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Is Your Tree Over the Hill?

While the age of a tree has no bearing on the care it needs, knowing its age can satisfy many a curious mind.

When the Garden Geek makes the occasional house call, it’s not uncommon for homeowners to ask him how to know the age of their trees. Of course, his customary answer is that the tree’s age has no bearing on how to care for it.

Still, I’d be curious to know the age of my trees. Curious minds and all. Fear not, fellow gardeners. I leaned on him a bit and he finally divulged the details to determine the age of your trees. You’re welcome.

Step 1. Using a diameter tape measure the diameter at breast height of your tree. If you don’t have a diameter tape, use a cloth measuring tape and divide the number by 3.1415 (pi).

Step 2. Find the mean annual increment growth (in inches) of your tree. You can do this by taking a professionally done core sample and measuring the rings, or you can assume it’s about ¼ inch to 1/6 inch per year.

Step 3. Follow this equation: Diameter of tree (DBH) ÷ mean annual increment growth = age of tree. It’s best to retain the fraction form. For example, a 30-inch live oak is between 120 and 180 years old (30 divided by ¼ = 120).

That’s it! You may not know the day your tree was born, but you could celebrate it annually by gifting your precious tree with a layer of compost or mulch.

Happy tree aging!

Sarah Gorton
Sarah Gorton
Sarah Gorton is a Planner with the SAWS Conservation department. She is passionate about bats and native plants, with a particular fondness for horseherb! Sarah has completed certifications through Texas Master Naturalist and Native Plant Society. When she isn't working on her research on the use of native grasses for uptaking pollutants at UTSA, she can be found making stained glass or hanging out with her two Chihuahuas.
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