1 Know the Numbers
When you buy fertilizer, you'll see three numbers on the label. These numbers show the percentage of nitrogen, phosphate, and potassium, respectively, which are the primary nutrients needed to feed your lawn. 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. The 20-5-10 mixture is a good basic mix for spring.
2 Use a Slow-Release With the Right Amount of Nitrogen
Slow-release fertilizers break down their nutrients over a longer period of time, so you can wait longer between applications. "With slow-release, you can go every six to eight weeks, depending on your watering, instead of every four weeks," Turnbull says.
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 says. "The secret is to get it as green as possible without growing it fast." Turnbull recommends giving your lawn between 2 and 3 pounds of nitrogen over the entire growing season. "If you go with 25-0-4, that gives you 1 pound of nitrogen, so over four weeks, that's a quarter pound per week," Turnbull says. "That's too much. At that point, you're baling hay instead of mowing a lawn.
3 Go With Granules
When pros apply fertilizer, they often pull up in a tanker truck and spray your entire lawn in an impressively short amount of time. But pros do this every day, so they know how to factor in the wind and make sure the yard gets even coverage and have the equipment to get the job done right. Homeowners, on the other hand, should use granules and apply them with a spreader.
"Granular fertilizer is very easy to apply accurately," Turnbull says. "When you're spraying, it's tough for a nonprofessional to get a consistent application across the lawn."
4 Plan 5 Applications—and Start Now
Turnbull says to give the lawn its first feeding of fertilizer in the spring when the soil temperature reaches 55 degrees Fahrenheit. Your local university extension office can give you the soil temperature, but you'll know when the soil warms up to 55 because the lilacs begin to blossom and the grass starts growing. For most parts of the country, that means the first feeding should take place by about mid-April. So if you haven't started, now's the time.
The second feeding should happen about four weeks later, in early to mid-May. Then fertilize every six to eight weeks after that through October (see tip 5 for whether you should choose six- or eight-week intervals). For the third feeding, use an organic material, such as manure, instead of a traditional fertilizer.
And remember that fall feeding is critical. "Grass is still growing in the fall. The roots are going down and they need fertilizer," Turnbull says. "This is the most important application of the year."
5 Don't Forget About Watering
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 a sprinkler system, you'll need to fertilize about every six weeks. Without a sprinkler, you can wait another two weeks between feedings.
Be sure to read what the fertilizer label says regarding watering before or after the application. Granules need moisture to break down, and some fertilizers require you to wet the lawn with about a quarter-inch of water before applying them.
6 Fill 'er Up and Close the Hopper
When you're ready to fill the spreader, park it in the driveway—or, if you can't, at least put a tarp under it. This keeps any spilled granules from accumulating in one stop on the lawn, where it can burn and kill the grass.
"Make sure your hopper is shut when filling up the spreader," Turnbull says. "That's lesson number one that everyone forgets at least once."
A broadcast spreader is a better choice than a drop spreader for homeowners. Broadcast spreaders are easier to use, and since they disperse the fertilizer a wider distance, there's less chance you'll end up with strips in your yard casued by not overlapping the rows properly. Plus, at my local Lowe's, broadcast spreaders are significantly cheaper. They start at $32, while drop spreaders start at $84.
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7 Apply, but Don't Over-Apply
The fertilizer label will give you the application rate. But don't follow it. "Start out at half of what's recommended on the bag," Turnbull says. "One of the biggest mistakes I see is going with the spreader wide open."
He recommends spreading the fertilizer at half the recommended rate, or slightly less, in one direction on the lawn, then spreading it again at half the rate in a perpendicular direction. This pattern gives better coverage and helps prevent over-applying. "Too little is better than too much. I always recommend to err on the side of too little," Turnbull says.
Cover the perimeter of the yard first, then fill in the middle. 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 tire track to tire track," Turnbull says. "This ensures good coverage."
8 Sweep Up Stray Granules
Sometimes, fertilizer ends up on your driveway or patio, despite your best efforts. If that happens, sweep it up rather than letting the rain wash it away.
"If you don't sweep it up, it just adds extra pollution," Turnbull says. "It gets washed away and ends up in the rivers and streams. Sweeping up the fertilizer is good for nature."