Should you mulch leaves into the lawn or bag them?

What does the research say?

MSU Extension’s turf work found that leaves mowed into a lawn break down in the turf rather than smothering it, as long as they are chopped finely. A mulching mower can handle up to about 6 inches of leaves at a time, depending on the mower; a push mower handles less and may need two passes. Oak and maple leaves were both used with no harm to the lawn, and over several years the mulched plots had fewer dandelions and crabgrass, because the leaf bits filled the gaps where weed seeds would otherwise sprout.

How to do it

• Mow when the leaves are dry or barely damp, not wet. Wet leaves clump, strain the engine and leave a mat instead of fine pieces.
• Keep the deck at your normal height, not lower.
• Make two passes if you can still see whole leaves after the first.
• Aim for dime-size bits sitting down between the blades, with grass still visible on top.

After a few days the bits sift down and disappear.

When should you bag leaves instead?

• The layer is too thick for your mower to chop in one or two passes.
• The leaves are already wet and matted after a week of rain.
• There are lots of sticks, nuts or seed pods mixed in.
• The leaves are in beds, under shrubs or against the foundation, where a mower cannot go.
• The tree had a leaf disease you do not want sitting in the lawn.

Bagged leaves go out in paper yard-waste bags or a marked can, never plastic, before your community’s last pickup. See leaf pickup and yard waste rules by community.

Do you need to fertilize after mulching leaves?

Not to break the leaves down. A University of Missouri summary of the leaf-mulching research notes that adding nitrogen fertilizer improved the look of the turf but did not make the leaves decompose any faster. The chopped leaves break down on their own over the following weeks. Whether your lawn needs fall fertilizer is a separate question, and one for a lawn treatment company: we do not apply fertilizer or any other product.

Keep them out of the street

Whichever way you go, blow the leaves onto the lawn or into a pile, not into the street. Macomb County Public Works asks residents to keep leaves and grass out of storm drains, which carry untreated water toward Lake St. Clair; leaves clog the drains and feed algae, and in Mount Clemens and Center Line leaves in the street break local ordinance.

What about leaving them on the lawn?

A scattering is fine. A layer thick enough to hide the grass is not: over a Michigan winter, matted leaves block light, hold moisture against the turf and raise the risk of snow mold, and the lawn comes out thin in spring.

Leaves you cannot use on the lawn

Use them elsewhere. Shredded leaves make good mulch for beds, and they compost well. Michigan has banned yard waste from landfills since 1995, so the household trash cart is not an option.