How to Calculate Lawn Fertilizer
An established lawn needs nitrogen to grow and and maintain its health. Located on bags or bottles of lawn fertilizer are three figures associated with the letters NPK. These stand for the percentage of nitrogen, phosphorous and potassium. Fertilizer high in phosphorus is effective for promoting newly planted lawn growth. If you have a damaged lawn, look for fertilizer high in potassium. Does this Spark an idea?
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Instructions
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Conduct a soil pH test on your yard. You can find a soil testing kit at a gardening supply store. Dig a hole and fill the sterile sample containers. Send to the address provided on the kit and wait for the results. Fertilize your yard according to the results. If your soil is too acidic, apply lime to bring the pH range down. Alkaline soil needs sulfur to get the soil back to a normal pH range.
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Find out the square footage of your yard. Measure the width and length then multiply the two numbers together to get the square footage. If your yard isn't a rectangle, measure your yard in sections and add the square footage of all sections together.
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Choose either organic fertilizer, chemical fertilizer, quick-release fertilizer or slow-release fertilizer. Organic fertilizers are better for your soil and won't burn plants; however, chemical fertilizers are fast-acting and can be found at most garden supply stores. Quick-release fertilizers promote rapid vegetation growth but must be applied more frequently than slow-release fertilizers.
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Pick a fertilizer that is right for your yard. Liquid fertilizer is optimal for small yards, while granular fertilizers allow you to see where you are spreading fertilizer.
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Look at the package or bottle of fertilizer for the percentage of nitrogen, phosphorus and potassium. Established lawns need fertilizer with a high amount of nitrogen and low amounts of phosphorus or potassium. For a healthy established yard, apply 1 lb. of nitrogen per 1,000 feet of yard space. Depending on the results of your soil testing kit, choose a fertilizer that amends the soil.
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Take the weight of the bag of fertilizer and multiply it with the percentage of nitrogen indicated on the bag. For example, if you have a 15.5-pound bag of 32-3-4 fertilizer that indicates it covers 5,000 square feet, multiply 15.5 by 0.32 (32 percent nitrogen). The total (about 5) is the number of pounds of nitrogen the fertilizer will supply to 5,000 square feet, or the correct ratio of 1 lb. per 1,000 square feet.
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Tips & Warnings
Follow the link in Resources to help you calculate how much fertilizer you need for your yard.
Avoid overfertilizing your yard. When in doubt, always use less fertilizer.
