Consumer Reports has no financial relationship with advertisers on this site.
When the dog days of summer bring on their swelter, it’s time to rethink how you mow your lawn.
Though a low-cut, manicured lawn might seem ideal, turf grass actually does better in the summer heat when you let it grow a bit. Longer shoots mean deeper roots, which the lawn needs to suck up moisture from the soil. A shaggy lawn also shades the soil, minimizing evaporation.
To achieve that look, you’ll need to raise the height of your lawn mower’s deck—that is, the machine’s main body, which houses the blade. Lawn mowers today, including the top-scoring models in our lawn mower ratings, have height adjustment levers that make it easy to raise and lower the deck. You’ll actually need to use a ruler to determine the precise setting, at least until you get familiar with your machine.
After the spring growing season, CR recommends letting grass grow to about 4½ inches before mowing it to 3 to 3½ inches. When the heat starts to ease off later in the season, you can drop back down to 2½, for a more manicured look. Here’s how to adjust the deck and clean it to keep your mower in peak condition.
Step 1: Measure Current Cutting Height
Roll the mower onto a level surface, like the driveway or garage floor. If it’s a battery-powered mower, ensure it doesn’t start up while you’re working by removing the safety key. To take the same precaution with a gas mower, detach the spark plug wire from the spark plug; it’s typically located on the front of the mower. “The wire is insulated by a rubber casing and takes some wiggling to get off,” says John Galeotafiore, head of Consumer Reports’ home improvement testing. “But it’s not that hard to do, and the wire and its casing reattach easily to the spark plug.”
Lift up the side or rear-discharge flap covering the opening that expels cut grass. You’ll see the blade inside. Determine the current blade height by measuring the distance between its bottom edge and the ground.
It’s worth noting that most manufacturers ship mowers from the factory with their decks in the lowest position—often as low as 1½ inches, which can scalp a lawn even during ideal weather conditions.
Step 2: Adjust the Deck Height
Lawn mowers come with notched adjustment levers that raise and lower the wheels, thus changing the distance between the deck and the ground. For walk-behind mowers, there may be one lever for each wheel, one lever for the rear wheels and another for the front wheels, or a single lever for all four wheels. With riding mowers, one lever moves the deck up and down, independent of the wheels.
We find that all configurations are easy to operate once you get the hang of it. But the notches don’t always provide a corresponding cutting height, so it couldn’t hurt to take a measurement with your ruler after making the adjustment to ensure you’re at the correct cutting height.
Step 3: Clean the Deck
Grass clippings tend to stick to the underside of the deck, especially if the lawn is damp. If the clumps get bad enough, they can start to restrict airflow inside the deck, which will compromise cutting performance. Dried clippings and clumps are a pain to remove, so it’s best practice to clean the deck after each mowing.
Some mowers have a washout port where you can connect your hose, though a plain old rag will also do the trick. Just be sure to wear heavy gloves to protect your hands from getting cut by the blade. Each time you do this, play it safe by again removing the spark plug wire of a gas mower or the safety key of a battery-powered machine.
To help prevent future buildup when cutting grass, coat the cleaned, dried deck with silicone spray, available at home centers or hardware stores. And keep an eye on the blade’s sharpness. Ideally, have it sharpened—at a hardware store or lawn mower dealer—at the the start of the season and at least one more time during the season, especially if you have sandy or rocky soil.
“Sandy soil acts like an abrasive and will dull the blade more quickly,” says Galeotafiore. “With rocky soil there’s the possibility you can hit small stones and cause the blade to dull or chip.”
If the blade is very dull, you can replace it yourself without a lot of effort. (Watch “How to Replace a Lawn Mower Blade” for our step-by-step guide to this maintenance essential.)
CR members with digital access can see ratings and reviews below of our top picks for walk-behind mowers that will keep your grass trimmed to the perfect height. We’ve highlighted gas and battery-powered walk-behind mowers that perform well across the board and rate well in our evenness test, ensuring a uniform, carpetlike cut.
Finding the Perfect Lawn Mower
Is your lawn mower failing to make the cut? On the “Consumer 101” TV show, Consumer Reports expert John Galeotafiore explains to host Jack Rico how to find the best mower for your needs.
Consumer Reports is an independent, nonprofit organization that works side by side with consumers to create a fairer, safer, and healthier world. CR does not endorse products or services, and does not accept advertising. Copyright © 2020, Consumer Reports, Inc.