A: That is a tough question. Most people go by the size of the plant in order to determine into which category it will best fit. However, we know the environment can play a key role in deciding the mature height of a plant. Some of the environmental factors are sunlight, available water, soil conditions, soil pH and availability of soil nutrients. In addition, one cannot ignore genetics. A tree or shrub has only a certain potential to reach a maximum height even when environmental conditions are ideal.
So, how can we determine whether a plant is a tree or shrub? I am certain we could easily get several definitions that would be satisfactory but I am going to use Cornell University’s definition:
“Trees are woody, perennial plants that have one central stem, are generally more than 12 feet in height, and normally have a distinct head. Shrubs are woody, perennial plants that have a number of stems usually produced from near the soil line of the plant. Shrubs are generally less than 12 feet in height but some exceptions can reach 20 feet or more.”
It is not a perfect definition, but it is a starting point.