How to Determine the Age of a Tree

How old is the giant tree in your backyard? If you don't know the date the tree was planted, there are two main ways you can figure out how old it is. You can either cut it down or use an increment borer to count the tree's rings, or multiply the tree's diameter and the growth factor to estimate the age. See Step 1 to learn more about how to determine the age of a tree.

EditSteps

EditDetermining the Age of a Live Tree

Try to find out when it was planted. This is the only way to know for certain how old a tree is, since all of the other methods are simply estimates. If possible, conduct research to find out when the tree might have been planted. Ask older residents of the neighborhood or look at old photographs to try to date the tree.

Count the tree's whorls. Some species of trees, such as particular conifers, produce annual branch whorls. Counting branch whorls can be used to estimate the tree's age. This method is not as accurate as cutting down the tree and counting the rings, but it's a way to estimate the tree's age without having to kill it.^[1]
- Count the number of branch whorls above chest height.
- Add 1 to your total to account for the tip of the tree.

Multiply the diameter by the growth factor.^[2] A tree's growth factor is the measurement of the width it gains annually. If you know the average annual width of tree ring for that species, you can multiply it by the diameter of the trunk to estimate the tree's age. Different species' growth factors are dependent on their environment - for example, forest trees grow faster than city trees - so this method for determining a tree's age is truly an estimate.
- Measure the circumference of the trunk in inches. Use the trunk width at 4.5 feet off the ground.
- Calculate the diameter (circumference divided by pi).
- Multiple the diameter and the tree species' average growth factor. This will give you the approximate age of the tree in years. You can figure out a tree's growth factor by searching online or measuring the rings of a dead tree from the same species.^[3]

EditDetermining the Age of a Dead Tree

Fell the tree and count its rings. If the tree is already dead, you can count the rings on the exposed stump. The number of rings indicates the number of years the tree lived.
- Keep in mind that most trees produce a two-colored ring per year, a light spring portion and a dark summer portion.

Use an increment borer. This will take a small sample from the tree bark to the pith (tree centre). It's a way to count the tree's rings without cutting down the tree. The length of the borer should be at least 75% of the tree's diameter.
- Position the borer at average chest height (1.3 m) from the ground.
- Drill a sample.
- Confirm that your sample contains pith. If not, you will need to re-drill.^[4]
- Count the number of rings.

EditWarnings

Trees do not always produce one ring a year. Weather conditions, soil conditions, and other factors may lead to multiple rings, or no rings, being produced in a specific year.