Mulch is an excellent addition to any tree or garden bed when used appropriately. Unfortunately, it is all too common in our urban environment to see mulch excessively piled up against the trunk of the tree, commonly referred to as volcano mulching. This practice is detrimental to the tree and in all cases, will lead to its early demise if left unattended to. Combined with this improper mulching practice also comes improper planting depth as well as lack of exposing the root flare of the tree prior to planting.

If you drive through any commercial parking lot, it is almost impossible to not see a tree that is volcano mulched. Piling the much is the the culprit here, but it is often preluded due to two other factors. The first is the planting depth of the tree often is too shallow. This results in a portion of the root ball sitting above grade and causing a slope as the mulch is applied. Second is that the root flare of the tree was never exposed prior to planting. At the time of the tree being dug in the nursery, it isn’t uncommon that the root ball is too deep for the tree and it comes with the root flare already covered up. To address this issue, it is important that prior to planting the tree, you dig out the soil surrounding the trunk until you find the root flare. Exposing the root flare and having the top of the root ball being even with the grade of the ground will eliminate the risk of inadvertent volcano mulching. When applying the mulch, simply have the mulch be level with the ground, about 6″ away from the trunk of the tree and about a maximum depth of 3″. As you apply new mulch over the years, pull away the old mulch if need be. Ideally, majority of the old mulch breaks down and incorporates into the soil.

So, what do you do if the tree is already in the ground and volcano mulched, non-exposed root flare and likely too shallow or too deeply planted? There is a treatment that an ISA Certified Arborist can recommend and conduct that will help reduce the stress to the tree, it is called a root collar excavation. This treatment is most often done using an air spade, a tool that blows compressed air to break up the soil and mulch surrounding the tree. The arborist will excavate the soil and mulch from around the trunk of the tree until they find the root flare. As the soil is excavated, the arborist will inspect and assess the condition of the root collar, identify and expose the root flare zone and look for any roots that are referred to as stem girdling roots or SGR’s. SGR’s are roots that have grown across or around the trunk of the tree, which will stress the tree and put the tree into decline or reduced growth. These girdling roots can be fatal to the tree in the long run. These roots can be pruned out at that time of the root collar excavation, but an arborist will be best to make the decision as to if they can or not, depending how much they may have enveloped the trunk. A root collar excavation is ultimately an exploratory treatment that will address problems that can be observed above ground, as well as identify issues that exist below ground, including the opportunity to assess the soil and potentially take a sample for further analysis if need be.

Following the excavation, the soil can then be put back in place, often with added amendments such as a mixture of soil and leaf mulch or other beneficial additives. The mulch would then be reapplied in the appropriate manner, level with the ground, about 6″ away from the trunk of the tree and at a maximum depth of 6″. The tree can recover and prosper following this type of treatment, and unfortunately there are many trees in our urban forest in need of this treatment.

To avoid this issue with future trees planted, it is critical that those who plant trees are aware of these potential issues and plant the tree properly from the beginning, along with proper mulch application. Continual training, education and practice in these areas of arboriculture will ultimately lead to healthier, more vigorous and ultimately maximize the benefits that trees provide in our urban forest. Help us lead the way in stomping out volcano mulch and thank you for doing your part to spread the word!

Say NO to volca-NO mulching!