Old ash tree dying slowly, what are the possibilities?

We have a more than 20-year-old ash tree that has been slowly dying back for about six years. Originally, the tree was very plush and about 20 feet tall.

Beginning about five years ago, the inner and lower branches began to die, with leaves first yellowing and then falling off. I thought it was stress from watering combined with an aphid infestation that year, but we have not had insect problems since that time and I see no evidence of ash tree borer anywhere on the trunk.

My watering for the lawn area around the tree has not changed in the 12 years we’ve been here other than watering a bit longer at very hot times of the year.

I would like to save the tree if at all possible. Any suggestions?

— Shawn

I’ve come up with three possibilities.

The first one is a watering problem, but it doesn’t sound as if this applies in your case.

The second possibility is borer. I know you didn’t find any evidence of them, but their signs are pretty subtle and easy to miss. Lilac ash borer seems to be more prevalent on ash trees the past several years and is far and away the most common reason for branches dying off one by one.

Typically, if you lose a branch that’s larger than one and one half inches in diameter, you should see evidence of their galleries when you strip some of the bark off of the dead branch, though occasionally that damage is a bit below where you think the dead branch ends.

The last explanation pertains to the possibility of the tree being planted too deeply.

Normally, I expect to see a prominent “root flare” at the base of the trunk above ground level which would indicate proper planting depth. Though there’s a slight widening at the trunk where it enters the ground in the photo you sent, it’s not as pronounced as I would expect.

There are two potential ways that problems will manifest themselves when a tree is planted too deeply. One is quick, the other slow.

The quick one is oxygen starvation to the roots resulting in stress, dieback and even death in the tree soon after it’s planted. Obviously, since your tree is past that age, this isn’t what’s going on for you.

However, there can be problems that don’t manifest themselves until years after the tree is planted. One of these is that a tree can develop a fungal infection at the base of the plant called a collar rot. The buried trunk tissue isn’t equipped physiologically to cope with being buried and damp all the time which can lead to the problems you’re seeing. 

Another possibility is that your tree has developed what’s called a girdling root. A girdling root is when a root circles or partially circles the base of a tree at or just below the soil surface, slowly choking off the flow of water and nutrients between the roots and the top of the tree.

The root also can compress and weaken the trunk of the tree at the base, which causes the tree to lose its stability. The result of a girdling root is the tree shows a slow decline in health and often suffers a premature death.

Even though it appears your tree is set too deeply, plants are adaptable and resilient.

Carefully excavate the soil away from the base. This is difficult to do without injuring the base of the tree. It’s best done with a small shovel or a hand trowel, just taking your time, and then using a jet of water from the hose to further expose the tree collar structure. 

If you find a girdling root, it should be cut and removed if it isn’t imbedded into the trunk. If it’s imbedded, you still want to cut the root but do not remove it. Leave it in place and rebury everything.

The tree may recover or it may not. You’ll have to wait some months or even years to see.

Dennis Hill is the nursery manager at Bookcliff Gardens, bookcliffgardens.com. Send questions to Bookcliff Gardens, 755 26 Road, Grand Junction 81506; or email .(JavaScript must be enabled to view this email address).


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