What is a Mulch Volcano?

Red, brown, black, shredded, mini-chunk, bark, cypress, pine-straw, rocks, etc. There are a ton of mulch options and varieties that are commercially available and can really set your landscape off with contrast and a uniform appearance. 

Not only does mulch look good, it also has benefits like soil moisture moderation, weed control, erosion prevention, and adds organic matter to the soil.

Trees also can benefit from mulch. Mulch provides a more consistent environment for root absorption and elongation and creates a place for beneficial fungus.

Mulch volcanos are a common yet surprisingly harmful mulch practice to your woody plants and trees! It describes mulch being mounded up to the base of the tree, with the plant at the highest point erupting from a mountain of woody debris.

In the wrong spot, decaying and wet organic matter will cause long term tree problems, even death.

The lower trunk of woody shrubs and trees are not designed to stay moist which is what a mulch volcano is doing. The bark can eventually rot away, exposing the living cambium underneath and inviting problems like buttress decay, parasitic fungi, and stem girdling roots. It's kind of like if you kept on a pair of wet shoes and socks for months or years at a time!

I’ve personally seen mulch volcanos piled 2 feet up the trunk of a tree! I've also seen many tree failures that were a direct result from years of bad mulching habits.

And yet, the practice continues to happen, often with good intent. For some reason, the harmful trend of piling rotting wood onto a living tree just “makes sense” to some people. I suspect it comes from gardening. Some vegetables like tomatoes are ready and capable of sending out adventitious roots from anywhere along the stem and are commonly planted in a mound.

The practice has been condemned for many years. Landscape conventions, garden shows, tree care companies and more have been crying, “stop the mulch volcanos” but the message just seems too slow to get out.

I was driving past a local gas station just the other day and saw some hardworking landscapers freshening the mulch around a commercial property and piling up mulch high onto the tree trunks.

It's a shame because it's not just bad for the trees- it's bad for the tree owners! Replanting a landscape tree can cost hundreds of dollars, not to mention the cost of the removal, stump grinding, and of course the wasted cost of the mulch and install fees. 

If you have a tree on your property that has mulch, leaves, or other debris piled up around the trunk, remove the debris as soon as possible and allow the area to dry out before inspecting for long term damage. 

If decay is found, consider consulting with an arborist to determine what options there are.