Why do my trees and shrubs always get bigger than they are supposed to? What does Mature Size mean?
After careful planning and selection it never fails, your shrub or tree gets substantially taller and wider than it was supposed to. Diligent pruning is then necessary to keep the plant from overgrowing the space you allowed, and eventually you wind up digging it out because it grew way too large way too fast. Why does this always happen? It is not because we are extraordinary gardeners, as much as we would all like to believe that.
Just what does the term “mature size” mean that we see in plant descriptions? It depends on who you ask. A forester, an arborist, the power company, a nurseryman, a botanist, a landscaper, all have a different definition of mature size. Some of the definitions by these professionals are:
- A tree that has reached a desired size or age for its intended use.
- Complete in natural development or growth.
- A tree that has a well-developed canopy.
- Fully developed in the middle half of its usual life expectancy and is still retaining good vigor.
- Full height but still spreading its crown.
- Size at ten years growth.
There are serious conflicts with these “definitions”. When you consider that some trees and evergreens live to be well over 100 years old, it may reach completed development and bear fruit or seed in 10 years or less but will continue to grow taller and wider for many many years. A well developed canopy can occur in less than ten years depending on the growth rate. The middle of life expectancy could be 50 years or more and the plant will continue growth at a slow rate. Full height at 100 years will certainly be substantially larger than ten years growth.
Plant descriptions in books, catalogs and nursery listings state a mature size in height and width. Nearly always that size is at ten years growth. But they don’t tell you that, and they don’t tell you how many more years the plant will live and at what rate you can expect it to grow. I know from experience that the complete information is sometimes impossible to find for any given plant. If you have looked at the tree and evergreen descriptions on this site you will find as much information as is available for the plant. Wherever possible the information is given as fully matured size at the life expectancy of the plant. But often it is necessary to indicate potential size at 10 or 20 years time and perhaps then indicate how many total years you might expect it to live. Whatever is available to help you determine ultimate size will be listed.
There have been attempts to standardize information, but there has been little agreement about how to clarify information, so it seems to only add to the confusion. Much of the trade (nurseries, landscapers, etc.) have adopted a very general guide related to tree size that generally seems to also apply to large evergreen trees:
Small Tree: 12 - 30 feet tall
Medium Tree: 30 - 50 feet tall
Large Tree: over 50 feet tall. (keep in mind that some of the tallest trees are over 200 feet)
Deciduous, and sometimes evergreen shrubs are often categorized as follows:
Low growing: under 5 feet tall
Intermediate: 5 - 8 feet tall
Large: over 8 feet tall
Of course all this information will only help you just so much, it is still somewhat vague and of course site and soil conditions can vary growth rates quite a bit. Any specific information regarding growth rates and ultimate size that is available for specific plants will continue to be added to the plant listings on this website if it is available. Be patient - this is a long work in process!
top of page previous article next article