Mulch Volcanoes!

This is the time of year when you will start thinking about your landscape. One of the most common things to do with your landscape in the Spring is to clean out the debris that has accumulated in the mulch beds over the Winter and then spread a layer of fresh mulch. This is a great practice that has numerous benefits for your flowers, trees, and shrubs while also making your yard look fresh, clean, and ready for Spring. But as with all good things, moderation and a bit of knowledge are key for a proper application.

What’s the Deal?

So what could possibly be the problem with mulch? Briefly, too much of it. Why is too much mulch a problem?

For trees and shrubs, the problem arises when mulch is piled up around the woody stems of shrubs and the trunks of trees. The result is a mound of mulch that grows as it is piled up again, year after year until… the emergence of the dreaded MULCH VOLCANO! Okay, okay, this volcano doesn’t spew fire and noxious gases. In fact, it appears pretty mundane. But don’t let it fool you, because over time this humble mound of mulch can lead to the death of even the largest trees.

So how does a mulch volcano cause a tree to die? By simply raking a bit of mulch away from the surface we can begin to see the root of the problem. After a relatively short time, a tree that has been over-mulched will begin to fill up the inside of the volcano with roots. Yes, that’s right, the tree’s roots will grow upward!

This becomes a problem because as these roots grow they do not radiate outward, but instead begin to follow the circle of mulch around the trunk of the tree. This leads to a situation referred to as girdling roots. As the tree grows, the roots and the trunk both get bigger, and eventually, they start to push against one another. In this battle for space, the trunk of the tree becomes constricted. This constriction becomes worse with time and eventually, it begins to restrict the flow of nutrients from the roots to the canopy.

Another reason too much mulch can be a problem has to do with the moisture-holding ability of mulch. The trunk of the tree is NOT meant to be wet all the time, and since mulch is great at holding moisture, which helps the soil and roots, it can cause damage and decay to the actual trunk. This can lead to more trunk wounds, trunk and root decay, and even structure issues.

How to Spot Harm

You can tell if too much mulch is harming the tree in a few different ways. The first place to look is at the bottom of the tree where the trunk meets the earth. Ideally, your tree will have what is called a ‘root flare’ where the trunk widens out at the base. If your tree goes into the earth in a straight line like a telephone pole, or worse if the trunk gets smaller at the base, then there is a good chance there has been or currently has too much mulch around it. If the mulch is more than a few inches higher than the surrounding grade or comes up to the trunk of the tree at a steep angle, then you may have conditions that favor the formation of girdling roots. These signs may be a bit difficult to detect if the tree is small or if it is located in a large landscape bed.

The next place to look is at the leaves. Trees that are suffering from girdling roots or trunk decay will often have a washed-out or yellowish tint to their leaves. This is a result of the restricted nutrient flow up the trunk of the tree. The leaves simply can’t get what they need to thrive and it becomes more noticeable every year. Not all trees respond in the same way, however. Some trees may have green, healthy-looking leaves, but have thin spots around the canopy or dead twig tips.

If you suspect that your tree might have been over-mulched and is suffering from girdling roots it is important to fix the problem. This is done by pruning the girdling roots away from the trunk of the tree while at the same time lowering the height of the mulch to match the surrounding grade. This is easy to say, but in practice, it can be very labor-intensive and it must be done with care so that the trunk and root flare of the tree is not damaged. When considering what to do about a tree with mulch and root problems, consider that with each annual application of fresh mulch the issue will become worse. Early treatment is much more cost-effective and will produce better results, but even larger trees that have been living with mulch volcanoes for many years will still benefit from having their girdling roots pruned.

We’ve Got You Covered

At Joseph Tree, we have a toolbox of solutions for almost any problem that your trees and shrubs may be dealing with and we have had great success in correcting girdling roots and mulch volcanoes. Contact us today and we will have one of our certified arborists work with you to tailor a custom solution that fits your landscape.