Volcano Mulching Harmful

Mulch Piled Up Around Tree

Piling up mulch around trees or shrubs, called “volcano mulching”, is a bad practice and is killing them. Perhaps you’ve seen a neighbor or a professional landscaper doing it, and assumed that it must be alright. It’s not!

The deep mulch pile smothers the natural buttress flair of the trunk which breathes and absorbs air for the rootsystem. The sugary sap underneath the thin bark skin is a food source for harmful insects which overwinter in the mulch piled around the bark. It also becomes a haven for critters, particularly rabbits and field mice. 

Organic-based mulches aid to conserve soil moisture, moderate soil temperature extremes and reduce competition from weeds. It also keeps mowers and string weeders (“weed wackers”) away from potentially damaging the tree trunk.

Mulch depth is recommended at 2-3 inches and is distributed around the tree in the form of a donut. The bulk of the mulch should lay 3 or more inches away from the trunk and taper off near the tree’s dripline (outer extent of branches). Excessive depth of the mulch also promotes shallow rooting by reducing oxygen to the roots. Trees become more susceptible to prolonged periods of drought.

Organic mulches include pine bark, hardwood bark, chopped leaves, pine needles, and composted grass clippings.

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