Mulch volcanoes around trees - Ask Extension
Thank you for your recent advice regarding my ailing trees. Your insights were highly informative, and I gained valuable knowledge. I now understand t...
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Mulch volcanoes around trees #867905
Asked May 10, 2024, 2:36 PM EDT
Thank you for your recent advice regarding my ailing trees. Your insights were highly informative, and I gained valuable knowledge. I now understand the detrimental effects of mulch volcanoes on trees, which I previously was unaware of. Upon further observation, I noticed that the trees in our community are surrounded by these mulch volcanoes (see picture attached). I have reached out to the landscaping company responsible for tree maintenance, and this was their response:
“The trees do not have any excess of mulch. They look the way they do because when they were initially planted, they were planted on a mound of dirt. The trees will be fine this year but we would definitely recommend, and had planned to make you aware of this, removing dirt from the tree pits during next year’s spring cleanup.”
Do you have any advice as a tree expert?
Harford County Maryland
Expert Response
Without seeing them in person, it's hard to say, but our impression is that they're still covered in too much soil and/or mulch. While perhaps not visible from the angle of the photos, in person, the root flare should be visible at the soil surface and not covered by anything, which does not appear to be the case here. Granted, younger trees won't have an obvious flaring of the trunk base at that point, for which the feature is named, but the junction where roots connect with the trunk is still the location that should lie just at the soil surface or even very slightly above.
Regarding the "mound of dirt"...we also don't understand why the installer would have put them above-grade (is it on a steep hill, where they couldn't plant the root ball level?), since root balls should be planted in a hole only as deep as the root ball itself, not shallower or deeper. (The risk of soil subsiding and sinking the root ball over time isn't very high if the soil underneath the root ball wasn't amended or disturbed, which it generally is not advised to be.) We're not clear on what "tree pits" they are describing; soil (and mulch) around a planted tree should be as level as possible (slope notwithstanding, if it's on a hill).
Our sense from the photos is that the trees are either set too high in the ground (if the soil is indeed mounded up), or over-mulched or planted too deeply, but we can't be certain. While these likely won't have any immediate impacts on tree health, over the long term, it can affect drought tolerance (if too high) and root oxygen access (if too low or buried), and/or promote the formation of girdling roots.
Miri
Regarding the "mound of dirt"...we also don't understand why the installer would have put them above-grade (is it on a steep hill, where they couldn't plant the root ball level?), since root balls should be planted in a hole only as deep as the root ball itself, not shallower or deeper. (The risk of soil subsiding and sinking the root ball over time isn't very high if the soil underneath the root ball wasn't amended or disturbed, which it generally is not advised to be.) We're not clear on what "tree pits" they are describing; soil (and mulch) around a planted tree should be as level as possible (slope notwithstanding, if it's on a hill).
Our sense from the photos is that the trees are either set too high in the ground (if the soil is indeed mounded up), or over-mulched or planted too deeply, but we can't be certain. While these likely won't have any immediate impacts on tree health, over the long term, it can affect drought tolerance (if too high) and root oxygen access (if too low or buried), and/or promote the formation of girdling roots.
Miri
