When should I fertilize?
Don’t jump the gun and fertilize the lawn too early. Mid April is the target date to apply the first fertilizer application to warm season lawns in north Florida.
What fertilizer should I use?
Find a fertilizer that has a 2:1 or 1:1 ratio of nitrogen to potassium, which represents the first and third numbers on the bag. The middle number, phosphorous, should be 2 or less. Examples include 15-2-15, 16-2-8, etc. This represents the percentage of nitrogen, phosphorous and potassium based on a one hundred pound bag. A 100 pound bag of 15-2-15 fertilizer contains 15 pounds of nitrogen, 2 pounds of phosphoric acid, and 15 pounds of potash. A 50 pound bag of the same analysis contains 7.5 pounds of nitrogen and potash and 1 pound of phosphoric acid.
Next, look at the nitrogen source
Find a fertilizer that has 30% or more of the nitrogen in a controlled release (water insoluble) form. To calculate the percentage of slow release nitrogen in a fertilizer, take the number listed for slow release, divide by the first number on the fertilizer bag (total nitrogen) and multiply by 100. For example, if a 15-0-15 has 7% water insoluble nitrogen, divide 7 by 15 and multiply by 100 to get 46.67%.
Then look at secondary plant nutrients and micronutrients
For lawns, iron and manganese are the most important, especially in soils with a pH over 6.5. “Weed and Feed” type fertilizers are not the best product to apply at this time. It’s a timing issue. The herbicide is traditionally a pre-emergence herbicide which should have been applied earlier (mid February to March 1), when weeds were germinating, to be effective. That is not the right time to fertilize because lawns are dormant.
How Much Fertilizer to Purchase and Apply?
Only buy what you need for one application or at least this growing season because fertilizers do not store well. First, determine the overall square feet of lawn area by dividing the lawn into rectangles. Multiply the length by the width (60’ x 30’ = 1,800 sq. ft.) of each rectangle. For triangles use the formula area = 0.5 x base x height 0.5 x 40’ x 80’ = 1,600 sq. ft. Add these together to get the total square feet of fertilized area.
Another option is to look at the total area of your property
Then subtract the area for the house, deck, driveway, sidewalks, and garden area (all non-fertilized areas) to get the total yard area. Once you have the square feet and know the fertilizer analysis, calculate how much fertilizer to purchase. If the fertilizer has 30% or more water insoluble nitrogen, apply at a rate of 1 pound of nitrogen per 1,000 square feet. A 50 pound bag of 15-2-15 with 30% or more water insoluble nitrogen will cover 8,000 square feet. If less than 30% water insoluble nitrogen, apply 0.5 pound nitrogen per 1,000 square feet. A 50 pound bag of this type fertilizer (15-2-15) will cover 16,000 square feet.
The fertilizer bag will state how many square feet can be covered based on the analysis. Another option is to use the University of Florida publication ‘Homeowner Best Management Practices for the Home Lawn’ at https://edis.ifas.ufl.edu/publication/ep236. This includes a table that gives the pounds of fertilizer to apply based on nitrogen content and square feet of lawn area.
How often should I fertilize?
Know what type of lawn is in your landscape. The number of pounds nitrogen per 1000 square feet per year in north Florida based on lawn type is as follows: 2 to 3 for bahiagrass, 3 to 5 for bermudagrass, 1 to 2 for centipedegrass, 2 to 4 for St. Augustinegrass, and 2 to 3 for zoysiagrass. Notice there is a range. Lower amounts of nitrogen are for lower maintenance lawns versus larger amounts are for a higher maintenance lawn. For lawns that require two pounds of nitrogen per 1,000 square feet per year, the most critical application times are mid-April (at the beginning of the growing season) and September (going into the winter).
Are there other fertilizer tips?
Do not apply fertilizer prior to a heavy rain. Much of the fertilizer will be lost due to runoff or leaching if a heavy rain occurs within 8 to 12 hours of a quick release urea application. Lightly water-in fertilizer with one-quarter inch of water to prevent nitrogen loss and burning the grass. Do not apply fertilizer within ten feet of a body of water unless using a spreader with a deflector shield. If using a deflector shield, stay three feet away from water. Keep fertilizers on lawn areas and avoid application to hard surfaces like sidewalks, driveways and roads. If fertilizer is accidentally applied to hard surfaces, blow or sweep material onto the lawn or put it back in the bag.
For more Florida-Friendly tips on managing lawns, go to https://edis.ifas.ufl.edu/publication/ep236
Article written by Terry DelValle Extension Agent, April 2023
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