4Rs of Fertilizer Application
The old cliché is “April showers bring May flowers”, but April deluges create weak plants and yellow grass. You were following the UF/IFAS recommendations and waited until April 15th to fertilize. You followed the Urban Turf Rule and applied a low-phosphate fertilizer with slow-release nitrogen. Yet, your grass is yellow and the shrubs haven’t put on any new growth. What happened? The 18” + of rainfall that we experienced at the end of April flushed nearly everything out of the soil, including any fertilizer you applied. Nitrogen and potassium are highly leachable. Phosphorus is also depleted under saturated soil conditions.
If you haven’t submitted a soil test since the storm, now is the time to do so. It’s time to apply a summer fertilizer, but it needs to address all the nutrient deficiencies created from the excess rain. Soil test kits can be obtained from your County Extension office. When you get the results from the University of Florida Lab, it is important to remember the 4 Rs when applying fertilizer. It needs to be the Right Source, applied at the Right Rate, at the Right Time, and over the Right Place.
Best Management Practices (BMPs) have been developed to allow individuals to make conscientious decisions regarding fertilizer selection that will reduce the risk of water contamination. The Right Source for a BMP-compliant fertilizer is one that contains a portion of slow-release (water insoluble) nitrogen with little to no phosphorus, and a potassium level similar to the nitrogen percentage (e.g. 15-0-15, that contains 5% coated nitrogen). However, a soil test is the only way to accurately identify the specific nutrients your landscape is lacking. Many soil tests indicate a need for phosphate and currently it is illegal to apply more than 0.25 pounds per 1,000 sq. ft. without a soil test verifying the need.
Next, the fertilizer must be applied at the Right Rate. In order to do that, you must know the square footage of your property and how much you can spread using the settings on your equipment. Individuals walk at varied speeds and the product recommended rates are based on 1,000 sq.ft. areas. For information on calibrating application equipment refer to 
the publication, “How to Calibrate Your Fertilizer Spreader”. Using the 15-0-15 fertilizer mentioned earlier, the Right Rate for one application would be 3 pounds per 1,000 sq.ft.. That 35 pound bag is all that is needed for a nearly 12,000 sq.ft. yard (a large corner lot).
The Right Time for applying fertilizer is when the plants are actively growing and beginning to show nutrient deficiencies. Summer, when rainfall and irrigation is frequent, is often a typical application time. The Right Place is only on living plant areas. Be cautious to avoid getting fertilizer on the sidewalk, driveway and street. A deflector on your spreader is very helpful. Otherwise, be sure to sweep or blow the fertilizer back onto the grass or into the landscape beds. Avoid having fertilizer end up in any water body.