You may think that the difference between a tree and shrub are obvious – trees mostly tower above your head and shrubs do not. But that’s not always the case.
Consider this: A dogwood tree (depending on the variety) typically grows to a height between 13-25 feet. Mountain Laurel shrubs (depending on the variety) can grow 20-40 feet. So height is not the defining characteristic between trees and shrubs. Also, the mature height of trees or shrubs can often depend on growing conditions (amount of sun, shade or water, disease, pests, stress, competition with other plants, etc.).
What’s the botanical definition of a tree or a shrub?
We should look up the botanical definitions of trees and shrubs to know the difference for sure. But the problem is, neither is clearly defined in the sciences. (You sometimes need a microscope to know the difference).
Though no scientific definition exists to separate trees and shrubs, a useful definition for a tree is a woody plant having one erect perennial stem (trunk) at least three inches in diameter at a point 4-1/2 feet above the ground, a definitely formed crown of foliage, and a mature height of at least 13 feet.
Utah State University Forestry Extension
So the rule of thumb is that if a plant is perennial (comes back every season), woody, has a single stem, and grows to a height of at least 4-1/2 feet, it’s a tree. A tree also typically has branches above the ground that are supported by the stem, aka, the trunk.
If the plant is perennial, woody, and has no main stem but multiple stems that stand upright or grow at ground level, it’s a shrub. But not always. Are we clear?
Want to learn more? See these resources on trees and shrubs:
- Wikipedia/Tree
- Wikipedia/Shrub
- Plant Classification from North Dakota State University
- https://forestry.usu.edu/tree-identification/what-is-a-tree
- Popular Science: What is the difference between a tree and a shrub?