How to read a fertilizer bag and choose a fertilizer


Narrator: One of the most important pieces of information to find on a fertilizer bag is the amount of “slow-release” nitrogen in the fertilizer. “Slow release” means that nitrogen is available to the lawn over an extended time providing a steady supply of nutrition throughout the growing season. It’s a good idea to look for fertilizer with higher amounts of slow-release nitrogen. Look for the “slow release” percentage of nitrogen at the bottom of the “Guaranteed Analysis” section on the back of the bag. For example, this bag contains slowly available nitrogen from coated urea. You might also see the words timed-release, controlled-release or water insoluble nitrogen. Fertilizer with slow-release nitrogen will take a bit longer to show the effects but will last longer too — up to 60 days. But just because it lasts 60 days doesn’t mean you need to fertilize that often. In fact, you should only fertilize when your grass is actively growing. If you’re applying a fertilizer with 30% or more of slow-release nitrogen, then no matter what kind of grass you have or where in the state you live, apply no more than 1 pound of nitrogen for every 1000 square feet of lawn each time you apply fertilizer. To determine the correct amount of fertilizer per 1,000 square feet, divide 100 by the percentage of nitrogen in the bag. For example, a fertilizer with a 15-0-15 label contains 15% nitrogen, 0% phosphorus and 15% potassium. Divide 100 by 15 to get 6.6; this is the number of pounds of slow-release fertilizer needed to apply one pound of nitrogen per 1,000 square feet. This works for any fertilizer product or amount of nitrogen. Now let’s look at the three numbers on the front of the bag. These numbers indicate the percentage of the three prime elements needed for growth – nitrogen (N), phosphorus (P) and potassium (K). If you did a soil test, you’ll be able to refer to it now as you choose a fertilizer. The first number is for Nitrogen or the letter N. Nitrogen is responsible for rich, lush growth and a healthy, dark, green color. Too much nitrogen can make grass blades grow too fast, which can make your turf vulnerable to disease and drought stress. Plus, you’ll have to mow more often. The middle is Phosphorus or the letter P. Phosphorus is important for root growth. However, in most Florida soils, there is already a lot of phosphorus. That means we have to make sure the fertilizer we choose is very low in phosphorus. It is best to look for a fertilizer with low or zero P unless you have a soil test report that recommends adding phosphorus. The third number is for Potassium or the letter K. Potassium promotes strong stems and roots and helps move water within the plant. It improves disease resistance and prepares the grass to survive the cooler months. It’s best to look for a fertilizer where the first and third numbers are equal or in a ratio of 2:1. For more information on Florida-Friendly Fertilizing, contact your county UF/IFAS Extension office. You can also learn more online at WaterMatters.org/fertilizing. Brought to you by the Southwest Florida Water Management District.

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