The Quick and Easy Guide to Lawn Fertilization

The very best time for lawn fertilization is in the spring, when the soil temperature—not the air temperature—reaches 55º Fahrenheit. You’ll know when the soil warms up to 55º because the lilacs will begin to blossom and the grass will start growing.

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Or, buy a soil thermometer and check the temperature at any time. In most parts of the country that means the first application of lawn fertilizer should take place by about mid-April. So, if you haven’t started yet, mark that date.

When shopping for fertilizer, you’ll find three numbers printed on the label. These numbers represent the percentage of nitrogen, phosphate, and potassium, respectively, which are the primary nutrients needed to feed your lawn.

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So, a 20-5-10 bag will have 20 percent nitrogen, 5 percent phosphate, and 10 percent potassium. The rest of the bag usually contains filler material that helps ensure an even application of the fertilizer. By the way, a 20-5-10 lawn fertilizer is a good basic mix to use in spring.

Slow-release lawn fertilizers break down their nutrients over a longer period of time, so you can wait longer between applications. “With slow-release fertilizers, you can feed your lawn every six to eight weeks, depending on your watering schedule, instead of every four weeks,” Turnbull says. That saves you both time and money.

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He recommends a slow-release that contains nitrogen, but not too much. “The most nitrogen you need on a lawn is one-tenth of a pound per week. The grass can’t get any greener than that. If you use more, you’re only going to make the grass grow faster so you have to mow more often,” Turnbull explains.

“The secret is to get it as green as possible without growing it fast.” Turnbull recommends giving your lawn between two and three pounds of nitrogen over the entire growing season. “If you go with 25-0-4 fertilizer, that gives you one pound of nitrogen. So, over four weeks, that’s a quarter pound of nitrogen per week, which is way too much,” Turnbull says. “At that point, you’re baling hay instead of mowing a lawn.”

When professional landscapers apply fertilizer, they often drive up in a tanker truck and spray your entire lawn in a remarkably short amount of time. But pros do this every day, so they know how to factor in for the wind and make sure the yard gets even coverage. And they have the proper equipment to get the job done right. Homeowners, on the other hand, should use granules, which are super simple to apply using a spreader (see tip No. 7).

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“Granular fertilizer is very easy to apply accurately,” Turnbull says. “When you’re spraying fertilizer, it’s tough for a homeowner to get a consistent, even application across the entire lawn.”

As mentioned earlier, Turnbull recommends giving your lawn its first feeding of fertilizer in the spring—mid- to late-April in most regions—once the soil temperature reaches 55º Fahrenheit. Your local university extension office can give you the soil temperature in your neighborhood, but again, you can use a soil thermometer or wait until the lilacs blossom, as an indicator that the soil is 55º.

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Now, the second feeding should happen about four weeks after the first application, around mid-May or so. Then fertilize every six to eight weeks after that straight through to October. For the third feeding, use an organic material, such as manure, instead of a traditional lawn fertilizer.

And remember that fall feeding is critical, too. “Grass continues to grow throughout the fall. The roots are going down into the soil and they need fertilizer,” Turnbull says. “In fact, this is the most important application of fertilizer for the whole year.” And use a fall fertilizer that’s slightly higher in phosphorous and potassium, which will promote better root growth.

Contrary to what some people think, the more you water your lawn, the more fertilizer it needs. “With more water, there is more growth, so you need more fertilizer,” Turnbull says. “As the grass grows, it uses more nutrients.” If you have an automatic sprinkler system, you should fertilize your lawn about every six weeks. Without a sprinkler system, you can wait an additional two weeks between feedings.

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Also, be sure to carefully read the fertilizer label to learn whether you should water the lawn before or after applying the fertilizer. Granulated fertilizers need moisture to break down, and some fertilizers require you to soak the lawn prior to application.

When you’re ready to pour fertilizer into the spreader, park it on the driveway or patio. If you can’t, at least put a tarp under it. This will keep any spilled granules from accumulating in one spot on the lawn, where they can burn and kill the grass. “And make sure your hopper is shut before filling up the spreader,” Turnbull says. “That’s lesson number one that everyone forgets at least once.” (If the hopper is left open, the fertilizer will pour right through onto the ground.)

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A broadcast spreader is a better choice than a drop spreader for homeowners. Broadcast spreaders are easier to use, and since they disperse fertilizer a wider distance, there’s less chance you’ll end up with stripes in your yard caused by not properly overlapping the rows. Plus, broadcast spreaders are fairly affordable, starting at about $50.

To fertilize small yards, use a handheld broadcast spreader, which has a hand crank. You can buy one for as little as $20. These compact spreaders are particularly useful for fertilizing narrow side yards, and grassy areas along fence lines, around trees, and behind garages and sheds.

Regardless of what type of spreader you use, be sure to walk at a consistent, steady pace as you apply the fertilizer. Failing to do so will cause the fertilizer to be spread too thin in some spots and too thick in others.

Every fertilizer label will list the application rate, but Turnbull recommends that you don’t follow it. “Start out at half of what’s recommended on the bag,” he says. “One of the biggest mistakes homeowners make is applying fertilizer with the spreader wide open.” He recommends spreading the fertilizer at half or slightly less than half the manufacturer’s recommended rate.

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Start by applying fertilizer around the perimeter of the yard first, and then fill in the middle, working in one direction. Then, spread it again, moving in a perpendicular direction. This crisscrossing pattern ensures much better coverage and helps prevent over-applying the fertilizer. “When it comes to spreading fertilizer,” Turnbull says, “too little is better than too much. I always recommend erring on the side of too little.” A heavy dose of fertilizer isn’t only a waste of money, but it can burn and kill the grass.

Since you’re applying the fertilizer at half the recommended rate, it won’t spread out very far, so you don’t need to estimate how much spacing to keep between rows. “Go from tire-track to tire-track on the spreader,” Turnbull says. “This will guarantee good, even coverage.”

And be sure to check the weather forecast prior to fertilizing. If you apply the fertilizer right before a downpour, much of the fertilizer will be washed away.

No matter how careful you are, the spreader will occasionally throw fertilizer onto your driveway, sidewalk, or patio. If that happens, sweep it up rather than letting the rain wash it away.

“If you don't sweep up and collect the excess fertilizer, it just adds extra pollution,” Turnbull says. “It gets washed away into storm drains and then ends up in the rivers, streams, and lakes. Sweeping up the fertilizer is good for the environment.”

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Finally once you’ve finished fertilizing your lawn, pour any leftover fertilizer out of the spreader and back into its original bag. Tightly seal the bag and store it away in a cool, dry place, well away from any children and pets.