The ratings for every lawn fertilizer are classified as N-P-K numbers. These numbers will be found on the front of every bag and are labeled N for nitrogen, P for phosphate and K for potassium. Although there are many different types of N-P-K fertilizers for garden plants, flowers, shrubs and other plants, those that are rated best for lawns have specific N-P-K numbers to help lawns grow and keep lawns healthy.
Choose a lawn fertilizer with a ratio of 12-4-8 in N-P-K numbers, which are considered the ideal fertilizer rates for your lawn. In the real world, these ratings mean 3 parts Nitrogen to 1 part Phosphorus to 2 parts Potassium.
Rate every lawn fertilizer with this criteria in mind. Nitrogen gives your grass a nice healthy green color and aids in shoot development. Phosphorus encourages healthy and deep root development, while potassium gives your grass a strong immune system to prevent against disease.
Use an organic fertilizer on your lawn to minimize burning. However, most organic fertilizers have lower rated nitrogen amounts, so you may use much more of an organic type to get the 12 nitrogen rating that is needed for a green and healthy lawn.
Rates of spreading fertilizer are always based on the nitrogen content. For example, if a fertilizer calls for being spread at a rate of 3 lbs. per 1000 square feet, that figure is based on the total nitrogen count, or the "N" number of the rated fertilizer. A 12-4-8 lawn fertilizer means the fertilizer bag is filled with 12 percent nitrogen. Divide that how many types of fertilizer there are in each bag, 3, by the amount of nitrogen or 12 percent. This gives you the number 25. In this instance, you will need to spread 25 lbs. of 12-4-8 fertilizer on a 1,000 square foot lawn over the course of the year for optimum results.