St. Augustine grass is a warm-season turf variety recognized for its dense, blue-green color and thick, broad blades. Its ability to tolerate heat and moderate shade makes it well-suited for the climate of Southern California, which features mild winters and long, dry summers. Proper fertilization timing is paramount for maintaining a healthy St. Augustine lawn, maximizing nutrient absorption and preventing waste. Aligning applications with the grass’s active growth phases promotes vigorous root development and a lush appearance.
Spring Awakening The First Application
The initial application of fertilizer should be timed by the soil temperature, not the calendar. St. Augustine grass begins its active growth cycle when the soil consistently reaches 65 to 70 degrees Fahrenheit. In Southern California, this occurs around late April or early May, after the risk of late-season frost has passed. Fertilizing too early encourages tender top growth vulnerable to cold snaps.
This first feed should utilize a lighter, balanced fertilizer blend, rather than a high-nitrogen product. The goal is to gently wake the turf and stimulate root growth before aggressive shoot development begins. A slow-release formula provides a steady nutrient supply without causing a sudden flush of growth, ensuring the grass establishes a strong foundation for the summer.
Summer Maintenance Mid-Season Feeding
Once the summer growing season is underway, St. Augustine grass requires regular feeding to manage heat and drought stress. Maintenance generally involves applications every six to eight weeks between June and August. This consistent nutrient supply supports the high metabolic demand of the grass during its peak growth period.
For summer applications, selecting a fertilizer with a high percentage of slow-release nitrogen is important. Slow-release nitrogen prevents “fertilizer burn,” which occurs when fast-release salts scorch the turf blades in extreme heat. Apply a nitrogen-rich formula at a rate of 0.5 to 1 pound of actual nitrogen per 1,000 square feet per application to maintain vibrant green color. Skip application if local temperatures exceed 95 degrees Fahrenheit, as the grass will be focused on survival.
Preparing for Dormancy The Final Feed
The final application prepares the St. Augustine lawn for cooler months and should occur in early fall, typically September or early October. In Southern California’s mild climate, the grass slows its growth significantly rather than entering full dormancy. This feed shifts focus from promoting top growth to enhancing below-ground root development and carbohydrate storage.
Fall fertilizers should contain moderate to low nitrogen levels to avoid stimulating new leaf growth vulnerable to cold. A blend with a higher proportion of potassium is beneficial, as potassium strengthens cell walls and enhances resilience. Applying heavy nitrogen fertilizer past mid-fall can increase susceptibility to fungal diseases like Brown Patch, which thrive in cooler, moist conditions.
Selecting the Right Fertilizer Blend
When selecting a product, the NPK ratio (Nitrogen, Phosphorus, and Potassium) is the most important factor. St. Augustine grass performs best with a fertilizer ratio favoring nitrogen, such as 4-1-2 or 3-1-2, often seen in blends like 16-4-8 or 20-5-10. Since many Southern California soils already have adequate phosphorus, using a low or zero-phosphorus blend helps prevent nutrient runoff.
The majority of the nitrogen should be in a slow-release form, ensuring gradual, consistent feeding over several weeks. This steady release reduces the risk of nutrient leaching, a concern where deep, infrequent watering is recommended. Look for formulations that contain micronutrients, particularly iron, as it enhances deep green color without forcing excessive vertical growth.