peak growth. Never remove more than one-third of the blade height in a single mowing.
Sharp blades matter: Dull mower blades tear grass rather than cutting it cleanly, creating ragged cuts that increase water loss and disease entry points. Sharpen mower blades at least twice per growing season.
Step 4: Prepare Bare Areas to Accept Stolons
Bare areas in a St. Augustine lawn establish stolons most successfully when the soil surface is loose enough for nodes to make firm contact and root. Compacted bare patches prevent rooting regardless of how vigorous the stolons are.
For bare areas smaller than 6 inches across: loosen the surface slightly with a hand rake, remove any dead thatch, and allow adjacent stolons to cross into the prepared area. Water the area daily until new growth is visible.
For bare areas larger than 6 inches: take sod plugs from a dense area of the existing lawn and plant them at 12-inch intervals across the bare patch, pressing each plug firmly into the soil. Water plugs daily for two weeks. The plugs will establish and their stolons will fill the gaps between them over the following growing season.
Step 5: Ensure Full Sun Coverage
Stolon growth is fastest in full sun. St. Augustine in deep shade produces fewer and weaker stolons and fills in much more slowly than the same grass in direct sun. If bare or thin areas in your lawn coincide with tree shade, addressing the shade condition (raising the canopy, selectively removing low branches) will have a more lasting effect on spread rate than any fertilizer or watering adjustment.
What Slows St. Augustine Spread
Several factors consistently slow St. Augustine stolon growth beyond the management issues already addressed:
Chinch bug damage: Chinch bugs (Blissus insularis) feed on St. Augustine stolons at the soil surface, causing yellowing patches that thin and spread. A slowing or stopping of spread in a previously vigorous lawn warrants inspection of the thatch layer for chinch bugs. Treatment with imidacloprid or bifenthrin applied at the label rate addresses active infestations.
Thatch buildup: A thick thatch layer above half an inch prevents stolon nodes from making soil contact and rooting. Annual dethatching or vertical mowing in spring restores the soil contact that spread requires.
Compaction: Heavily compacted soil in high-traffic areas prevents rooting of new stolon nodes. Core aeration in these areas improves the soil structure that allows stolons to root.