About a year ago, I wrote about the subject of improper use of mulch around the base of trees. Since that time it appears that in some ways the problem has gotten worse, so I’ll write about it again, hopefully reaching an audience that is more caring about tree culture.
To start, I should say that the people responsible for the care of trees in West Windsor’s parks and the Rogers Arboretum really do know what they are doing. In many cases this means that there is little or no mulch, because for mature trees it is not as necessary as it is with a newly planted tree. There are many examples of mature and very healthy trees in Community Park. I visit the park frequently and have yet to see an unhealthy tree.
If you see a tree in town that looks to be in bad shape, it’s probably on private property — including along some roads, which are maintained by homeowners’ associations, not the township.
Once a tree begins to mature and achieve equilibrium with its surroundings, making changes like adding more mulch is unnecessary unless there is a problem, say, with the nearby surroundings. If that means there is a lawn that must be mowed periodically, it is a good idea to have a thin bed of mulch surrounding the tree so the mowers don’t run into the trunk.
But for mature trees, the lawn frequently doesn’t grow very close to the tree anyway, so mowing doesn’t involve getting too close.
Depending on the tree species, the main bark-covered roots may spread out above ground. Mulch in the area of such roots can be beneficial in the retention of moisture, but it should be realized that a heavy rain could wash such mulch away if the layer is too thick. And actually covering bark on any part of the tree with mulch is not a good idea. Another often-claimed need for mulch is that it keeps string trimmers from damaging the bark. That claim is simply an example of careless use of the trimmers.
Another important factor in the mulch discussion is the type of mulch to use. The finely ground black mulch that one sees so often — especially at commercial sites — is not the kind to use around trees. The best kind for trees is wood chips or small pieces of tree bark. A layer of this mulch should not exceed four or five inches in depth and should be spread on the ground about as far out as the branches extend overhead.
Of course, if you want to plant ground cover like myrtle or flowering bulbs in that area, that is certainly a good way to make an attractive setting. But make sure that in cultivating the other plants you don’t damage the tree roots. From personal experience with many such situations, that’s not hard to do.
Older trees — say more than 25 years old — have demonstrated that they are adaptable to their surroundings, even if those surroundings are not ideal. Look at all the trees growing to maturity along sidewalks, for example, in the Princeton Junction area, or along the sidewalks anywhere in Princeton. Especially in Princeton, there are hundreds of century-old trees surrounded by paving that are as healthy as trees can be. They find their needed moisture either far below the pavement or beyond the pavement’s lateral extent. Surrounding these trees now with mulch in any amount would be pointless.
The same goes for mature trees surrounded by lawn, say, like those on the university campus or on our school grounds. Again, the most important time that mulch is useful is when a newly planted young tree needs help getting established after transplanting. And even then the amount of mulch needed is not very much: up to four or five inches at most and never touching the bark.
Think of proper mulch application in the form of a donut on the ground, with the outer diameter extending to the dripline. For mature trees this might be as far as 12 feet, depending on the nature of the surrounding territory. Obviously, many trees grow in areas where there are other trees, buildings, or parking lots closer that 12 feet away.
As long ago as 2002, the Division of Parks and Forestry of the New Jersey Department of Environmental Protection was aware of the problem of improper use of mulch around trees. It published a pamphlet titled “Volcanoes Killing Trees in New Jersey.” It referred, of course, to the large piles of mulch that were being placed around the trunks of trees so as to resemble a volcano. The pamphlet was also supported by the New Jersey Shade Tree Federation. Similar information has been published by the Arbor Day Foundation. An updated version of the NJDEP information is available through its website.
In view of so many mulch volcano situations at commercial sites in West Windsor and Plainsboro it’s not surprising that some homeowners have been duped into asking their landscape services to emulate what they see, say, at the Southfield Retail Center. At that location, there is a mix of mulch use — some good, some bad. On the islands in the parking lot, most of the planting —including trees — has avoided the over-use of mulch.
But on the lawn area bordering Route 571, the mulch volcanoes are huge. But since they have been there for a few years, care must be taken if they are ever going to be removed. Removal must be done gradually, since sudden removal can in itself be damaging. The NJDEP pamphlet suggests resources for advice on removal.
Although the best time for spring planting of trees has now passed, it would be good to remember that correct mulching is still very important. Both the U.S. Department of Agriculture and the New Jersey DEP have been publishing warnings about improper use of mulch for many years. Check out their websites for the best way to apply mulch and take good care of your trees.
