Tree or Shrubbery?

I love learning and sharing information with people who have an interest in gardening, as I continue my journey at the beautiful Wellfield Botanic Gardens. This winter, I am focused on learning proper pruning practices for the wide array of woody plants in the Gardens. In that spirit, I want to share some useful beginner information about what a tree or a shrub is. 

I have stumbled upon a bit of a gray area in the process of learning about woody pruning. What IS a tree exactly? What IS a shrub? This seems like a really simple question to answer. Of course, a boxwood is a shrub, right? How could a maple be anything other than a tree? I always thought there was a strict definition of each, but it turns out to be much more subjective. For example, here at Wellfield, there are multiple river birch (Betula nigra). I do not know about you, but when I hear the word “birch”, I always picture a large tree. There are a few river birch specimens along the West Promenade at Wellfield, and they look like “a river birch” to my mind.

If you take a trip over to the Garden Restroom building, you will find something with river birch characteristics, but you will immediately notice something peculiar: it looks like a SHRUB, not a tree! That messed with my whole classification of trees and shrubs. Shrubs tend to have many stems and are much shorter, but this does not always hold true. Trees tend to be taller and usually do not have many stems. Many trees will have fewer branches coming out of the main stem(s) at the base as well.

My focus has been on landscaping/horticulture definitions and classifications of the terms. An ecological point of view can also help shape how woody species are seen. There are many layers in a forest, and the tallest three are relevant to this discussion. There are very tall and wide canopy trees: think of an Oak or a Hickory. Under the massive canopy trees is a layer of smaller, understory trees. Understory trees are more the size of crabapples and dogwoods. The smallest woody layer is the shrub layer. The shrubs exist underneath the understory trees.  Ecologically, the tree versus shrub discussion is a bit more black and white without human interaction with the plants. Exceptions exist in the ecological world, too. Sassafras is a common plant in this area, and most of the time will exist in the shrub layer and not get much larger. A fully mature sassafras can easily join the understory tree layer, or even the canopy, if it is able to get the required light and nutrients. As you can see, the terms “tree” and “shrub” are a bit arbitrary, and there is not a right or wrong term in many cases.  

Knowing the concept of a tree or a shrub comes in handy for taking care of the garden. It is hard to prune a plant if you do not know what shape it naturally grows. Generally, a tree will be pruned with less lower branching than a shrub. Pruning with the plant’s natural growth pattern helps keep it healthy with a natural aesthetic look. Understanding its natural growth means you are not wrestling with it, which translates to easier work. Good luck practicing in your garden!

Cody Hoff, Lead Horticulturist

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