Mulching around trees is an excellent thing to do. But “mulch volcanoes” are problematic for many reasons. Learn how to properly mulch around your trees to make sure they will be happy and healthy for years.
You might already be mulching around your trees to make mowing easier. Or you might have seen mounds of mulch around trees in your neighborhood and are wondering if you should be doing the same thing.
As with anything, there are pros and cons to mulching around trees, but in my experience working alongside certified arborists and tree experts, it’s usually a good thing to do.
Mulching around trees to prevent damage to bark
Mulching prevents the need for lawnmowers and weed-wackers to get near trees. Why is this important? Because these tools can nick the tree bark and cause wounds. Obviously, this is not a good situation and yet many folks (incuding professional landscape contractors) do not realize this is a problem.
According to Bartlett Tree Experts, bark wounds can damage the vascular tissue of the tree and open it up to decay and infections. This can be deadly.
Ideally, a mulch circle should extend the distance of the tree’s canopy. But even a smaller circle is helpful to keep lawn turf and weeds from growing around the base of the tree and requiring machine maintenance.
Mulching to eliminate competition from lawn
You might not know that usually a tree’s feeder roots reside in the top 12″ of soil and extend far beyond the tree’s canopy. These are the roots that absorb the water and nutrients the tree needs to sustain life. But when turf (lawn grass) grows in this area, it absorbs water and nutrients, especially nitrogen, for its own needs.
If you can imagine a tree growing in a natural setting, there will usually be decaying leaves under the tree or an understory of plants compatible with the tree, not lawn. So, mulching under trees in the landscape provides a setting similar to nature.
As a bonus, if you allow a tree’s fallen leaves to remain on the ground in the mulched bed in fall and winter, those leaves will break down and will be recycled by the tree as nutrients.
Mulching trees to create visual interest in the landscape
Personally, I think using undyed shredded bark mulch is best, because it looks the most natural. I also use a neutral-tone cedar mulch just because it is so easy to handle (it is quite light).
Red and black mulches can appear unnatural in the landscape, but some folks enjoy the contrast of color.
Stone or rubber mulch is not a good idea to place around trees, because it does not break down to add organic matter in the soil. The types of mulches are also a hassle to maintain.
Be aware of the artillery fungus (Sphaerobulus stellatus), which can live in mulch. If the conditions are right, it can do serious damage to your home’s siding or paint. Even your car can sustain damage from the tiny black spores launched by this strange organism, sometimes up to 20′ feet away!
Mulching around trees correctly
There are good reasons for putting mulch around trees, but there are also hazards involved if the process is not done properly. Quite simply, improper application of mulch can cause the tree to suffer a slow death.
Add around 3″ of mulch after you remove weeds and turf. The removal process can happen in any number of ways, but it is truly worth a phone call to your local tree specialist to come out and advise you. Every tree and every landscape are different.
Know that it has to be done with great care, so as not to disturb the tree’s delicate feeder roots, as mentioned previously.
The most important thing is not to let any mulch touch the tree itself.
Alternatively, you can remove turf grass and plant groundcover or understory plants instead, which is generally how trees grow in the forest.
Avoiding mulch volcanoes
When you see a pile of mulch mounted up against the base of a tree, it’s often called a “mulch volcano.” Do not do this!
Mulch volcanoes do the following:
- Shelter pests like voles, who chew on the tree roots.
- Harbor pathogens.
- Cause rot.
- Encourage root girdling (roots encircle the tree and eventually cut off its vascular system).
- Act almost like a compost pile and heat up the base of the tree, causing tissue decay.
- Provide a medium for roots to grow above ground, which then can dry out during hot spells, and damage the tree.
The flare of the tree (the place where the roots begin to flare out from the tree’s trunk and go underground) roots should always remain visible and free of mulch.
Professional contractors often create mulch volcanoes because their customers like them. Or perhaps they do not want to take the time to remove last year’s mulch, so it continues to build up. Many people simply imagine a mound of mulch to be a good thing, as a way to protect the tree, not meaning to do any harm.
It’s easy to get it right if you keep nature in mind. Take a walk in the woods, and you can observe how trees grow in nature and take your cues from that.
Check out The Cornell Guide for Planting and Maintaining Trees and Shrubs for a comprehensive guide to caring for trees in your landscape.
This post appeared previously on The Simple Landscape blog.
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