If this is the year that you’ve decided to achieve the perfect lawn, then you’re probably looking into fertilizing.
After the basics like mowing and watering, fertilizing is the next step in getting the kind of healthy, green, beautiful lawn that’ll make neighbors jealous and fathers proud.
But you don’t want to just grab a bag of pellets and start spraying it willy nilly on the grass! Making the most of your fertilizer session is a matter of good timing—and not overdoing it.
To help understand the basics of lawn fertilization, we asked Jason Lanier, a turf management Extension Specialist at the University of Massachusetts Amherst, to address the biggest questions every homeowner should consider before heading to the garden store.
Does Every Lawn Need to Be Fertilized?
In short, yes. Nearly every lawn can benefit from fertilizer.
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“Like all plants, grasses need certain essential nutrients,” says Lanier. “Some older, low maintenance lawns may not need much fertilizer input, but most lawns can benefit.”
If your lawn is experiencing slow growth, thinning, color changes like yellowing, or if it endures stresses like insects, diseases, and traffic then, Lanier says, applying fertilizer can help.
More Expert Lawn-Care AdviceHow Often Should I Fertilize My Lawn?
How often you want to fertilize is largely a matter of taste, as well as the specific needs of your lawn, says Lanier.
While a number of national lawn care companies advertise “4-step programs,” creating a widespread belief that once per season is optimal, it’s not always necessary. “One survey of households on Cape Cod revealed that the average homeowner fertilized just under 1.5 times per year. I fertilize my own lawn twice per year,” he says.
Is There a Wrong Time to Fertilize My Lawn?
“Absolutely,” says Lanier. You want to time the fertilizer “to correspond with maximum turf grass growth.” Otherwise the nutrients may be wasted.
Actually, they’re worse than wasted, as the excess nutrients can cause environmental problems: “Nitrogen and phosphorus especially,” says Lanier, “can be pollutants.”
This means “avoid applying nutrients too early in the spring, during summer drought,” (unless you’re irrigating enough to keep the grass growing), “and late in the season when plants will soon be dormant for winter.”
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What Are the Risks of Over-Fertilizing?
You might think that if a little fertilizer will help keep the grass healthy, then a lot of fertilizer will really get it looking great. But this is wrong. In fact, “Adding more nutrients than the plants need can actually be detrimental,” says Lanier. For example: the more nitrogen that is available to a plant, after a certain point, the worse the plant’s roots grow.
It doesn’t just harm the plant, either. “Nutrients like nitrogen and phosphorus are considered pollutants” in excess, says Lanier, “especially for ground and surface water.” There are even laws in some areas that limit the amount of nitrogen and phosphorus that can be applied in order to manage these risks.
“When it comes to nutrients, the goal should always be just enough, and no more,” says Lanier
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How to Ensure Even Fertilization
To figure out just what you need—and to apply it evenly—you’ll need to do a little math.
“Know the square footage of the area that you intend to fertilize,” says Lanier, “so you don’t apply too much (or too little).”
“Another important step is to ensure that your spreader is properly and accurately calibrated,” says Lanier. An improperly calibrated spreader can end up adding too much fertilizer to one area, and not enough to another, resulting in patchy grass.
After calibrating, but before beginning, you want to think a little about your path around the yard. “With a broadcast spreader (most often used for granular applications) you want to make sure that you’re allowing for proper spacing between passes,” says Lanier. “Too close, and you’ll overlap. Too far apart, and you will miss some areas. With most broadcast spreaders the objective should be to throw material “wheel track to wheel track” to achieve the correct spacing.”
Another trick for uniform fertilizing, suggests Lanier, is to “divide the material in half based on the proper rate, and apply in two half-rate applications. Typically the second application is made at right angles to the first.” So if you spread walking north and south with half the fertilizer, and then again walking east and west with the other half, you’ll have achieved a more even coverage.
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What Is the Best Kind of Fertilizer?
In general fertilizer is available in three main forms: granules, sprays, and natural/organic fertilizer, such as compost. While Lanier doesn’t want to name one as better than the others, he does allow that one is certainly more popular. “Most homeowners (and many professional practitioners) choose granular materials because they are readily available, convenient, and easily applied,” he says. “Liquid fertilizers require more specialized equipment.”
As for organic fertilizer, “applications, can be more labor intensive, relatively speaking, but again this is a matter of preference.”
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Beyond the form it comes in, another important consideration, says Lanier, “is what percentage of the nitrogen in the material is slow release.” Since nitrogen is the nutrient that grass responds the most to, many fertilizers contain some combination of quick-release and slow-release nitrogen.
“Too much readily available nitrogen,” warn Lanier, and your grass will “surge,” growing faster than you want. It can also “cause burning, and is more likely to contribute to loss and waste.” A higher proportion of slowly-available nitrogen can be preferable, therefore, as it will “better match plant activity, leading to more effective nutrient capture and a measured growth rate.”
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Should I Do a Soil Test Before Fertilizing?
“A soil test,” says Lanier, “is always an excellent place to start. Results will provide data on nutrient levels and pH, and also recommendations for fertilization and any necessary pH adjustments.” You can typically get a soil test from your local university cooperative extension program, for a nominal fee. (Find your nearest extension here.)
“One important note here is that there is no available soil test for nitrogen,” says Lanier. Because nitrogen levels don’t remain consistent in soil, a test wouldn’t be useful for more than a few days or weeks. Instead, says Lanier, “nitrogen application rates instead should be based on factors like expectations, the turf species, how hard you plan to use the turf, and the resources available for care.”
Some areas also have environmental regulations that may dictate what is allowable. Typically, you can expect to apply “around 1 pound of nitrogen per 1000 square feet, per application” says Lanier. Or “between 1 and 4 pounds of actual nitrogen per 1000 square feet, per season.”
Other Fertilizing Tips
Here are a few final tips from Lanier:
Pay attention to local fertilizer regulations that dictate what can be applied and when. These most often apply to nitrogen and phosphorus.Read the fertilizer label, and be aware specifically about how much nitrogen, phosphorus, and potassium—sometimes called the NPK number—is in the material. Within the nitrogen content, be sure to determine the percentage that is in a slow-release form. Be aware that many granular fertilizers are packaged these days as “combination products” and include insecticides or herbicides along with the fertilizer. These can be convenient if you happen to need all those things, but often you sacrifice control over the rate or timing of some of the included materials. In many cases it’s better to apply materials separately and on an as-needed basis.
Jason Lanier is an Extension Specialist and Group Leader, specializing in Turf Management at the UMass Amherst Extension, in Amherst, MA. Jason’s professional expertise is in plant stress physiology, water and nutrient management, and sustainability among other things. Learn more about Jason here.