Why Trees are Measured in Gallons

When shopping for trees you may ask yourself, why are nursery trees measured in gallons? Simply put, the size in "gallons" of a tree is a reference to the size of the pot its growing in; however, not every container of the same "gallon" size is made equal! In fact, most containers will not exactly equal the size quoted on them. To learn why, read on!

The practice of quoting tree sizes in gallons developed to streamline the trade of nursery trees as the American horticultural industry boomed following World War II. To make this trade more predictable, a standard was developed to the specifications of the American National Standards Institute. Today, this has resulted in a lengthy document outlining exactly what can be called a "__ gallon container", along with a number of other methods of measuring trees. If you're interested in seeing this document, the 2025 version can be found here.

Page 2 of the document specifies the required size ranges for containers. Taking a "#10" or "10 gallon" container as an example, you will find that the allowable range for this container is between 9-11.5 gallons. To ensure nurseries are not abusing the practice of quoting tree sizes based on their container rather than the tree itself, a brief note is provided on page 13 to define the extent of a root system that qualifies a tree for its container. This guideline also ensures the health of the tree as a tree planted in a pot which is too large will be prone to falling over, while a tree planted in a pot which is too small will become "root bound". This condition describes a tree whose roots have begun to encircle the container and become entangled, which can be detrimental to the tree's future success.

It's worth noting that in "Annex B" of the standards document, it specifically states that these standards are only intended to be used by professionals in the trade. These standards help to guide the terms of contracts which professionals use when dealing in wholesale quantities. The document explicitly states that for consumers of the retail trade (that's you!), these standards and techniques do not apply. In the case of retail consumers, only the standard consumer protection laws regarding deceptive advertising apply. 

Clear as mud? Yeah... Believe it or not, a lot of nurseries take advantage of this sizing scheme to "up-pot" trees. This is where a nursery will (for example) take a tree from a 10-gallon container and move it up to a 15-gallon container in order to sell the tree at a higher price. At The Tree Place, the only thing we take into consideration when moving a tree up in size is the health of that tree! It's not something we do too often, but trees do in fact grow! When shopping for a tree with us, if you're concerned about the size of the tree or quoted size of its container, feel free to ask. We're happy to provide you with any assistance we can provide. You're always welcome to call or text us at 817-561-9248.