You can over mulch. Over-mulching is a serious problem responsible for the decline and death of many shallow rooted shrubs as well as large coniferous and deciduous trees.
We have long been aware of the importance of not placing excessive amounts of soil over the roots of established trees and shrubs.
However, we sometimes fail to understand that excessive use of mulch around shallow rooted plants has the same detrimental effect. Heavy and repeated applications of mulch around established azaleas, rhododendrons, mountain laurel, leucothoe, andromeda, boxwoods, hollies, yews, camellias, etc. suffocates their roots.
If the species is able to root readily, it will often initiate new roots from the stems into the mulch, but produce little top growth.
Shallow rooted plants growing on sand soils appear to tolerate more mulching than similar plants growing on heavy soils, but even they eventually succumb to suffocation.
Death to plants from over-mulching is slow. There is generally a gradual decline in the plant vigor. The annual rate of growth becomes less each year and the leaves do not grow to mature size.
Symptoms of iron chlorosis on the newly emerging leaves appear in late spring and late summer.
Approximately a year before the plants die, the new growth exhibits a severe iron chlorosis and there is often considerable winter die-back of branches.
There is a generally little response to foliar application of chelated iron or fertilizers.
During this late stage of decline, there is little chance for recovery and the plants become susceptible to attack by insects and diseases.
Boxwood decline can often be attributed to over-mulching. Simply removing the mulch from around the plants exhibiting early symptoms of decline has resulted in total recovery.
Many coniferous and hardwood trees are killed because mulch is piled high around the stems.
Organisms that cause stem rots thrive in the cool moist environment of heavy mulch. Most species of spruce appear to be especially susceptible to injury from mulch piled around their stems.
One to two inches of mulch applied every 2 to 3 years is adequate to keep the soil cool, reduce water lost by evaporation, give the landscape a neat appearance and to allow easy penetration of water into the soil.
Shallow raking of existing mulch will give the landscape planting that freshly mulched appearance.
Removing old mulch and replacing with new is also an option.
Mulches should not be used exclusively to control weeds. Organic mulches decompose and enrich the soil, making conditions favorable for seeds germination.
Weeds in landscape plantings should be controlled mechanically by hand weeding or with pre-and/or postemergence herbicides.
Clark Beusse is the Dawson County extension agent. For more information, call (706) 265-2442.