I see many people in the neighborhood hire landscapers or do mulching around trees themselves. Without knowing it, this well intentioned act is often done incorrectly, which can be unhealthy for our neighborhood trees. Having the right amount of mulch is beneficial, while piling it too deep, can cause problems. Here's more information on how to do mulching correctly and keep trees healthier.
“Volcano Mulching,” a practice used by many landscape companies and some homeowners, is when a mulch ring 2-3 feet wide and over 4 inches deep is placed around trees. This practice is extremely harmful to the health of trees.
If your tree has been volcano mulched, use gloved hands to remove mulch from the base of the tree, exposing the root flare (the area where the roots turn out and away from the tree).
Do not use a rake or shovel, as this can damage delicate roots. If removing years of layered mulch by hand is too difficult, hire a tree care company that will use an air spade to do the job.
Mulching is one of the most beneficial things that you can do to keep your trees healthy. If done incorrectly, however, it can also lead to the death of your tree. Mulching increases soil organic matter, water-holding capacity and nutrient availability. It also acts as an insulator, buffering the soil from rapid temperature changes. It helps control weeds and protects the trees’ trunk from being hit by the lawn equipment.
Here's some helpful about mulching trees:
Make sure that mulch is pulled a few inches away from the base of the tree to expose the root flare, usually 4-6 inches. M
ulch should be applied approximately 4 inches deep in a donut-shaped ring. This will settle to a desirable two inches after a few rains, and is shallow enough to allow rain to reach the roots.
Mulch out away from the tree in a 4-5 foot diameter. Ideally, trees should be mulched to the drip line (below the farthest reaching branches). Consider mixing hardwood mulch with grass clippings, sawdust, pine needles, compost, and shredded leaves to increase porosity. Using a groundcover plant instead of mulch or grass is also a good choice. Check mulch levels annually. Trees often do not need to be mulched every year.
Piling mulch high around the base of the tree should be avoided. This causes damage to the bark due to constant moisture, diseases, termites, rodents, and fungus. It also causes rainwater to run off before it has a chance to soak into the root area.
Here's an example of volcano mulching where the roots are buried way too deep.
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| Mulch is about 1 foot deep against the trunk of the tree. |
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Another issue - the tree has outgrown the protective collar put
on when it was planted. These are intended to protect against
lawn mower wounds. If the tree has outgrown the collar to the
point where the collar has an open gap, please remove it. |
Mulch should not be piled higher than 4 inches from the ground. Doing so causes roots to migrate to the surface to “breathe” and access water exposing them to a variety of health risks.
Cypress mulch should be avoided. It is very water absorbent, reducing the amount of water that reaches the tree roots. The logging of cypress trees destroys cypress forests in the swamps of Florida and Georgia - a significant ecosystem in the region.
On a related note,
please don't build raised planter areas around the base of your trees. Similar to the deep mulch example in the paragraph above, burying tree roots under a planter bed causes them to migrate to the surface in search of oxygen. These roots will circle around inside the bed - a problem known as
root girdling. This can shorten the life of the tree.
Here's an example of what happens to your tree when you build a raised planter area around it. This is a medium sized maple tree that had a foot-high planter bed around it for years. After that was removed, this extreme example of root girdling was revealed. Much of the canopy is already dying. This tree could have had a much longer life, and it's likely to be dead within a few years.
Dyed mulch is less desirable. It is usually made from chemically-treated scrap lumber that can leach chemicals into the soil. The dye itself is also often made from synthetic chemicals. It's worth discussing this issue with your landscaper, or carefully considering your choices at the garden center if you're doing you're own mulching, to help your trees be as healthy as possible.
More information on volcano mulching and proper mulching techniques:
Mulch Volcanoes - University of Illinois Extension
https://extension.illinois.edu/gardenerscorner/issue_07/spring_05_11.cfm
The Pros and Cons of Mulch - University of Illinois Extension
https://web.extension.illinois.edu/state/newsdetail.cfm?NewsID=20691
Mulching Trees and Shrubs - The Morton Arboretum
https://www.mortonarb.org/trees-plants/tree-and-plant-advice/horticulture-care/mulching-trees-and-shrubs
Remember - donut shaped mulch rings with breathing room around tree trunks are healthier. Most landscapers don't know anything about tree health. If your landscaper is making mulch volcanoes, instruct them about the donut method. Tell them that the info comes from Morton Arboretum and University of Illinois and that it's available online if they have questions. You'll be doing your trees a favor, and it will be better for the trees they work around in other people's yards.
