Why Does Grass Build Up Under the Lawnmower Deck?

The airflow due to your lawnmower’s blades propels the cuttings into a bag or outside onto your lawn. Grass buildup below the lawnmower deck is usually minimal, and can be cleaned once a year. However, occasionally grass builds up beneath the deck more often, or in more volume, than normal. A number of the causes of a grass buildup below your mower deck can easily be prevented.

Wet Grass

Grass clippings building up more than usual below your mower deck might be caused by moisture from the grass when you cut it. Wetness causes the grass to clump, which makes it more inclined to stick to the bottom of the deck. To prevent this, allow the grass dry out for a day or 2 after it rains, even if it feels dry to the touch. Grass can also be moist from dew in the mornings, so mowing in the late day gives it time to dry and prevents clumping.

Grass and Reducing Height

Occasionally grass may develop under the mower deck should you mow when the grass is too long, or if you cut too low to the peak of the grass. To prevent accumulation of grass on the mower deck, then set the blade so you’re only cutting the top 1/3 of the grass blades on each pass. If the grass has grown excessively long, it is much better to make 2 passes, cutting only 1/3 of the blades each time.

Dull Blades

Your mower runs most efficiently with sharp blades. Dull blades not only increase the probability of grass buildup below the deck, they also shred the grass tips. This can give the lawn a brown mixture, and cause wear on the mower’s engine, bearings and belts. Sharpen your mower blades once a year to make certain they’re cutting correctly.

Removing the Buildup

To clear grass buildup below your lawnmower deck, then switch off the mower and rinse the bottom with a spray of water in the garden hose. Some mowers also arrive with a wash-out port — an opening in the deck in which you insert the end of a hose. After the water is turned on, it sprays around the deck to clean away debris. Do this immediately after mowing, before the clippings have enough time to dry and harden. If the grass is hardened, use a stiff bristle brush to loosen it, rinse it off with water.

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