Have you ever seen those “mulch volcanoes” around the base of trees? They’re everywhere and maybe even in your own yard. Mulching is very beneficial for retaining soil moisture so the more the better, right? WRONG! Mulch that is too deep can suppress weed growth reducing maintenance but the trade-off is that it damages trees and other landscape plantings.
Problems with Improper Mulching
Deep mulching around trees and landscape plants can stress the plant by retaining too much moisture in the root zone causing root rot. Tree roots need oxygen to breathe and without it will actually suffocate and die. Roots can grow into the mulch crossing over each other and around the tree also causing the tree to decline and die. Mulch that is piled up against the trunks of trees or stems of plants “volcano style” stresses the stem tissues, which invites fungus, insect problems and bark decay. Further, when a thick layer of mulch becomes matted it prevents water and air from nourishing the roots not to mention it is a perfect habitat where rodents can chew the bark damaging the planting.
A properly mulched tree or landscape planting has no more than a 2 to 4 inch layer of organic mulch. The depth of the mulch depends on soil type. Use four inches on light, well-drained soils and only two inches on heavier clay type soils. For a newly planted or established tree or landscape plant begin by removing the grass around its base in a 3 to 6 foot area depending on the size of the tree or plant. Add organic mulch to this area starting about 6 inches from the trunk. Proper mulching helps maintain soil moisture and discourages weed growth. Mulching around trees keeps the lawn mower or weed whacker at bay thus reducing trunk damage. It also acts as insulation for the roots from hot and cold temperatures and gives your planting a neat, cared for appearance.
There are many types of mulch on the market; so what type is best for landscape plantings? Mulches around trees and landscape plantings should be organic in origin. Shredded pine bark, hardwood chips found at many municipal sites, composted wood chips, wood chips with bark and leaves, pine needles, softwood barks, cocoa bean mulch, leaves, or compost are the best types of mulch to use as they replenish soil nutrients. Avoid using sour mulches, grass clippings and inorganic mulches like lava rock, rubber chips, stone or other materials of this type as they do not provide any nutrients, add any organic matter or improve the soil structure.
On an established planting the mulch should only be replenished to the 2 to 4 inch level as the older layer decomposes. Rake up the old mulch layer to break it up before adding any new material making sure to check the depth. Always pull the mulch back a few inches so the base of the trunk and the root crown are exposed.
Remember, proper mulching is beneficial to tree health. Never mound mulch “volcano style” around landscape plantings and always use good organic mulch.
Certified Master Gardener