How To Mulch Trees – Don’t Make A Mulch Volcano!

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An important aspect to maintenance around trees is mulching. Mulching trees provides an array of benefit to the tree, provided it is done properly. When a tree is planted or an existing tree is thriving and growing for many years, it is important that the base of the trunk of the tree is exposed and flares out. We call this basal root flare. This is the transition area between the trunk (above ground growing parts of the tree) and the root system (below ground growing areas.) The root flare needs to be exposed and is the common condition for existing trees and thriving mature trees.

Mulch comes into to play when a new tree is planted to keep its root system covered, and to dress out a mature tree to improve its look aesthetically. Mulching does a variety of things, it helps hold nutrients in the soil so not lost to the atmosphere(particularly important on young and new trees), it prevents weeds from emerging or at least hinders them, it holds moisture on the soil line and keeps young trees and plants properly hydrated, it prevents compaction to the soil which is bad for root development, its aesthetically pleasing (coming in numerous colors and styles of bark), and it reduces the amount of freezing and cold exposure to the root system by insulating the ground. It’s important to mulch for these reasons and many others, but there are various effects to avoid when mulching.

One particular problem that is running rampant is the often seen MULCH VOLCANO! See picture below. A mulch volcano is a large buildup of mulch, intentionally placed around the root flare of a tree and often times up its trunk as well. This is very bad for the tree. This is often seen in malls, large box store plazas and commercial areas. I think this is done in effort to perhaps make the trees look pleasing and bring attention the amount of mulch placed around the tree. I also think it’s done to suffocate weeds so maintenance is reduced over the summer months. I believe too, it is also done because there is no quality control or supervision and mulch is being spread at an alarming(overbilled) rate which ultimately is unhealthy for the tree’s longevity and will kill it.

Mulch volcanos begin as a tree is planted and it needs ample coverage to protect its young roots and base. However at the beginning most laborers are placing too mulch around the flare and trunk creating the first layer of buildup. The next season, more mulch is placed around the trees flare and trunk. The next season again and again and again. Some mulch will break down, blow away or get pushed around from season to season, but mulch will mat itself together forming a woven barrier and the tree is defenseless. The reason the much volcano is bad is due to the constricting layer of mulch buried up around the flare and trunk. These areas naturally need to be exposed. If you walk in the woods and look around at the trees, you will almost always see the flare and exposed trunk and in some cases wood tree roots living ABOVE the forest floor….naturally. This is the natural manner with which to be concerned with when mulching. When mulch is buried up the trees trunk and around the flare, the mulch collects moisture and then it proceeds to rot around these parts of the tree. When the rot sets into the trunk and flare, the bark and protective tissue of the trees become weakened and exposed. Once the bark goes away, the important internal components of the tree become exposed. This is like ripping your skin off. At that point, insects, disease, decay, malformation and decline all move in and slowly kill the tree. Trees have a natural ability to survive like people or animals, but it’s this mulch buried up the trunk that immediately sets the tree into a position of deterioration before it can really get a healthy chance to evolve and mature. Trees in shopping plaza already have a tough life, with shopping carts, snowplows, cars, small root zones and growing areas, parking lot exposure, high heat, drought, vandalism, neglect, malnutrition, wind, etc. Prevent one of the worst problems by mulching properly and avoid the mulch volcano.

When mulching a tree place only a thin layer of mulch around its flare or none at all. Feel around that area of the tree and you will see that it’s naturally woody and composed of roots anyway, so leave it be. Put NO MULCH around the flare or the trunk ever when mulching in your strip mall or even around the house. The same rule also applies to plants, woody shrubs, perennials etc. And the best thing you can also do is report mulch volcanoes to the management company and educate the staff and landscapers. GOOD LUCK!

-Bruce F. Lindsay
B.S. Horticulture
Milford Patch Article

young ornamental tree with a mulch base

Another mulch volcano. Yes this may look nice, but it is at the detriment of your tree’s health!

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