St. Augustine grass is a warm-season turfgrass valued across Florida for its dense, carpet-like growth and rich color. Maintaining this lawn requires more than just regular watering and mowing; fertilizer timing is a major factor in its long-term health. Because St. Augustine grass is a vigorous grower, it requires a steady supply of nutrients throughout the active season to thrive in the state’s demanding climate. Proper fertilization timing ensures the grass can absorb nutrients when its root system is active, preventing waste and supporting resilient turf.
Identifying the Optimal Spring Start Time
The first fertilizer application of the year should be timed by the soil temperature and the grass’s biological signals, not the calendar. St. Augustine grass will not efficiently absorb nutrients until the soil temperature, measured at a four-inch depth, consistently reaches 65°F to 70°F. Applying a nitrogen-heavy fertilizer before this threshold is reached is ineffective, as the grass is still in its cool-season dormancy or semi-dormancy phase.
This critical temperature window usually coincides with the “green-up” phase, when the grass emerges from its winter color and begins active shoot growth. In North Florida, this may not occur until mid-to-late April, while in South Florida, it can happen as early as March. It is recommended to wait about two weeks after the turf has fully greened up before applying the first dose of nitrogen. Fertilizing too early can encourage tender new growth vulnerable to damage from a late-season frost, which is a risk in Central and North Florida.
The initial spring feeding should be a balanced or nitrogen-focused, slow-release product to jumpstart growth as the root system becomes active. A common application rate is between one-half to one pound of actual nitrogen per 1,000 square feet. This measured approach establishes a strong foundation for the intense growth period ahead and ensures the grass has the energy to outcompete emerging weeds.
Maintaining Growth During Peak Summer
The period from late spring through early fall constitutes the primary growing season for St. Augustine grass in Florida. During this time, the grass actively produces the dense stolons that create its thick turf. Fertilization intervals are typically scheduled every six to eight weeks to maintain vigor, though local ordinances heavily influence this timing.
Summer applications should prioritize slow-release nitrogen sources to provide a steady nutrient supply without causing excessive, weak top growth. Quick-release fertilizers can lead to a surge in growth that quickly burns out under intense summer heat or makes the grass more susceptible to disease. A high-potassium fertilizer, such as a 15-0-15 analysis, is recommended during the mid-summer months. Potassium helps the grass manage stress from heat and drought, enhancing its natural defense against common fungal diseases.
Nutrients, particularly nitrogen, can leach out of the sandy Florida soils more quickly. Adjusting the application rate to slightly lower amounts, often referred to as “spoon-feeding,” helps prevent runoff and ensures consistent feeding. Iron supplements can also be used between fertilizer applications to promote a deep green color without stimulating rapid growth.
The Final Fall Application
The final fertilization of the year prepares the St. Augustine grass for the cooler winter months. This application is ideally timed for late September or early October, giving the grass enough time to absorb the nutrients before temperatures consistently drop. The goal is to support root development and carbohydrate storage for winter survival, not to encourage new leaf growth.
The nutrient composition must shift away from high nitrogen to one that is rich in potassium. Potassium is essential for improving the grass’s cold tolerance. Applying a potassium-heavy blend, sometimes alongside phosphorus if a soil test recommends it, strengthens the root system and prepares the turf for its upcoming dormancy.
Applying nitrogen too late in the fall, particularly after mid-October, is counterproductive and can be damaging. Late nitrogen promotes soft, vulnerable growth that is easily damaged by the first frost. The final application ensures the grass has stored the maximum energy reserve to sustain it until the spring green-up.
Timing Restrictions and Local Ordinances
Fertilization schedules in Florida must comply with local ordinances designed to protect water quality. Many counties enforce a “blackout” period that typically runs from June 1st through September 30th, coinciding with the state’s heaviest rainy season. During this time, heavy, frequent rainfall increases the risk of nutrient runoff into storm drains and waterways.
These regulations prohibit the application of any fertilizer containing nitrogen or phosphorus during the blackout window. However, the use of fertilizers containing only potassium and other micronutrients, such as iron, is permitted. Homeowners must also adhere to setback requirements, avoiding fertilizer application within 10 to 15 feet of any water body, including lakes, ponds, and wetlands.
Beyond regulatory blackouts, avoid fertilizing St. Augustine grass when it is dormant or under stress, such as during a drought. The turf cannot utilize the nutrients effectively when its metabolism is shut down. Always check the specific ordinance for your county or municipality, as the exact dates and rules can vary across Florida.