A Crash Course in Fertilizer for Your Lawn

May 12, 2022

As the growing season speeds up, the home gardener looks at enhancing their yard and in particular, their lawn. In many cases, the lawn ranks as the principal feature of their yard. Things start to green up and one immediate response is to make it happen faster and apply fertilizer. However, there’s a few important things to know before making that trip to your local garden center or nursery.

First, have your soil tested. For a listing of soil testing labs in Illinois, a list is provided under the University of Illinois Extension at web.extension.illinois.edu. Phone numbers are listed that you can call for current fees and services. Some labs will provide sample bags prior to you taking a sample. You may find that your soil doesn’t need a fertilizer or that just by adjusting your soil pH level, your grass can take advantage of the nutrients that are already there in your soil.

Second, know what kind of grass you have in your lawn, whether it is a cool-season lawn or a warm-season lawn. Cool-season lawns, that have grasses such as Kentucky bluegrass or any of the fescues, are best fertilized in late fall, although they can be fertilized after the spring rains or early fall. Fertilizing too early brings lush growth requiring extra mowing and sometimes fungal diseases. Warm-season lawns with grasses such as Bermudagrass, buffalo grass or zoysia grass, are best fertilized with light applications through the growing season but the most important time being in the early spring.

Third, use only slow-release fertilizers. These fertilizers release nitrogen over a longer period so they don’t have to be applied as often and they are less likely to burn or be washed away when it rains. Good slow-release options include compost or well-rotted manure. Although, one excellent natural source is just to let your grass clippings lie. Grass clippings are an excellent source of nitrogen. While you don’t want large clumps on your lawn which can increase heat buildup, clippings from regular mowing will recycle important nutrients back into your soil. Save yourself the trouble of raking and bagging.

Fourth, know how to read the fertilizer label. Fertilizers are made up of three basic nutrients–nitrogen (N), phosphorus (P) and potassium (K), as well as several micronutrients. A bag of fertilizer with a label 10-10-10 means that the bag contains 10 percent nitrogen, 10 percent phosphate and 10 percent potash (fertilizer potassium). Nitrogen (N) gives the lawn its green color (the formation of chlorophyll), but keep in mind, it promotes leaf growth over root growth. If you choose to use a quick-release nitrogen fertilizer instead of a slow-release fertilizer, the result may end in fertilizer burn to your turf because the minerals are already in a salt form that pull the water out of your grass. The rule of thumb to reduce burn potential is to apply no more than 1 pound of actual nitrogen per 1,000 square feet of application.

Phosphorus (P) is important for root growth. New lawns require phosphorus in higher amounts than older, established lawns. However, if the pH of your soil is too high or too low, these levels may make phosphorus intake unavailable to your grass. The best pH range is between 6.0 and 7.0 or slightly acid.

Potassium (K) helps your lawn tolerate stress, disease, and insect damage. With most soil, except for sandy soil, potassium is usually already available, except if you have a very low pH.

Secondary nutrients and micronutrients are also necessary for turf growth, but quantities required are quite small. Fortunately, these are already found in most Illinois soils. They include sulfur and iron, and less common manganese, zinc or copper.

Keep in mind, that unless your soil is completely sterile, the recommended rates of fertilizer application are usually higher than what you really need and people tend to apply more than necessary based on the mistaken premise, “If a little does a lot of good, then a whole lot more does even better.” Fertilizer runoff contributes a nitrogen compound called nitrate when it mixes with water that ends up in the groundwater and perhaps your drinking water. Unfortunately, nitrate levels can have serious effects on human health, such as increasing the risk of miscarriages, low birth weight, preterm birth, birth defects, and numerous cancers. Consequently, use less chemical fertilizer and apply only if it’s necessary. Fertilize after mowing and just before it rains to allow the fertilizer time to soak into the ground. Remember that cool-season grasses go dormant during the hot mid-summer, so don’t fertilize then or during periods of extreme heat or drought. Fall rains will return your lawn to its former green color. For more information on fertilizers, please ask any Master Gardener or your local University of Illinois Extension Office.

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