Volume 13, Issue25 ~ June 23 -29 , 2005

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Dr. Gouin's Bay Gardener

Too Mulch of a Good Thing
Part 5: Plant Death by Drought from Too Much Mulch

Over the years, I have seen many perennial and annuals in heavily mulched gardens die because the layer of mulch was so thick that water never penetrated to the soil. This problem is most common during dry years. A thick layer of partially decomposed wood-waste mulch, resulting from repeated applications without adequate soil incorporation, becomes like a sponge. If there is limited natural precipitation and the gardens are only hand watered, it is likely that most of the water will remain in the mulch layer. I have seen this mostly in gardens where the mulch layer is four to six inches deep.

Furthermore, hand watering of lawn and gardens is not recommended. If you don’t have the patience to spend hours watering by hand, the only proper way of watering a garden or lawn is either by overhead sprinkler or with soaker hoses.

Another problem associated with the accumulation of thick layers of mulch is the death of mulch-growing roots of trees and shrubs in long drought. During wet years, the trees and shrubs grew their roots into the thick mulch layer because the existing roots were asphyxiated by wet soil conditions caused by excess mulch. Since the roots of those trees and shrubs were mostly in the mulch, the roots die from the lack of water during extended drought. Layers of mulch cannot retain as much moisture as soil does, and mulches tend to dry out more rapidly than soil because of differences in texture. Symptoms of this fate — this was a severe problem the summer of 2001 — are early summer defoliation and death of the new growth at the ends of the branches.

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].

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