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Mulch Mania

Oh the harm it causes!

In 1976, I wrote “Over-Mulching, A National Disaster” for a national trade journal. Nasty letters came from as far as Oregon and California. Forty years later, over-mulching has become a monkey-see-monkey-do calamity.
     Earlier this spring, I spent several days diagnosing plant problems for several landscape architects. In all but one, the problems were caused by excessive use of nutrient-robbing mulches.
    In several instances, well-established plantings of pachysandra were being suffocated by excessive mulch or starved by mulches containing raw wood. Where raw wood was applied around pachysandra, the plants were yellow green and the vegetation sparse. In the areas where four inches or more of mulch was applied, the pachysandra was dead and the stems rotten. 
    In one landscape, several hundreds of square feet of what was once a well established planting of English ivy was killed after having been mulched with Big Red. About three inches had been applied last year, follow by another application this year. I am frequently asked to recommend an herbicide for killing English ivy; from now on I will recommend a heavy mulching with Big Red. Guaranteed to give 100 percent control, organically.
    I saw azaleas with sparse distribution of small purple leaves and struggling in what appeared to be two to four inches of shredded hardwood bark. Soil tests indicated in excess of 300 pounds of manganese. Any level in excess of 80 pounds per acre is considered toxic to the roots of plants. It’s clear from the soil test results that shredded hardwood bark had been applied repeatedly for several years. Since the property owner had hired several yard maintenance firms over the years, she was not aware of what kind of mulch had been applied.
    In one yard I examined a large planting of boxwood with severe symptoms of decline. Digging around the base of the plants, I saw that they had been mulched several times. Over the years I have seen numerous once-healthy and hardy boxwoods killed by mulch. Boxwoods are shallow-rooted plants and should never be mulched. They are drought tolerant, and enzymes emitted by the roots and leaves prevent many weed species from growing around them.
    Most of the landscape maintenance companies were blaming poor drainage for decline or death. However, as I walked on the lawns adjoining these plantings and in the plantings, I saw and felt no symptoms of poor drainage. I augured holes in these areas and found the soil to be well drained.
    The only landscape where I did not see mulch problems was in a yard where water coming from a newly installed copper roof had flowed. Here, the decline in growth and the loss of plants was due to copper toxicity. I could easily follow the flow of water from the downspouts and areas where the water pooled. The solution to this problem was to divert the water away from the plants until the surface of the copper sheeting oxidizes to a brown or gray-green color.
    More on mulch next week …


Ask Dr. Gouin your questions at DR.FRGouin@gmail.com. Please include your name and address.