Scientific Name
Gleditsia triacanthos
Honey locust is a tree native to the central United States between the Appalachian Mountains and the eastern edge of the Great Plains. This is a relatively fast-growing tree that can become large at maturity, typically reaching a height of 65 feet in the Colorado area. The current champion honey locust in Colorado is 88 feet tall and lives in Fort Collins. Honey locusts can begin flowering and fruiting as early as five years of age and can live over 100 years.
Honey locust leaves are compound or doubly compound, with the individual leaflets being in the range of a ½ to 1 ½ inches long. The twigs lack a terminal bud which gives rise to a jagged branching pattern visible in the dormant season. The branches develop stout, sharp, three-pointed spines that also grow from the trunk. These are likely a prehistoric defense against now-extinct browsing animals that once ate the tree's bark, leaves or twigs. For the most part, the spines are only produced on the lower 15 or so feet of the tree, which could reflect the reach of the tallest browsing animals in the past.
The flowering of honey locust trees is complex. Many trees produce only male or only female flowers, but others produce mostly flowers of one sex and a lesser quantity of flowers of the other sex. This trait has complicated the selection of seedless breeds, which naturally focused on propagating male trees, because some of the males continued to produce the classic fruit pods of the legume (large pea) family. Said pods are up to a foot long, flattened, often twisted or curved, and may contain as many as 20 small hard-coated seeds. The interior of the pods is filled with a sweet edible spongy pulp that surrounds the seeds, and this has given the tree its common name. As a honey locust tree gets older, its bark breaks apart into long, smooth strips that run up and down the trunk. These flat ridges are separated by deep, vertical cracks.
Honey locust is a very adaptable tree that does well in varying soil types and is well-suited to the climate in the Colorado area. In nature, it often grows in wet sites but is also able to tolerate drought and salty soil. Because its foliage is lacey, the tree doesn’t produce dense shade which allows grass and other plants to grow up to the trunk. The fineness of the foliage also means a relatively easy leaf cleanup in the fall. Like many plants in the legume family, this tree has a partnership with tiny symbiotic bacteria that live in its roots. These bacteria fix nitrogen from the air to help the tree grow, which allows it to prosper even in poor soil. Both this feature and the ability of its seeds to be spread by animals that consume the seedpod interiors (along with the seeds) has resulted in it becoming a problematic invasive plant in many countries where it’s been introduced. Equally, it’s considered a weedy tree in parts of the United States as well. Honey locust was planted in Denver to a limited degree beginning early on, and despite its positive attributes, the thorn and pod litter issues limited its use. Only after thornless and nearly pod-less breeds were marketed by the nursery trade after World War II did the tree catch on in landscaping in Denver (or anywhere else, for that matter). Since that time, honey locust breeds have become commonplace, if not actually overplanted. This tree on the Regis mini-quad is one of the original honey locusts, thorns and all.