Clumps of grass when mowing with a John Deere lawn mower can be due to grass conditions or a problem with the mower deck. These problems are usually easy to correct by mowing dry grass at the correct height, sharpening mower blades and cleaning the mower deck. If you still get a few lumps, even after mowing in good conditions and performing maintenance on the mower, mowing over the clumps again can distribute them more evenly.
The main cause of grass clumping when the lawn is mowed is cutting wet grass. This problem can occur with any mower, including a John Deere. Mowing after there has been a rain shower or after watering the lawn means the grass will stick together in clumps. Wet grass is also more difficult for the mower to cut, and can quickly lead to dull mower blades. When the grass is dry, it will be spread across the lawn evenly so it can decay and return nutrients to the soil.
Ideal mowing heights vary according to the species of grass. For example, zoysia grass (Zoysia spp.) should be maintained between 1/2 and 1 1/2 inches tall, while St. Augustine grass (Stenotaphrum secundatum) does best when kept between 1 and 2 inches tall. Zoysia grows in U.S. Department of Agriculture plant hardiness zones 6 through 9, while St. Augustine grass grows in USDA zones 8 through 10. Letting grass become overgrown, or cutting more than one-third of the overall height at once, can cause the long grass blades to clump.
Dull Mower Blades
Over time, normal mowing causes the mower's cutting blades to become dull. Cutting when the grass is overgrown or wet can speed this process up. Once the blades are no longer sharp, they tear the grass rather than cutting cleanly. This can increase the risk of disease, give the grass an uneven appearance, and cause clumping on the lawn. This problem is easily corrected by sharpening or replacing the blades. Using mulching blades designed for use in John Deere mowers can also help prevent clumping.
Clogged Mower Deck
Even when cutting grass that is not overgrown and that has not been watered recently, the clippings may still clog the mower deck. This can be caused by water stored in the grass leaves. Periodically cleaning the John Deere mower deck to remove grass buildup will prevent matted clumps from ending up on the lawn. Cleaning the mower deck can also reduce the risk of mechanical problems and damage to the blades.
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