As a rule, you should not really mow the lawn when the grass is wet and never remove more than one third of the leaf blade when mowing. If you absolutely have to mow when the grass is wet and/or has become very long, clumping is likely to happen.

Clumps of grass clippings shouldn’t be left on top of the turf. It’s best to disperse the clumps on the lawn with a fan rake or blower. Excessive clumping may require raking the clumps up and removing them. If left on the lawn for too long clumps can suffocate the grass beneath it, turning it yellow.

To reduce clumping:
• mow in the afternoon when grass is more likely to be dry
• don’t let the grass get too long between mowings
• raise the height of cut
• use mulching blades
• clean under the mowing deck periodically
• don’t over-fertilize