Clumps of grass clippings shouldn't be left on top of turf. It's best practice to disperse the clumps on the lawn with a fan rake or blower. Excessive clumping may require raking the clumps together, placing them in a lawn waste bag, and removing them. If left on the lawn for too long, clumps can suffocate the grass beneath, turning it yellow. The following tips will help you reduce grass clumps in your yard.
Mow When It's Dry
As a rule, don't mow the lawn when the grass is wet and never remove more than one-third of the leaf blade when mowing. Mow the yard only when the grass is dry. Wet grass is much more likely to form clumps than dry grass. Avoid mowing after rainstorms or early in the morning when dew remains on the ground. If you absolutely have to mow when the grass is wet and/or has become very long, clumping is likely to happen. If you find yourself with a very overgrown lawn, you may want to start the process with a weed wacker. Once you've cut down the extra long grass and collected the initial clippings, you can proceed with your mower as usual.
Don't Wait Too Long
Don't let the grass get too long between mowings. When the grass gets too long, mowing throws out clumps everywhere or creates a bagging nightmare. You can dump these clumps in the compost pile or let them dry for a few days and use as mulch in garden beds. Mow often enough so you’re never removing more than one-third of the blade length at a time. (i.e., It's time to cut when the height gets to four inches, not five or six.) This may mean mowing twice a week or every four or five days when the grass is growing fastest in mid-spring.
Raise the Height of Cut
People often cut lawns too short, causing the risk of more clumping. Mowing too short also increases moisture and nutrition demands as the grass tries to fight back from near decapitation. Weeds germinate best and grow at a faster rate when taller grass blades aren’t in the way. Aim to cut your lawn at 2.5. to 3 inches high–typically the highest setting on mowers. What makes a mown lawn look good is the evenness of the cut, not its height.
Use Mulching Blades
If you mow often enough, you’ll get tiny clips that quickly disappear into the lawn, especially if you’re using a mulching mower. Mulching mowers save a lot of time because clumping is greatly reduced and you won't need to make an extra effort to gather the clippings. Another bonus is that the mulched clippings can also help to improve the overall appearance and health of a lawn. If you're interested in trying a mulching blade, check your owner's manual to see if a mulching kit can be purchased for your mower.
Maintain Your Mower
If you're dealing with a riding lawn tractor, disconnect the mower deck to perform cleaning maintenance. Scrape the bottom of the deck with a plastic scraper or putty knife. Remove all dried grass and mud stuck to the bottom of the deck. Also, thoroughly clean out the discharge chute on the deck. Layers of dried grass and debris can block up the deck, which causes clumps to form as you mow.
Examine the mower blades. If the blades are damaged or dull, replace or sharpen them. Dull or damaged blades will not cut the grass cleanly, which may result in clumping.
Mowers and Mowing Safety. University of Minnesota Extension