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It's too late to fertilize grass now
Ask a master gardner
Robert Bell
Can I fertilize my lawn now?
No. The cooler nighttime temperatures we are experiencing is a signal for our warm season grasses to enter into their dormant period. Fertilizing now will promote continued growth, which will increase the risk of cold injury when our first frost occurs. Here’s what you need to know concerning fertilizing lawns:
A regular fertilization program is important to maintain healthy, attractive turf. It should include applying the correct type and amount of fertilizer at the right time. Proper fertilization is generally the most cost-effective practice to have a nice lawn. However, fertilization must be combined with proper mowing, watering and pest management for the best results. Each turf grass species has specific nutritional needs and a fertilization program should be based on soil test analysis.
Centipede has a natural light green color and is suited to acid soils (pH 5.0 to 6.0) but grows best at a higher pH. High rates of fertilizer, especially nitrogen, will produce a dark green color but will also lead to growth problems. One to two pounds of nitrogen per 1,000 square feet per year are generally good for centipede, although it will grow well without any fertilizer. The 2-pound rate may be preferable on sandy soils. Apply nitrogen in split applications. Apply the first two to three weeks after spring green-up and the second in midsummer (July-August). Determine phosphorus and potassium needs by soil testing. If soil testing is not used, a general purpose fertilizer with a 3-1-2  nitrogen-phosphorus-potassium (N-P2O5-K2O) ratio such as 12-4-8 is good. Apply 5 pounds of 12-4-8 per 1,000 square feet after spring green-up and again in midsummer. Another possible choice of fertilizer is four pounds of 16-4-8 per 1,000 square feet after spring green-up and in midsummer. Apply the fertilizer evenly over the area when the grass leaves are dry. Do not fertilize centipede after July.
St. Augustine grass is responsive to nitrogen fertilizer in terms of color and growth rate. St. Augustine grass requires about one pound of nitrogen per 1,000 square feet per month during the growing season to maintain satisfactory color and density.
At rates above 1 pound per 1,000 square feet, St. Augustine grass produces lush growth that is highly susceptible to insects and diseases. Thatch accumulation is also a problem when nitrogen fertilization exceeds the required rate.
A late summer fertilization of St. Augustine grass helps maintain color and density of the lawn into the winter and promotes early recovery of the grass in the spring. To extend the length of time a St. Augustine lawn is attractive, the lawn should receive about 1 pound of nitrogen every 30 to 60 days from early spring through Sept. 15. Do not fertilize after mid-September.
The first application of fertilizer to Bermuda grass should be made in spring when the grass is 50 percent green or when soil temperatures are above 65 degrees F. Fertilize Bermuda grass every six weeks thereafter until mid-September.
A “winterizer” fertilizer may be applied in mid-September but no later.
If soil testing is not used for St. Augustine and Bermuda, the complete fertilizer used can range from 16-4-8 to 10-10-10 and 5-10-15, etc. Most of the warm-season grasses require three to seven pounds of nitrogen per 1,000 square feet per year to remain hardy and attractive. This fertilizer is usually applied in three to five applications during the growing season. A typical example would be 10 pounds of 12-4-8 per 1,000 square feet in early spring when green-up begins, 10 more pounds in mid-summer, and six to eight weeks before the average first frost date (mid-September). This gives a total of 3.6 pounds of nitrogen.
For more information, contact your local county extension office. 
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