Mulch Volcanoes Around Your Trees
Somewhere along the line it became common practice in the landscaping industry to plant trees too deeply, or to pile up mulch against the trunk after planting to create the “mulch volcano” we are all so used to seeing in our neighborhoods and urban landscapes. We honestly can’t tell you if there was initially some bad science behind this practice, or if it was purely aesthetic, but we can assure you this is not a good practice if you want to have long-lived healthy trees and avoid the expense of constantly trying to correct health issues with your tree or the costs of removal and replanting.
Why do arborists hate mulch volcanoes?
The problem with mulch when it is applied too deeply and/or piled up against the trunk is that this eliminates air flow and can suffocate your root system or root flare (base of the tree trunk), and cause too much moisture retention. This can then become a breeding ground for fungal and bacterial pathogens to develop. Stressed trees become increasingly susceptible to any number of pest and disease issues.
Additionally, as surface roots grow upward through the mulch searching for air, water, and nutrients, they can sometimes wrap around the trunk of the tree or other major roots and quite literally strangle the entire tree over time. These circling roots are called girdling roots, and can sometimes be pruned to correct this issue (along with mulch removal/root collar excavation) if the condition of the tree is not already too far in decline.
So how should my trees be mulched?
Don’t get us wrong, arborists love mulch (and we give it away for free)! We usually recommend unprocessed arborist wood chip mulch around the base of your tree (but not directly against the trunk), 2-4 inches deep at most.
This mulch provides natural slow-release fertilization to your tree, mimicking the breakdown of leaves and plant debris on the forest floor. The mulch also maintains soil moisture and can even help with weed suppression, reducing competition for nutrients around your tree’s root zone!
If you don’t mind the look of leaves, you could also achieve similar benefits at no cost simply by allowing your tree’s shed leaves to remain where they fall.
Other Keys to Healthy Saplings:
What other factors are important to consider if the goal is healthy saplings?
- Proper species and site selection. Will the species you’ve chosen have room to grow to full size in this location? Are the sun conditions correct? Is the species hardy to our growing zone?
- Specimen selection. Choosing a healthy sapling from the nursery without damage, root girdling, pests, or disease.
- Proper planting technique, along with proper mulching. Deer protection where necessary.
- Appropriate aftercare plan. In our opinion, the goal is to plant saplings which will become self-sufficient, resilient, low-maintenance mature trees in time. Believe it or not, under-watering is typically better than over-watering (we like deep infrequent watering over shallow frequent watering)! Watering should typically not be necessary after the first or second growing season (if at all).
