When you tidy up the garden after the winter, don’t tidy it too much. “Make sure you leave the mulch layer that covers your garden’s soil,” said Sharon Yiesla, plant knowledge specialist in the Plant Clinic at The Morton Arboretum in Lisle. “And if you don’t have a mulch layer, make sure mulch is part of your plans for spring gardening.”
A mulch layer is a covering of plant matter over the soil. It can be made of “any material that comes from plants,” she said. Most gardeners think of “mulch” as a commercial product, sold in bags or by the cubic yard, that consists of shredded wood. A mulch layer also can be formed of dried leaves, straw or wood chips from tree work.
Mulch has many benefits. It protects the roots of your trees, shrubs, perennials and other plants. A layer of mulch also insulates the soil against temperature extremes. As it breaks down, it adds nutrients to your soil and improves conditions for your plants.
An area of mulch surrounding a tree does more: It forms a safety zone that will keep away lawn mowers and string trimmers that can damage the tree’s bark.
The mulch around a tree or shrub should be a wide, even layer about 3- to 4-inches deep, Yiesla said. “Spreading it any deeper won’t help and may keep air and water from reaching the roots,” she said.
It’s especially important not to pile mulch against the trunk of a tree. “Piled-up mulch can harbor insects, diseases and rodents,” she said. “It also traps moisture and can cause the tree’s bark to rot.” It’s common to see trees with heaps of mulch around them, but that mulch has been applied incorrectly.
– Original Credit: Beth Botts
Many gardeners use the leaves that fall in autumn as a source of free mulch for the winter months, raking them over beds and around trees and shrubs. By spring, many of those leaves will have decayed, but others may become a dense mat that can interfere with the sprouts of bulbs and other plants.
Where it’s necessary, “fluff up the leaves with your leaf rake so the new sprouts can push through,” Yiesla said. “Just fluff them. There’s no need to clear them away. They are still valuable as a mulch layer.”
If there’s a spot where leaves have piled up, remove some of them and add them to your compost pile. Keep enough leaves in place to provide protection and nutrition as they decay. It’s a good idea to rake leaves off the lawn, so sunlight can reach the grass.
Mulch continually decays from the bottom of the layer — “that’s how it adds nutrients to the soil,” Yiesla said. Over time, this decay will consume the mulch. If the mulch layer around trees or shrubs or in perennial beds has gotten thin, you can replenish it without removing the old mulch.
“It will look best if you use the same kind of mulch,” she said, “but that won’t really matter to the plants. All they want is for their roots to be covered with some kind of natural material.”
Be careful, when you fill in thin mulch, not to make the layer too deep. “Old and new mulch together should still be just 3- to 4-inches deep around trees and shrubs and 1- to 2-inches deep in perennial and vegetable beds,” she said.
If you have a stash of fallen leaves from last autumn, you will be ready to spread a mulch layer over all the new plants you add this spring. Otherwise, make sure mulch is on your spring garden shopping list. “Spreading mulch over the soil is important for anything you plant,” Yiesla said.
For tree and plant advice, contact the Plant Clinic at The Morton Arboretum (630-719-2424,mortonarb.org/plant-clinic, or [email protected]). Beth Botts is a staff writer at the Arboretum.