St. Augustine grass, a warm-season turfgrass popular across the Southern United States, requires a precise fertilization schedule to achieve a dense, vibrant lawn. The timing of nutrient application is the most important factor dictating the grass’s overall health, density, and color throughout its growing season. Correctly timed fertilization encourages robust root development and minimizes the risk of disease and weed competition. This approach ensures the grass utilizes nutrients efficiently only when it is actively growing.
The Critical Spring Application
The start of the fertilization calendar must align with the grass moving from winter dormancy into active growth. The most reliable indicator for the first application is the soil temperature, which should consistently remain above 65 degrees Fahrenheit. Applying fertilizer before this threshold is reached is inefficient because the grass’s root system is not yet ready to absorb the nutrients, which can then leach away or feed early-emerging weeds.
A common mistake is fertilizing too early based solely on air temperature. New, tender growth stimulated by early nitrogen can be severely damaged if a late frost occurs, compromising the lawn’s health for the rest of the season. The initial application should focus on a slow-release nitrogen product, which provides a steady supply of nutrients over several weeks. This slow-release form encourages controlled growth and helps prevent a sudden flush of top growth that could be susceptible to stress.
For the first application, a complete fertilizer with a balanced ratio, such as a 3-1-2 or 4-1-2 NPK ratio, is recommended unless a soil test indicates specific deficiencies. Apply approximately one pound of actual nitrogen per 1,000 square feet, using the slow-release formulation to maximize nutrient uptake efficiency. Waiting until the lawn has fully greened up, typically about two to three weeks after the first signs of active growth, ensures the turf can immediately utilize the applied nutrients.
Sustaining Growth Through Summer
The summer months require a steady maintenance program to support the turf through its peak growing season. St. Augustine grass benefits from subsequent nutrient applications every six to eight weeks, though this frequency can be extended to ten weeks when using slow-release formulations. This schedule ensures continuous access to the nitrogen needed for the grass’s characteristic lush, dark green color and dense growth habit.
Summer applications should continue the use of a nitrogen-heavy fertilizer, focusing on maintaining the half- to one-pound of actual nitrogen per 1,000 square feet rate. Careful timing is necessary to avoid plant injury during periods of environmental stress. Never apply fertilizer when the lawn is experiencing severe drought or during extreme heat waves, especially when temperatures consistently exceed 90 degrees Fahrenheit.
Fertilizing under these conditions can cause the grass to burn, as the salts in the fertilizer draw moisture away from the already stressed roots and leaves. For lawns on sandy soil, which are common in many St. Augustine regions, a mid-summer application of a fertilizer higher in potassium is beneficial. Potassium, the third number in the NPK ratio, helps enhance the turf’s disease resistance and improves its tolerance to heat and drought stress.
Adjusting the schedule for regional conditions is important; for instance, lawns growing on heavy clay soils may require fewer applications than those established on sandy profiles. Consistent monitoring for signs of nutrient deficiency, like a pale green or yellowing appearance, can signal the need for a liquid iron supplement between the main fertilizer treatments. This provides a quick color boost without forcing excessive vertical growth.
Preparing for Dormancy: Late Season Strategy
The final fertilization of the season is designed to prepare the St. Augustine grass for winter survival rather than to promote top growth. This late-season feeding should be timed approximately six to eight weeks before the average date of the first expected frost in the region. The goal is to encourage the storage of carbohydrates and strengthen the root system for the coming dormant period.
This application must involve a significant change in the fertilizer’s nutrient profile, moving away from high nitrogen content. The preferred product is a low-nitrogen, high-potassium formula, often represented by ratios like 5-10-10 or a simple 0-0-25 product focusing entirely on potassium. Potassium is directly involved in processes that improve the grass’s cold hardiness and resistance to winter-related diseases.
It is important to cease all nitrogen-heavy applications by early to mid-fall, typically by mid-September, to allow the grass to naturally slow its growth. Applying nitrogen too late encourages a final flush of new leaf growth that lacks the necessary toughness to withstand freezing temperatures. This tender growth is susceptible to winter damage, which can lead to significant dieback and a slower spring green-up the following year.