I see increasing evidence of volcano type mounds of mulch being placed around tree of all sizes and ages. I would appreciate having your opinion on the subject.
The practice of placing mulch in “volcano” style mounds (i.e., piled up against the trunk of the tree) is not considered best practice by organizations such as the Toronto Master Gardeners, the City of Toronto, LEAF (Local Enhancement and Appreciation of Forests, which serves Toronto’s urban forests), or (OMAFRA) Ontario Ministry of Agriculture, Food, and Rural Affairs . Instead, two to three inches of mulch should be placed in a “doughnut” or ring-shaped layer around the tree, making sure that it is kept away from the trunk of the tree itself. Mounding mulch against the trunk of a tree is not recommended as mulch retains moisture and can promote rotting of the tree bark. Newly planted trees by the City of Toronto’s Urban Forestry Department use the ring-shaped style of mulching. Mulching established trees in this way not only helps to preserve soil moisture, but it also prevents compaction of soil around the tree, reduces weed competition, protects the trunk from injury by lawn mowers and other equipment, and helps improve soil quality. In addition, applying a layer of mulch aids in controlling temperature fluctuation and the freeze-thaw cycle, particularly helpful in protecting newly planted trees.
The Master Gardeners of Ontario is an umbrella volunteer organization which is committed to best horticultural practices, as are all its local members including the Toronto Master Gardeners. The City of Toronto and the Toronto Master Gardeners have partnered to prepare a series of guides to organic gardening which are available on our website here, as is our own guide to the care of trees. I hope this is helpful.