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Don’t Let Spring Fever Erupt into Mulch Volcanoes


ST. CHARLES, Ill. – Symptoms of Spring Fever may be heightened thanks to the long winter and the mid-April snow. Many homeowners are itching to get in the yard, and one of the first tasks tackled is mulching. But do we do it properly?

“There are many benefits when it is done right,” said Richard Hentschel, horticulture educator with University of Illinois Extension. “Mulching trees and shrubs controls weeds, conserves moisture and lessens the time in the yard trimming after you are done mowing the lawn.”

In addition, mulch provides root system protection from seasonal changes in temperatures, cold or hot. For a young tree, it also will keep the lawn mower and string trimmer from damaging the trunk, and on our older trees, the mulch ring lessens the handwork needed to maintain the yard. Plus, it makes the yard look neater.

That said, Hentschel warns that there is a correct technique to mulching, and it does not resemble a volcano.

“As you drive around your town or neighborhood, you may see trees mulched high up the trunk with the pile angling downward like a mountain,” he said. “This is called ‘volcano mulching,’ and you do not want to do it. There is not a single sound horticultural reference that will say volcano mulching is a good thing, yet it is quite common.”

So, what happens when we mulch the wrong way?

“Nothing at first. Damage occurs over time and later when the tree is suffering, we do not relate the volcano mulching to the tree’s symptoms,” he said.

“The trunk of the tree is designed by nature to be exposed to the elements, and that is why a tree trunk is covered in bark,” he explained. “The bark is a collection of dead cells that provide insulation to the more sensitive parts in the cambium layer. When mulch decomposes, it generates heat. This heat damages this important cambium layer, lessoning the trees ability to move water and needed nutrients up and down the tree.”

It also will cause the trunk to begin to decay, allowing pathogens to enter the tree. In addition, because the bark is now in the dark, some trees will even attempt to grow roots out into the mulch rather than into the soil where they belong.

The proper way to mulch is never to allow mulch to cover the bark by leaving a small ring around the trunk exposed down to the soil and mounding up the mulch three or four inches out and away from the tree trunk to the size of the ring appropriate for the tree size.

“Think donut, not volcano,” added Hentschel. “Plan on reapplying the mulch as the mulch ring decomposes. This will vary by type of mulch; some break down in a year, others will last two or more. Lastly, it is appropriate to freshen the ring by loosening the mulch with a garden rake, just don’t leave it rest on the soil to cake over.”


Source: Richard Hentschel, Extension Educator, Horticulture,

Pull date: July 15, 2019