With the dog days of summer approaching, kids across the country will be going in for their high-and-tight hot-weather haircuts. For lawns, it’s just the opposite. Turfgrass does better in the summer heat when you let it grow out a bit, since 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.

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 when cutting grass. But you’ll need to use a ruler to determine the precise setting—at least until you get familiar with your machine.

During the hottest weeks, CR recommends letting the grass grow to about 4½ inches before mowing it to 3 to 3½ inches. When the temperature starts to dip again, you can drop back down to 2½, for a more manicured look. The video here walks you through the deck adjusting process and also includes an essential cleaning tip that will help 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. Play it safe by removing the spark plug so that there’s no way the engine can turn on. Lift up the side or rear-discharge flap so that the blade is accessible. Then determine the current blade height by measuring the distance between it 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 1.5 inches, which can scalp a lawn even during ideal weather conditions.

Step 2: Adjust the Deck Height

Lawn mowers come with notched adjustment levers on their wheels. 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.  

We find all configurations easy to operate, once you get the hang of it. But the notches usually don’t provide a corresponding cutting height, so you’ll need to take a second 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 good practice to clean the deck after each mowing.

Some mowers have a washout port that you hook up to your hose, though a plain old rag does the trick; just be sure to wear heavy gloves to protect your hand from getting cut by the blade.

To help prevent future build-up when cutting grass, spray the cleaned, dried deck with silicone spray, available at a home center or hardware store. And keep an eye on the blade’s sharpness. If it looks dull, watch How to Replace a Lawn Mower Blade for our step-by-step guide to this other essential mower maintenance measure.