Lawn Care
Step-by-Step Palmetto Grass Maintenance for Shade Lawns
Palmetto St. Augustine (Stenotaphrum secundatum 'Palmetto') is a proprietary cultivar engineered for superior shade tolerance, cold hardiness, and a finer leaf texture than standard Floratam or Raleigh varieties. While it thrives in filtered light where other warm-season grasses fail, its dense stolon network and broad leaf blades demand highly specific maintenance protocols. Mismanaging Palmetto grass—particularly through low mowing or improper nitrogen timing—rapidly triggers Take-All Root Rot (TARR) and chinch bug infestations.
This guide provides a precise, step-by-step maintenance framework for Palmetto grass, detailing exact chemical rates, mowing tolerances, and seasonal transitions to maintain a dense, dark emerald canopy.
Phase 1: Spring Green-Up & Pre-Emergent Defense (March - April)
The transition from winter dormancy to active spring growth is the most critical window for Palmetto grass. The primary objective is to prevent summer annual weeds without suffocating emerging stolons.
⚠ The 'Wait to Mow' Rule: Never scalp Palmetto grass in early spring. Unlike Bermuda grass, St. Augustine varieties do not recover well from severe vertical mowing or scalping. Wait until the lawn has been mowed twice at its normal height before applying any post-emergent herbicides to avoid chemical burn on tender new tissue.
Step-by-Step Spring Protocol
- Apply Pre-Emergent (Soil Temp 55°F): Apply Prodiamine 65 WDG at a rate of 0.23 oz per 1,000 sq. ft. This provides a 4-month barrier against crabgrass and goosegrass. Water in immediately with 0.25 inches of irrigation to activate the chemical barrier in the top inch of soil.
- Hold Nitrogen Application: Do not apply nitrogen at first sign of green-up. Palmetto grass is highly susceptible to Brown Patch (Rhizoctonia solani) during cool, damp spring nights. Wait until you have mowed the lawn twice and nighttime temperatures consistently exceed 65°F.
- First Nitrogen Feeding (Late April): Apply a slow-release fertilizer like Milorganite (5-2-0) at 15 lbs per 1,000 sq. ft., or a synthetic Lesco 24-2-11 at 4 lbs per 1,000 sq. ft. to deliver exactly 1 lb of nitrogen per 1,000 sq. ft.
Phase 2: Summer Peak Growth & Pest Defense (May - August)
During peak summer, Palmetto grass focuses on lateral stolon expansion. Maintenance shifts to moisture management, high-canopy mowing, and aggressive insect scouting.
Summer Mowing & Watering Matrix
| Metric | Full Sun Zones | Heavy Shade Zones |
|---|---|---|
| Mowing Height | 3.0 - 3.5 inches | 4.0 - 4.5 inches |
| Mowing Frequency | Every 5 - 7 days | Every 10 - 14 days |
| Weekly Water Volume | 1.0 - 1.5 inches | 0.5 - 0.75 inches |
| Blade Sharpening | Every 20 hours of use | Every 20 hours of use |
Pro Tip for Shade: Raising the mowing height to 4.5 inches in shaded areas increases the leaf surface area available for photosynthesis, compensating for the lack of direct sunlight. According to Texas A&M AgriLife Extension, maintaining this higher canopy is the single most effective cultural practice for sustaining St. Augustinegrass under tree canopies.
Chinch Bug Scouting & Treatment
Palmetto grass is a preferred host for the Southern Chinch Bug (Blissus insularis). Damage often mimics drought stress, appearing as yellowing halos that turn brown and die.
- The Coffee Can Test: Remove both ends of a metal coffee can, push it 2 inches into the soil at the edge of a damaged area, and fill it with water. Wait 5 minutes. If more than 4-5 chinch bugs float to the surface, treatment is required.
- Chemical Control: Apply BioAdvanced 24-Hr Grub and Pest Control (Lambda-cyhalothrin) or a systemic like Arena .5 G (Clothianidin). As of 2026, granular Arena applications cost approximately $85 per 50lb bag, covering roughly 10,000 sq. ft.
Phase 3: Fall Transition & Root Building (September - November)
As daylight hours shorten and soil temperatures drop below 70°F, Palmetto grass slows top growth and redirects energy to the root system. The goal is to harden the plant against winter kill without forcing tender new shoots that will be destroyed by the first frost.
💡 Fall Fertilizer Shift: Stop applying high-nitrogen fertilizers by September 1st. Switch to a potassium-heavy winterizer, such as Lesco 0-0-7 or a sulfate of potash application, applying 1 lb of K2O per 1,000 sq. ft. Potassium thickens cell walls, drastically improving the grass's cold tolerance and drought resistance.
Aeration and Soil Decompaction
If your Palmetto lawn experiences heavy foot traffic or clay soil compaction, early September is the window for core aeration. Use a plug aerator to pull 3-inch deep cores spaced 4 inches apart. Leave the plugs on the lawn to break down naturally, returning beneficial microbes to the thatch layer.
Phase 4: Winter Dormancy & Weed Control (December - February)
While the grass is dormant, winter annual weeds like henbit, chickweed, and annual bluegrass (Poa annua) will aggressively colonize bare spots.
Safe Post-Emergent Herbicide Selection
St. Augustinegrass is notoriously sensitive to many common broadleaf herbicides (like 2,4-D and Dicamba) which can cause severe stunting or root death.
- For Broadleaf Weeds: Use Celsius WG. As of early 2026, Celsius WG retail pricing has stabilized around $110 for a 10oz bottle, which treats up to 8 acres. It is exceptionally safe for Palmetto grass even during transition periods.
- For Poa Annua & Broadleaves: Atrazine (e.g., Hi-Yield Atrazine Weed Killer) is the traditional standard. However, you are strictly limited to two applications per calendar year. Never apply Atrazine when daytime temperatures exceed 85°F, as it becomes highly phytotoxic to St. Augustine roots.
Troubleshooting Edge Cases: Take-All Root Rot (TARR)
Take-All Root Rot (Gaeumannomyces graminis var. graminis) is the most devastating soil-borne disease affecting Palmetto grass. It manifests in spring and fall as irregular, yellowing patches that fail to respond to watering or fertilization. The roots will appear black and necrotic when pulled.
"TARR thrives in alkaline soils and heavy thatch. The most effective cultural control is lowering the soil pH. Topdressing affected areas with a 1-inch layer of acidic sphagnum peat moss has been proven to suppress the fungus by creating an unfavorable acidic microenvironment at the stolon level." - Clemson University HGIC
If cultural controls fail, initiate a preventative fungicide rotation using Heritage Action (Azoxystrobin) and Headway (Azoxystrobin + Propiconazole). Apply at 21-day intervals during peak infection windows (soil temps between 60°F and 80°F).
Iron Chlorosis in High pH Soils
If your Palmetto grass turns a pale, washed-out yellow despite adequate nitrogen, it is likely suffering from iron chlorosis induced by high soil pH locking up micronutrients. Apply a chelated iron product like Feature 6-0-0 or a liquid Ironite spray at a rate of 3 oz per gallon of water per 1,000 sq. ft. to force rapid greening within 48 hours without pushing excessive top growth.
