Winter is clearly on its way, with nearly all the leaves gone from the trees. But that means it's a fine time to think about mulch.
If you hung onto your fallen leaves, you've already got a fine mulch material. Shred the leaves by running over them with the power mower or using an electric shredder to keep them from packing down or blowing around and spread a 2- to 3-inch layer over perennial or vegetable beds, says Doris Taylor, Plant Information Specialist at The Morton Arboretum in Lisle. "They will add beneficial organic matter back into the soil and provide some winter protection," she says. You also can use compost or finely shredded wood mulch.
One of the good things about mulch is that it insulates the soil. That's exactly why it is important not to apply it too early, Taylor says. We want the soil to freeze around the roots of plants and keep them dormant until winter is safely over; we insulate to keep soil frozen during treacherous late-winter freeze-thaw cycles. In fall, "wait until the soil starts to get frosty," even after Thanksgiving, before you spread mulch, Taylor says.
Around trees and shrubs, it's fine to use a chunkier bark mulch, which will break down much more slowly than leaves. Encircle the trunk with a level 3- to 4-inch-deep layer "as far out as practical," Taylor says.
Above all, don't pile the mulch against the tree trunk, where it can cause rot or invite insects and burrowing animals to feast on the bark. Keep it a few inches away from the bark and spread it evenly. Don't bother removing old mulch; just top it off, when necessary, to keep the entire layer about 4 inches deep.
Beth Botts is a staff writer at The Morton Arboretum in Lisle (mortonarb.org).