Lots to love about leaf mulch

The word is out: leaf mulch is great. 

Shredded leaves make high-quality, free mulch

   I’ve been chopping up fall leaves for mulch since sometime in the 1990s. These days I mulch most beds with whole leaves, because they provide shelter for over-wintering insects. I still use chopped leaves for areas near the lawn, because they don't blow around. 

     Many people chop leaves with the lawnmower. I prefer to use a standing leaf shredder, essentially a string trimmer in a drum. Plastic filaments whirl around and chop the leaves into small shreds. The resulting mulch is pretty, it doesn’t blow around like whole leaves left on the ground would, and it’s great for building soil fertility. And the electric-powered shredder doesn’t generate exhaust.

Electric leaf-shredder doesn't pollute the air

    The Rose Kennedy Greenway, the linear Boston park created in 2008 when the Big Dig moved the highway underground, uses organic methods and has recently experimented with switching from bark mulch to shredded leaves. The product they apply, which you can now buy from landscapers, has a step added to my process. After the leaves are chopped, they’re composted for a year. Horticulturists for the Greenway find the composted leaf mulch is full of beneficial soil organisms.

Rose Kennedy Greenway-photo Tim Grafft/MOTT

    As their test area, the Greenway chose a section of the garden devoted to New England native plants. After three years, they’ve found substantial benefits. In the leaf mulch beds they’ve measure increases in soil organic matter. They’ve also found increased cation exchange capacity, which allows soil to hold on to nutrients and buffers it against excess acidity. In fact, the soil in these beds has improved so much that Greenway staff have to consider whether the soil may become too rich for their native plants.

    One of the few drawbacks of leaf mulch at the Greenway has been small fires in the mulch from discarded cigarettes, which apparently isn’t a problem with bark mulch. Let’s hope visiting smokers can learn not to throw cigarette butts into the garden!

It counts as littering

    The City of Newton passed on a recommendation from Michigan State University for mulching lawns with chopped leaves. Lawn lovers hate the idea of letting leaves lie on lawns through the winter, where snow piled on matted leaves can kill the grass. That’s is one of the reasons for our suburban cultural taboo against letting fall leaves lie.

No fall leaves allowed on the lawn

    Instead of doing all that work raking and bagging the leaves, though, MSU turfgrass scientists found they could save time and improve lawns by chopping the leaves on the lawn with a few passes of a lawn mower. The little leaf fractions sift down out of sight among the turf plants, providing a mulching function that suppresses dandelions and crabgrass by up to 100 percent after three years. The decomposing leaf shreds also fertilize the lawn.
 

Chopping leaves with a lawnmower-photo Rebecca Finneran, MSUE

    My focus when I chop up fall leaves has been on improving the soil for shrubs, vegetables and perennials. The lawn is on its own. But after hearing the MSU results, I think I’ll set up my leaf shredder on the lawn this fall to spread some of those leaf bits around while I make mulch for the beds.

Perennials could share some leaf mulch with the lawn

    I’ll be demonstrating the leaf shredder in action at a hands-on sustainable gardening course in my yard Saturdays October 26 and November 2. You can sign up here through Newton Community Education.