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Top 10 fertilizer tips from Hillsborough County Extension Service

Learn how to choose and apply fertilizer in accordance with the County's new ordinance

On Wednesday, Nov. 17, Hillsborough County commissioners approved an ordinance that limits fertilizer use during the rainy season from June 1 through Sept. 30, unless subject to an exemption, which includes agriculture. The ban includes the application of fertilizers containing nitrogen and phosphorus in unincorporated Hillsborough County. The goal of the new ordinance is to continue the County's mission of keeping contaminants out of local waters.

With the new ordinance, Hillsborough County Extension Service, which provides education and services in agriculture, lawn and garden, and professional horticulture services, has some helpful tips for homeowners on how to choose and apply fertilizer.

How to choose the right fertilizer:

  • The fertilizer ordinance applies to any product that contains nitrogen and/or phosphorous in the guaranteed analysis or on the label. Check labels carefully for things to avoid, such as systemic insecticides, fungicides, and some preemergent weed killers.
  • Look at fertilizer labels to determine the source of slow-release nitrogen or insoluble nitrogen, which must be at least 50 percent.
  • Choose a fertilizer with a 2:1 or 1:1 ratio of nitrogen (first number on the bag) and potassium (third number on the bag). Potassium is a key nutrient in keeping turfgrass healthy.
  • Choose a fertilizer with zero phosphorous (the second number on the bag) unless a soil test shows deficiency. Adding more phosphorous when there's enough in the soil can result in runoff, leaching, and wasted product.
  • Micronutrients such as manganese may be helpful. A soil fertility test plus micronutrients can provide information about the nutrient makeup of soil.

How to safely apply fertilizer:

  • Don't apply fertilizer before it rains. Most fertilizers only need to be watered in about ¼ inch to ½ inch, so putting fertilizer down before it rains can result in runoff and wasted product.
  • Don't apply fertilizer when turf is dormant in the winter, which can stress turf the following spring when it greens up.
  • Fertilize with a long-term controlled-release product at the end of May, ahead of the rainy season. The grass will receive low doses of nitrogen over a period of three to four months, depending on the product used.
  • When the rainy season is over, fertilize again with a product that has a more soluble nitrogen component, such as sulfur-coated urea. This will reduce the potential for the fertilizer to release nitrogen during the winter months when the ability to take up the nutrients is reduced.
  • Leave grass clippings on the lawn or blow them back into the landscape because they can add nutrients and replace a fertilizer application. Do not blow or direct them into roads, storm drains, or ditches, and keep a 10-foot fertilizer-free zone near water bodies.

If you have any questions regarding fertilizer use, visit or call (813) 744-5519. Residents are also invited to attend Extension Service's lawn and landscape classes.

Hillsborough County Extension Service is an educational service provided by University of Florida's Institute of Food and Agricultural Sciences (IFAS) and Hillsborough County. Extension offers education and information to Hillsborough County residents through workshops, publications, and other media.