It would be nice if plants received all the nutritional benefits they needed from the soil beneath them but this is seldom the case. Accordingly, most all plants can benefit from fertilizer as it enables them to reach their full potential in health, beauty, and bounty. Proper fertilization is not an art; it's a science. There's a lot to understand to fertilize correctly. Let’s explore some of the need-to-knows.

Fertilizer Basics: Understanding the Numbers

All fertilizers are labeled with a guaranteed analysis. Three numbers are prominently displayed on the bag. The first is the percentage of nitrogen by weight; the second is the percentage of phosphate and the third is the percentage of potassium. The only way to absolutely know what your soil needs it to have it tested to determine the level of these nutrients in the soil of your lawn. Most soils are generally rich in phosphate and so the second number on the bag should be lower than the other two, usually 0% to 3% (having said that, you may indeed have a phosphate deficient lawn that needs a lot more). As a general rule, the first number should be 1.5 to 3 times the third number. So you may be looking for an analysis such as 20-0-11 or a 29-3-12. You should avoid products like 13-13-13 or even the most common recommendation of 16-4 8 unless you have soil test results that recommends that much phosphate. In some states it is illegal to apply phosphate fertilizer without a soil test recommendation; so in these cases the middle number should be 0. Confused yet?  While hopefully this information is helpful, it also likely reinforces the importance of “getting it right” as your landscape relies heavily on the foundation of soil health.

The Complexities of Nitrogen 

Take a close look at the ingredients statement on a bag of fertilizer. It lists the sources of nitrogen nutrients the product contains. Words like nitrate, ammonium and urea indicate rapidly available nutrients that will create quick greening and growth. Sources such as sulfur or polymer coated urea, methylene urea, ureaformaldehyde and organics are slow release sources that last longer and green more slowly, but are less likely to damage grass if over-applied. The ingredient statement will also list the percentage of nitrogen that is slow release and the percentage that is rapidly available. If you are not experienced applying fertilizer you should purchase a product with 30% or more of the nitrogen in slow release forms, since you are less likely to burn your lawn if you make a mistake. Experienced professionals have a wider variety of options available to them as they are trained in the best product application for the job at hand.

The Right Amount of Fertilizer

Determining the right amount of fertilizer to apply will require a little math. Begin by measuring the average length and width of your front, side, and back lawns. The area of each is the average length times its average width. Add up the areas of the lawns on the various sides of your house to give the total square footage of your lawn.. Write that number down because it will be used every time you buy something for your lawn. Many fertilizer bags list the size of the lawn they will cover. To calculate the amount of lawn a bag will treat at 1 pound of N/1000 square feet multiply the percentage N times the total bag weight and divided by 100. As an example, a 25 pound bag of 29-0-12 fertilizer will treat 29 X 25 ÷ 100 = 7.25 thousand square feet.

There is no cookie-cutter approach for healthy plants. Each landscape is different and requires the right products to be applied, in the right amounts, at the right time of year to ensure good health. Fertilization is one example of the complexities required in the science of healthy landscapes. To eliminate guess work and to ensure you are obtaining the maximum environmental benefits of your landscape, have your lawn inspected and cared for by a professional.

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