When it comes to worrying about their trees’ trunks and bark, most folks have those topics ranked in the five-digit numbers – down below sharpening their drill bits and checking the expiration date on the salt.
Let’s put these in human terms, however. Trunks are the skeletal support systems of our big shade trees, and bark is their skin. We value our skeletons, and we know that skin is the biggest and one of the most critical organs of the human body. Same things go for our trees. Let’s take off from there.
When you plant a new shade tree you want to be certain it’s plumb with its world. You get that one chance to get it straight with its surroundings. Set it in its new planting hole vertically. Stake and guy it to hold it taut and erect. Most veteran tree people suggest using three stakes positioned 120 degrees apart, one due south (direction of prevailing winds in the summer), one northeast and one northwest.
Keep the cables or wires taut for the first couple of years until the tree’s roots are firmly anchored into the surrounding soil. You’ll know that has happened when the tree has put on several inches of active new growth. Until it does, leave it staked.
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Cable and wire can do serious damage to tree trunks. You see it all the time, and it’s a crying shame. Crews do a great job of staking and guying new trees, but those crews move on and no one remembers to remove the cables two or three years down the road. The branches start to grow and develop and before long they have encircled the cables to the point that they start to bind.
We halt the action long enough to explain the anatomy of a tree trunk’s interior. The outer cylinder is the bark, functioning primarily for protection. The next layer in is the phloem. That cylinder conducts manufactured sugars from the leaves down to the roots. Inside the phloem is the cambium (function to be described in a moment) and inside the cambium, making up the bulk of the “wood” of a tree’s trunk is the xylem, through which raw materials water and nutrients are carried from the roots up to the leaves to be involved in photosynthesis. The cambium is the tissue that gives rise to more phloem to its outside and more xylem to its inside.
Now back to our movie. The cable is beginning to bind its way into the trunk as the trunk grows around it. First the bark is severed, then the phloem. Eventually it begins to take a toll on the cambium. Somewhere in there the supply line of sugars down to the roots is cut and the plant begins to weaken, then die.
So that’s one way that we can ruin a perfectly healthy new tree – by failing to remove the wires that were holding it upright.
By the same token, if we buy a balled-and-burlapped tree that has nylon twine tied around its trunk, that twine can do the same thing a year or two later. Nylon doesn’t decay. On a personal note, I lost three dogwood trees that had tiny grower tags around the bases of their trunks. I never saw the tags when I planted them, but eventually, when the trees started declining, I found them girdling the trunks right at ground line.
If we use line trimmers carelessly we will do the same kind of harm to our shade trees. We’ll cut through the bark, sever the phloem and cut off those supply lines. You ought to have a trunk guard you carry around with you when you’re trimming the grass near your trees. Clip it in place while you’re working to prevent this kind of damage. The option I choose, however, is simply to “feather” the grass down to bare ground 2-3 inches out from the trunk all the way around. I never get near the bark with my trimmer line.
New trees have very thin bark. That’s especially true for Chinese pistachios and oaks, notably Shumard red oaks and chinquapin oaks. The trees have been grown close to one another in the nursery, but when we take them home and plant them they’re out in the open. Suddenly their trunks no longer shade one another, so sunscald and subsequent borer invasion become big issues. I use the phrase “non-negotiable” to stress the importance of protecting the trunks of these new trees for their first couple of years with paper tree wrap. Apply the wrap in spirals from the ground up to the lowest branches. It will hold itself in place, and it will literally save these trees. Once you have a trunk with splitting bark and borers it’s probably too late to try this.
To this point we’ve focused primarily on negatives and how to avoid them. Let’s spend a moment paying homage to the beauty bark brings to our landscapes. From the coarse-textured trunks of bur oaks and cottonwoods to white bark of crape myrtles and sycamores, bark is a fascinating fine point of horticulture. At no time is it any more noticeable than in the middle of winter. Look around and revel in it right now. Bark will open up a whole new appreciation of nature.