For most routine mowing, mulching or leaving grass clippings on the lawn is the better choice. Clippings return nutrients to the soil, reduce yard waste, and do not normally cause thatch when the lawn is mowed properly.
When to Mulch Grass Clippings
Leave or mulch clippings when they are short enough to filter back into the turf and the lawn is not excessively wet or diseased. A mulching mower can chop them more finely, but a conventional mower can also return clippings successfully when you mow often enough.
Benefits of Leaving Clippings
- Returns nitrogen and other nutrients to the lawn.
- Reduces the need to handle and dispose of yard waste.
- Saves time compared with bagging.
- Does not significantly contribute to thatch under normal mowing conditions.
When to Bag Grass Clippings
Bag or remove clippings when they are so long, wet, or heavy that they form mats and smother the turf. Removal can also be appropriate when mowing a lawn with certain active disease problems if extension guidance for that disease recommends collecting infected material.
If weeds have mature seed heads and you are trying to prevent seed spread, bagging that mowing can also be reasonable.
Do Grass Clippings Cause Thatch?
No, not under normal conditions. Grass clippings break down quickly because they contain a high percentage of water and relatively little lignin. Thatch is composed mainly of more decay-resistant stems, crowns, roots, and rhizomes.
How Much Should You Mow Off?
Follow the one-third rule when practical: avoid removing more than about one-third of the grass blade height in a single mowing. If the lawn has become very tall, reduce the height gradually rather than scalping it and leaving a heavy layer of clippings.
What to Do With Bagged Clippings
Clean, pesticide-free clippings can be composted or used appropriately as mulch in other parts of the landscape. Avoid using clippings in vegetable gardens or compost in ways that conflict with the label restrictions of any herbicide recently applied to the lawn.
Bottom Line
Mulch or leave clippings most of the time. Bag them only when they are excessively heavy, wet, diseased, or likely to spread mature weed seeds. Returning normal clippings is an efficient and sustainable lawn-care practice.
Sources: University of Minnesota Extension — What to do with lawn clippings; University of Illinois Extension — Grasscycling.
