Garden mulch basics, including 7 problems caused by too much

View full sizeTHE OREGONIANMulching is one of the most beneficial ways to keep trees and other plants healthy. But over-mulching can be one of the worst landscaping mistakes you can make, causing significant damage to trees and other plants.

Spread mulch only 2 to 4 inches deep to help maintain soil moisture, control weeds, improve soil structure and inhibit certain plant diseases.

Too much mulch, in a deep layer or piled high against tree trunks, can cause gardening headaches, including:

*excess moisture in the root zone leading to plant stress and root rot;

*insect and disease problems;

*micronutrient deficiency or toxicity;

*weed growth;

*smelly planting beds, caused by anaerobic conditions and “sour” mulch;

*and habitat creation for rodents that chew bark and girdle trees.

 
Mulching basics

For well-drained sites, apply a 2 to 4-inch layer of mulch. If drainage problems exist, use a thinner layer.

If mulch is present, check the depth. Do not add more if the depth exceeds 4 inches. Instead, rake the old mulch to break up any matted layers and refresh the appearance.

Avoid placing mulch against tree trunks.

If mulch is already piled against stems or tree trunks, pull it back several inches so that the base of the trunk and the root crown are exposed.

Mulch out to the tree’s drip line or beyond if possible.

Most commonly available mulches work well in most landscapes. Some plants may benefit from the use of a slightly acidifying mulch, such as pine bark.

Organic mulches are preferable for their soil-enhancing properties. Be sure mulch is well-aerated and composted to avoid sour smells.
 
— Homes Gardens of the Northwest staff

If you want to automatically receive a free daily homes and gardens tip, sign up at OregonLive.com’s newsletters subscription site.