How do I know how much fertilizer to apply?
The suggested rate per application is about one pound of actual nitrogen per 1,000 square feet of lawn. If fertilizers were 100 percent nitrogen, which they are not, it would take a pound of fertilizer to apply this rate. Divide 100 by the percent nitrogen in the bag (first number expressed a whole number) to figure how much is needed per 1,000 square feet. For example, a fertilizer with 20 per- cent nitrogen would require 100/20 or 5 pounds of fertilizer product per every 1,000 square feet of lawn.
The next figure needed is the total area or square footage of the lawn. Take your total lot size and subtract everything not in lawn to determine this figure. An acre is 43,560 square feet, if you know your lot expressed in a portion of an acre. Then subtract the square footage of the house, drive- way, gardens, patio, etc. The other way to figure is just to measure dimensions of the lawn areas and calculate as square feet.
Once you arrive at the square footage in lawn, divide this by 1,000. Then multiply by the pounds of fertilizer needed per 1,000 square feet figured above. This gives you the approximate pounds of fertilizer needed to spread on your lawn.
Using the previous example of a 20 percent nitrogen fertilizer, let’s walk through this. Dividing 100 by 20 gives 5, meaning 5 pounds of fertilizer is needed to supply 1 pound of actual nitrogen for every 1,000 square feet. If the lawn measures out to 12,000 square feet, dividing 12,000 by 1000 gives 12. Now take 5 times 12, which equals 60. This means it would take 60 pounds of fertilizer, spread over the 12,000 square foot lawn, to supply a rate of 1 pound of actual nitrogen per 1,000 square feet.