Posted by: Alison O’Connor, horticulture agent, Larimer County
It’s almost like nature mocks us. We work hard all summer to grow tomatoes, mow the lawn religiously and fend our garden from insects and disease. Just as we want to take a break and watch some college football (Go Rams!…and Cyclones…and Buckeyes), the trees decide to drop their leaves and landscape maintenance continues.
I’ve been asked this question a lot—What should I do with all the leaves that drop? There’s a lot of great ways to use them, including composting, tucking them around newly planted plants, throwing them in the veggie garden to till in next spring or mulching them into your lawn.
Wait…mulch them into your lawn? But doesn’t that cause thatch?
This is one of the great myths of urban horticulture—that mulching leaves (or grass clippings) causes thatch build-up. It doesn’t. Thatch is mostly comprised of living and dead turf roots, stems and shoots. It’s organic matter. And thatch only occurs on certain turf species—bluegrass and bentgrasses are thatch formers. Tall fescue and perennial ryegrass are not (they grow in clumps). Thatch will happen on bluegrass regardless if you collect your clippings or leaves. So mulch them in and reap the benefits.
Some fascinating research at Michigan State University has found that mulching fallen leaves into your lawn can decrease weeds and fertilizer use. Yes, you read that correctly: mulching leaves can decrease weeds in the lawn. The small leaf chunks fill in soil gaps in turf areas. These open soil spaces are perfect for weeds to germinate. In fact, MSU researchers found that after only three years of mulching leaves into the lawn, they found nearly 100% decrease in crabgrass and dandelions. That alone should convince you to mulch your leaves.
The fine Spartan researchers also found no effects on turf quality after mowing up to 6” of leaves at a time. They found the color, quality and density of the turf remained. And mulching leaves into the lawn resulted in quicker spring green-up because of a small fertility effect (most leaves contain 1-2% nitrogen). So over time, if you mulch your leaves faithfully (and your clippings), you will reduce fertilizer inputs to your lawn. Plus, the mulched leaves hold in soil moisture.
Here’s the key: set your mower height as high as possible and make sure that you can still see some green grass following mowing—you may have to make two passes over the lawn. If the leaf layer is too thick, it may not break down rapidly enough and can act like a mat on the turf surface. So mowing leaves frequently (once or twice a week) is best.