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Friday Garden Goods: "Why are Trees Measured in Inches?"

 "Why are Trees Measured in Inches?"

In the horticulture industry, standard shade and ornamental trees are typically measured by their trunk size. Measuring trees in inches can be confusing to those not in the industry. A common question we hear is, "How tall is a 3" tree?" The answer is that it varies, depending on the quality, growing conditions, and the species of the tree. In this blog post, we will answer and explain how different trees are measured and sized.


B&B Shade Trees in our Harvard Nursery

Understanding The Terminology of Tree Sizing

Standard shade and ornamental trees are measured by their caliper, or the diameter, of the tree trunk. By "standard" we mean trees with one trunk, versus a clump form, or multi-stem, tree. Evergreens, which have difficult to reach trunk sizes, are measured by height. Shade and ornamental trees measured in inches are also balled and burlapped, compared to those grown in containers, which are sized by their container size.

Container Grown:

Sold by size of the container or "pot size"

 Balled & Burlap:

 Evergreen & Clump Form Trees are measured by height


 Standard (Single Stem) Shade & Ornamental Trees are measured by trunk diameter


Any shade or ornamental tree measured with a #15, #10 or similar number is an indication that tree has been grown in a container. If it is measured by inches, you can be assured the tree is being sold in a balled and burlapped root ball. Typically B&B trees, as they are called, range in size from 1" to 4 1/2".  Their measurement, or the caliper, is taken 6 inches from the base of the tree.



How Does Inch Measurement Correspond to Tree Size?

What is the difference in size between a 1" Autumn Blaze Maple and a 4" Autumn Blaze Maple? Basically a 1" tree is about 150 lbs and can be easily transported and planted by a strong person willing to do the work. A 4" and up tree is an entirely different ball game. Don't worry for now about the height, but think of the rootball. The size of the root ball depends on the diameter of the tree, not the height.  In layman's terms, a 4" and up tree is a monster!  Think 1200-1500 lbs, 3-4 STRONG people, a big truck and a huge hole. Anything larger than a 4 1/2" tree generally requires a tree spade and special transportation.

In a nursery, the grower will measure each tree prior to digging. The caliper of the tree will tell them how big the rootball needs to be to encapture the majority of the root system. A larger sized shade or ornamental tree should have a LARGE rootball. In general, the size of the rootball is a good indicator of the quality of the tree.

How does the height of the tree compare to the diameter of the trunk?

The height of a tree depends on many factors, including the species, pruning, area of the country, and growing conditions. Consider trees grown in the south. They have a longer growing season, thus, are young trees when they reach a sellable height. In northern Illinois, it takes years longer to grow the same species of tree to a comparable height. We refer to these as slow grown trees. These trees may be of similar height but the caliper of the slow grown, locally grown tree is usually larger as well as the root ball. Southern grown trees of questionable quality may have smaller rootballs to save costs on the freight of shipping them north.

Pruning also can make a difference. Certified nurserymen will prune the young trees as needed, to ensure a nice, full canopy. Sacrificing some height can help the tree grow into a better all around speciman. Faster growing trees will grow tall before devloping a wide trunk, slower growing trees will grow wider trunks before they grow tall.

The height and caliper of a tree also varies by species. Some trees simply grow taller and faster than others. An experienced horticulturist will be able to help explain the different rates of growth amongst species of ornamental and shade trees.

Questions? As always, feel free to call The Barn Nursery for assistance. We are happy to answer any questions you may have.




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