Question of the Week – Number 2: August 22, 2019

“Why is the bark on my tree splitting?”

Before I get into an answer we need to discuss two basic facts. First, bark is a dead tissue. As such, it cannot expand. Hang onto that information. We’ll come back to it later.

And, remember that bark serves to protect trees’ trunks from outside injuries. Most of those are obvious, like mower wheels and line trimmers. Bark does what it can to protect trees from being gouged. But there’s more to that story, too.

It’s absolutely normal for a crape myrtle to shed its bark. They have what is known as “exfoliating” bark.

For some trees, sloughing bark is absolutely normal…
Bark cells are dead. Remember that? Sloughing of bark is a routine process for almost all trees. Bark cells grow to full size, then they die. As the tree’s trunk grows thicker (like a waistline), all it can do is pop off.

For some trees, like cedar elms and magnolias, that sloughing involves small chunks of bark that are hardly noticeable. However, for others like paperbark maple, river birch, sycamore, crape myrtles, and sometimes even pecans, those sheets are quite long and very conspicuous. But that sloughing is absolutely not threatening.

And then there are times when splitting, peeling bark is a big concern…
It’s when oaks, maples and Chinese pistachios, among other trees, start losing big pieces of bark that you begin to worry about sunscald, decay and borers.

These are all trees that have very thin bark when they’re young. While they’re growing next to one another in the nursery they offer protection of mutual shading so nothing much happens.

Red oaks and other types of oaks are very commonly hurt by sunscald. I say that wrapping their trunks following planting is “non-negotiable” to avoid problems like this that will cost you the trees within just a couple of years.
Red maple was planted into a new commercial landscape in McKinney without any protection from western sun. Its bark is splitting badly. In fact, of the dozen maples they planted, two are dead and the other 10 soon will be. All could have been saved with use of paper tree wrap at planting.
Extreme damage done by exposure to west sun is obvious on this closer view of red maple trunk that was left unprotected for first 18 months after planting. This tree will be lost. Nothing can be done at this point.

When we set these trees out into our landscapes exposed to the hot Texas sun they soon run into problems. The west and south sun in the summer beats on their exposed trunks, overheats the wood and ultimately causes it to crack and peel away after three or four years.

Continued Below

Without that bark the conducting tissues that carry sugars from the leaves down to the roots are severed and the tree ends up dying.

This is why I say that wrapping trunks of new oaks, maples and Chinese pistachios is critical for their first couple of years. Paper tree wrap is sold by nurseries and hardware stores. Several types are available, and for just a few dollars per tree they can make a life-saving difference.

Hypoxylon canker causes post oaks to lose bark…
Following the extreme drought of 2011 many of our tree species were severely damaged. Post oaks were especially hard hit, and within a couple of years (and even up to today), large pieces of bark were falling off.

There is an opportunistic organism known as Hypoxylon canker. In its own right it rarely attacks healthy trees. But when a tree is weakened it can move in. Having seen many cases of it, the folks at Arborilogical Services in DFW keep this on their website.

Note: In the spirit of openness, Arborilogical Services advertises in e-gardens and on my radio programs and website. They do all of the maintenance work on the trees in the Sperry landscape as well.

Posted by Neil Sperry
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