Lawn Care Tips
When to Fertilize Your Lawn in South Louisiana
By Apex Grounds Co. · February 10, 2025 · 5 min read
Fertilize South Louisiana lawns starting in late March or April when soil temperatures reach 65°F, again in June and August for summer feeding, and lightly in September. Avoid winter fertilization entirely. Timing matters more than quantity — fertilizing at the wrong time wastes money and can damage your turf.
Why Timing Is Everything in South Louisiana
South Louisiana's nearly year-round growing season is both an advantage and a challenge for fertilization. Unlike northern states where the fertilization window is narrow and predictable, our warm climate means grass can show some growth almost any month of the year — but that doesn't mean it's ready to absorb fertilizer effectively year-round. The key trigger is soil temperature, not calendar date and not air temperature.
St. Augustine grass — the dominant turf across Tangipahoa, St. Tammany, and Livingston parishes — doesn't begin active root uptake until soil temps consistently hit 65°F at the 4-inch depth. In the Ponchatoula and Hammond area, that typically happens between late March and mid-April. Fertilizing before that threshold pushes weed growth and leaches nitrogen into waterways without feeding your grass. Your professional fertilization program should be soil-temp driven, not calendar driven.
The South Louisiana Fertilization Calendar
Follow this seasonal schedule for warm-season grasses in our region:
Spring (Late March – April): First Application
This is the most important application of the year. Use a balanced slow-release fertilizer once soil temperatures are confirmed at 65°F. A product like a 15-5-10 or 16-4-8 with slow-release nitrogen will feed the lawn for 6–8 weeks as growth kicks into gear. Apply at the rate recommended on the label — typically 1 pound of actual nitrogen per 1,000 square feet.
Summer (June and August): Maintenance Applications
Apply a second round of slow-release nitrogen in early June to support peak-season growth. A third application in August helps sustain the lawn through the final weeks of intense heat before fall arrives. During summer, prioritize slow-release formulations — quick-release nitrogen in the heat of a Louisiana July can burn turf and create excessive, weak growth prone to disease. Pair your fertilization program with consistent lawn maintenance for best results.
Early Fall (September): Light Recovery Application
September marks the transition period in South Louisiana. A light application of a low-nitrogen, high-potassium fertilizer in early September helps the grass recover from summer stress and builds root reserves. Potassium (the third number on the fertilizer label) improves cold tolerance and disease resistance, making it especially valuable going into fall.
Winter (October – February): Stop All Fertilization
Do not fertilize from October through February. The grass is slowing down, its ability to absorb and use nitrogen is limited, and pushing new growth in fall makes the turf vulnerable to cold snaps and fungal disease — particularly brown patch, which thrives in South Louisiana's fall weather pattern. Any nitrogen applied in this window is largely wasted and potentially harmful.
Slow-Release vs. Quick-Release Nitrogen
In South Louisiana's heat, slow-release nitrogen is almost always the better choice for lawn applications. Quick-release products deliver an immediate green-up but can burn the turf in temperatures above 90°F, contribute to thatch buildup, and require more frequent re-application. Slow-release products — sulfur-coated urea, polymer-coated urea, or organic-based blends — feed gradually over 6–10 weeks, reducing the risk of burn and providing more consistent nutrition.
A soil test, available through the LSU AgCenter, will tell you exactly what nutrients your soil is deficient in before you spend money on fertilizer. Many Tangipahoa Parish soils have adequate phosphorus but may benefit from additional potassium, iron, or pH adjustment. Don't guess — test.
Common Questions
When should I first fertilize my lawn in South Louisiana?
Apply your first fertilizer of the year in late March or April, once soil temperatures at the 4-inch depth have consistently reached 65°F. Fertilizing too early in February or early March, when the grass isn't actively growing, wastes product and can promote weed growth without benefiting your turf. A simple soil thermometer takes the guesswork out of timing.
Should I fertilize my Louisiana lawn in the fall?
A light fertilizer application in September is beneficial for South Louisiana lawns, helping grass recover from summer stress and build root reserves before the mild winter. However, avoid high-nitrogen fertilizers after September — pushing lush top growth going into cooler months makes the turf more vulnerable to cold damage and fungal diseases like brown patch, which is most active in fall.
What fertilizer is best for St. Augustine grass in Louisiana?
St. Augustine grass in South Louisiana responds well to a balanced fertilizer with a nitrogen-phosphorus-potassium ratio around 3-1-2 (such as a 15-5-10 or 16-4-8 formulation). For summer applications, choose a slow-release nitrogen source like sulfur-coated urea to feed the lawn gradually without the risk of burn during the heat. Have your soil tested to determine if you need phosphorus or potassium supplementation.
Can I over-fertilize my lawn in Louisiana?
Yes, over-fertilization is a common and damaging mistake in South Louisiana. Excess nitrogen pushes rapid, weak top growth that is highly susceptible to fungal diseases, particularly brown patch. It can also burn the turf during summer heat and contribute to thatch buildup that harbors pests. Follow package rate guidelines and never apply more than 1 pound of actual nitrogen per 1,000 square feet in a single application.