Dr. Gouin's Bay Gardener

Too Mulch of a Good Thing
Part 3: Death by Competition

Today’s home gardeners seem to feel that only mulches made from wood or such wood waste as barks are worthy of being called mulches. They also seem to like only mulch that’s dark brown, nearly black or scarlet red. Those tastes are reflected in the names of commonly marketed mulches: Double Shredded Hardwood Bark, Milled Pine Bark, Pine Bark Nuggets, Big Red, Big Blue.

Mulches colored red, blue, yellow or brown should not be used around shallow-rooted trees, shrubs, perennials and annuals. These mulches are made from ground pallets and demolition wood. When applied to the soil, they deplete nutrients from the top three to four inches of soil, where shallow-rooted plants anchor. The raw wood from which these mulches are made is a rich source of food for bacteria and fungi. To obtain their food, microorganisms rob the soil of nutrients. They obtain nutrients from the soil more effectively than the roots of plants.

Use colored mulches and your plants will become stunted, develop yellow-green foliage and often die. By the time these symptoms appear, it is typically too late to correct the problem by applying fertilizers.

Use colored mulches only in limited amounts around deep-rooted species and for pathways where you want to starve weeds.

Q When is the best time to mulch the root collar of trees and shrubs?

–Bob Resnik

A Mulching the base of trees and shrubs is a waste of time because they do not need protection. Mother Nature does not do it in the forest. Matter of fact, mounding mulch around the base of trees and shrubs is not only ugly but also promotes invasion from the clear-winged borer.

Professor Emeritus Francis Gouin retired from the University of Maryland, where he was the state’s extension specialist in ornamental horticulture. Follow his column of practical gardening and plant advice every week, only in Bay Weekly. Ask Dr. Gouin your questions at [email protected].