I get lots of pictures of sick trees. Most of the time the first photo sent to me is a declining canopy. Maybe a picture of an ugly leaf. After all, that’s what we tend to notice first as our eyes occasionally gaze upward to the living behemoths that shade our parks, yards, and homes.
There is one thing I always request of a client before proceeding with any type of diagnosis of the ailing tree: A photo of the base of the trunk as it emerges from the ground. Why is this section of the tree so important? Because this is where I tend to find the majority of the problems in large shade trees.
If you walk in the forest or a park with older established trees, look at the base of the trunk. More than likely you will see the trunk flare out at the base. This is called the root flare. The important thing to note for trees is that roots are adapted to being buried in the soil, but the root flare and trunk must be above the soil line. If it looks like a telephone pole sticking out of the ground, the tree is planted too deep.
Please know, most trees are already planted too deep in their container at the time of purchase. Often you will need to gently excavate the top few inches of soil in the pot until you identify a distinct flare or the first structural root. Some species (notably evergreens) may not have a clear root flare as young trees. That’s when you identify that first structural root as your guide.
Planting a tree too deep does not equal immediate death. Few things kill a tree instantly besides a chainsaw. A tree planted too deep will have a shortened life span as the root flare and any portion of the buried trunk slowly succumb to rot. Instead of a 200-year-old oak, maybe it will last 10 to 20 years. Not bad for the average length of time Americans own a home, but not great considering the oak’s potential lifespan.
It is recommended to mulch young shade trees. I would argue large ones benefit from mulch too. It keeps the mowers and string trimmers away, reduces competition from turfgrass, and creates a defined space around the tree that has an aesthetic appeal. But how and what we mulch with can lead to a healthy tree or an ailing tree.
As a landscaper, I put tons (literally) of decorative gravel around trees as mulch. People like the look, it doesn’t decompose, and you can just hit any weeds with some weed killer. Sounds simple, from a designer’s point of view. But from a horticultural standpoint, rock mulch adds nothing to the health of the plant. It can even create conditions that make the area less hospitable to the tree. Even if the rock doesn’t decompose like wood mulch, it still settles into the soil and can become a nightmare if you ever need to remove the stuff. Some will place plastic underneath to prevent this. Which is another practice Extension does not recommend. Plastic under mulch restricts air and water to the tree roots below. Plus, don’t we already have enough plastic out in the world?
Arborist woodchips are a recommended type of mulch as these tend to be coarse and don’t pack down like some shredded wood mulches. These are often readily available in Illinois. Shredded wood mulch is not a bad option, and I use these when I can’t get my hands on arborist woodchips. Shredded fall leaves are also a favorite of mine, and I used these extensively at my former home.
Many times you can find recommendations to place landscape fabric as an underlayment beneath mulch. There is certainly merit to this strategy as this fabric can cut down on weeds growing through your mulch layer, at least for a few years. Over time the pores of the landscape fabric that permits water and air through can become clogged with fine silt material and become no better than having a sheet of impermeable plastic. Ripping out the non-functioning fabric can be quite the chore.
So is there a good material to use underneath mulch? Not really. Some gardeners will use cardboard, but that too can become hydrophilic and repel water. Newspaper can do the same, especially if there are too many layers. You’ll see many current Extension sources state to simply maintain an adequate mulch depth and pull any weeds that push through.
This is tough to stomach, personally, as I know all too well some weeds will easily grow through a layer of mulch. So you could mulch deeply (over six-inches deep) or place a few sheets of newsprint on the soil to restrict that first flush of weeds that often occur with soil disturbance. The thin layer of newsprint (avoid glossy paper) should decompose within a year and then it is up to the gardener to maintain that mulch layer. Preemergent herbicides may also be useful in establishing a mulched bed around a tree. Follow all pesticide label directions.
Another situation I often encounter is a tree, young or old, that is planted at the perfect height. The root flare is visible. The tree is healthy. The only thing to do is mulch the tree. What unfortunately happens too often is homeowners (and some landscapers) pile mulch up against the trunk of the tree. We call this volcano mulching and is akin to planting the tree too deep.
These trees with mulch mounded against the trunk create conditions that are favorable to rot and decay around the trunk. The recommended mulch technique is to mulch the root system, not the tree, at a 2- to 4-inch depth, going as wide as practical, and leaving a 2-inch gap between the mulch and the tree trunk.
Last but not least, a common issue at the base of tree trunks is girdling root. I wasn’t quite sure if girdling root deserved its own section as everything mentioned above promotes the development of girdling roots, but there are a few extras I can throw in here.
Tree roots should grow out from the trunk, but nursery-grown trees commonly develop girdling roots. This is due to being grown in plastic containers and when the young root encounters the impassable wall of the container, it turns and goes in a circle. To remedy this at planting, some will shave off the sides of the root ball. Essentially, turning the sphere-shaped root ball into a cube shape.
Another technique is root washing, where the root ball is rinsed and cleared of all the soil to reveal any circling roots. These problem roots are then pruned off. Depending on the tree, the top half may be very top-heavy with no soil anchoring to the roots. Staking may be necessary. I root washed some trees in 2019 and it was a lot of work. Instead of stakes tied to the trunk, I used 1x2 boards to pin down the root area that prevented the trees from toppling over while still allowing the trees to flex in the wind and build a solid trunk taper. The loss of roots can be quite stressful for a newly planted tree. Initial studies on this have found that it may take longer for these trees to become established, but in the long term, these trees tend to develop root systems that allow them to catch up to trees that did not undergo any intervention.
And then some species are just notorious for girdling roots in urban settings, like maple trees. Another reason to select a tree that is not a maple!
Good Growing Tip of the Week: Looking for arborist woodchips? Many tree care and utility companies are looking for places to dump their woodchips. It never hurts to give them a call and see if you can get a load. Many municipal yard waste sites also have free woodchips for their residents.