How to Get St. Augustine Grass to Spread and Fill Bare Spots

At TurnKey Lawn Care, lawn repair and feeding are part of the care we provide across the metro. If a bare area won’t fill in, request a free estimate and we’ll work out what’s stopping it.

This guide explains how St. Augustine spreads, the common reasons it stops, and the mowing, feeding, watering and planting steps that get runners moving into thin and bare areas again.

How St. Augustine spreads

Why St. Augustine stops spreading

When runners won’t move into an area, one of a few problems is usually at work:

• Shade. LSU notes St. Augustine tolerates moderate shade but performs best in full sun, and runners slow down in deep shade
• Compacted soil. Runners can’t root easily into ground that’s packed hard by foot traffic
• Mowing too short. Scalped grass has less leaf to fuel new growth
• Low fertility. An underfed lawn grows slowly and spreads slowly
• Ongoing damage. Chinch bugs, disease or standing water keep killing what the runners try to fill
• Edging and trimming. Runners reaching into bare spots get cut back before they can root

An LSU AgCenter article on lawn repair makes the same point about patching: identify what caused the grass to die and fix the problem, whether that was traffic, heavy shade, low or wet spots, freeze, insects, disease or a spill.

Step 1: Mow at the right height

LSU recommends mowing St. Augustine at 2.5 to 3 inches through the growing season, and never removing more than one-third of the leaf blade at one mowing. Leaf area feeds the plant. A lawn kept at the upper end of that range has more energy to push runners outward than one cut short every week. Our page on how short to cut St. Augustine explains why height matters so much for this grass in particular.

Step 2: Feed it correctly

St. Augustine needs nitrogen to grow and spread, but more isn’t always better. LSU recommends up to 3 pounds of nitrogen per 1,000 square feet per year, and never more than 1 pound per 1,000 square feet in a single application. Timing matters as much as the amount. Feeding while the grass is actively growing, in spring and summer, supports runner growth. Heavy nitrogen late in the year can do more harm than good, since it pushes soft growth going into the cooler, disease-prone months. Soil pH plays a part too. LSU notes St. Augustine prefers soil that’s very slightly acidic to neutral, ideally around pH 6.5. A soil test tells you where your lawn stands. Our guide to the best fertilizer for St. Augustine covers product choice and timing.

Step 3: Water deeply, not constantly

Runners need moisture to root at their nodes, especially where they’re reaching into bare soil. Deep, occasional watering that accounts for rain supports rooting without keeping the lawn soggy. Constant shallow watering does the opposite. It keeps roots near the surface and raises the risk of fungal problems in St. Augustine. Our Louisiana lawn watering schedule gives a practical routine. Pay extra attention to the bare area itself. The soil there dries out faster than under dense turf, so an occasional hand-watering helps runners that are trying to root into it.

Step 4: Loosen compacted spots

Bare patches along paths, by gates and near steps are often compacted from foot traffic. Runners can grow across hard, packed soil, but they struggle to root into it. Loosening the top of the bare area with a garden fork or aerating it while the grass is actively growing gives the runners soft soil to root into. Adding a thin layer of compost or topsoil over hard ground can help too. If the area is a shortcut people use every day, a stepping-stone path may work better than grass. St. Augustine won’t hold up to constant traffic in the same spot.

Step 5: Plant plugs or sod in larger gaps

Small bare spots usually fill in from the edges once growing conditions improve. Larger areas close much faster with help. LSU notes that St. Augustine can be established from plugs or sod, and that no commercial St. Augustine seed is currently available in Louisiana. That rules out overseeding as a fix, which surprises many homeowners.

Option	Best for	What to expect
Let runners spread	Small bare spots in a healthy lawn	Slowest, no cost beyond good care
Plugs about 1 foot apart	Medium thin or bare areas	Fills in over the growing season as plugs spread
Sod	Large bare areas or high-visibility spots	Covered immediately, then roots in over several weeks

LSU recommends planting plugs about 1 foot apart. Plant them level with the surrounding soil, water them in well and keep them moist while they root. For sod patches, the LSU repair article recommends cutting a straight-edged area, removing dead roots and debris, loosening the soil, and laying pieces tightly together before pressing them firmly into the soil.

Step 6: Let the runners do their job

Once runners start moving, protect them. Edging and string-trimming often cut off the very runners that are trying to fill a bare spot, especially along beds and walks.

• Hold off on edging the bare area until runners have rooted into it
• Keep foot traffic off the patch while runners are establishing
• Avoid herbicides on or near the bare area while it’s filling in
• Keep feeding and watering the healthy grass at the edge, since that’s where new runners come from

Spreading in shade

Shade is the most common reason St. Augustine won’t fill in under live oaks and along the north side of a house. LSU describes St. Augustine as having greater shade tolerance than other warm-season grasses and able to handle moderate shade, while performing best in full sun. In moderate shade, raising the mower to the top of the range and easing off nitrogen helps the grass make the most of limited light. In deep shade, it may never fill in fully no matter what you do. Thinning tree canopies to let in more light can help, and in the deepest shade a ground cover may be the better choice. Our guide to the best ground cover for shady yards covers alternatives, and our post on plants under live oaks looks at options for heavily shaded New Orleans yards.

Mistakes that slow the spread

Several common habits work against a lawn that’s trying to fill in. Most are easy to change once you know about them:

• Scalping the lawn before summer to make it look tidy, which strips the leaf the runners depend on
• Spreading heavy fertilizer all at once, beyond LSU’s 1 pound of nitrogen per 1,000 square feet per application
• Running sprinklers every evening, which keeps the surface wet and invites disease
• Edging hard along every bed and walk, trimming off runners before they can root
• Planting plugs or sod into the same compacted, shaded or waterlogged spot that killed the grass before

Correcting even two or three of these usually makes a visible difference within a single growing season. The healthy grass at the edge of the bare area is doing the work, so anything that strengthens it speeds up the repair.

How long it takes

St. Augustine spreads fastest in the heat of the growing season, from late spring through summer. A bare spot addressed in spring can close a good deal by fall, while one tackled in October will mostly wait until the following spring. Plan repairs for when the grass is actively growing, and give them a full season before judging the result. Our St. Augustine grass care guide covers the seasonal routine that keeps a lawn dense enough to fill its own gaps.

Frequently asked questions