Volcano mulching is the nic-name for the VERY BAD practice of installing mulch literally up the trunks of trees thereby creating what looks like a “Volcano” of mulch from which the tree trunk is erupting. (see below for a partial list of reasons WHY this is BAD).
There are many reasons why "Volcano Mulching" is detrimental to the long term health of the tree, here are a few:
- Trunk Rot - Bark tissue is different from root tissue and not "designed" to be continually moist or submerged. Covering the trunk with mulch will keep the bark moist and eventually the bark will decay, this will further lead to insects and disease feeding on the decayed tissue and eventually the tree (or shrub) will die.
- Suffocate/ Girdle the tree – Tree roots collect oxygen for the tree, the surface roots are now smothered by too much mulch so the distressed tree will send out little capillary roots into the mulch. Unfortunately these little roots are now above the soil line and subject to summer heat and winter frost damage and if they manage to survive these afflictions the roots grow larger encircling the thee trunk and eventually girdling or choking itself.
- Thirsty Tree - In the image above the slope is pushing water away from the tree before it has a chance to absorb into the ground. And the mulch is so thick, it is highly unlikely that rainwater could penetrate that mound and reach the tree roots where the water is needed.
- Home for pests – Mice, voles, insects etc. now have a comfortable home right next to your tree trunk and they can feast away undetected. Poor tree!
Did I mention that this is a BAD practice?
Proper application of mulch can be helpful, especially when establishing new plants:
Keep Soil Cooler in heat of summer
Reduce water evaporation
Reduce soil erosion from wind (and water runoff)
Proper application of mulch should not submerge the tree flange let alone cover the bark. And it should not be deeper than 2" to 4" (at the most!).