The term “locust” can apply to several different species of trees with legume-like seed pods. Two of the most common kinds in North America are the honey locust and black locust.
Honey Locust Trees
Among landscaping trees, honey locust has become very common, and with good reason. The honey locust (Gleditsia triacanthos) is a fast-growing tree. It grows as much as 20 feet in the first 10 years and can eventually grow 70 feet high. Unlike many fast-growing trees, though, the honey locust does not have invasive roots or weak wood. It is a long-lived tree that tolerates wind storms and ice. It also tolerates salt, foot traffic, pollution and compacted soils.
The tree has attractive gray-brown bark and an open, graceful canopy with tiny, oval leaves. Unlike large-leaved trees, the lacey leaves of honey locust allow sunlight to filter to the ground below so grass and plants can grow. The fruit of the honey locust is a pod, which has edible pulp on the inside.
In the fall, the leaves turn yellow. Because of their size, honey locust leaves are difficult to rake up, but they tend to dry up and blow away on their own eventually, although they can get tracked into the house if the tree is planted near an entryway.
Varieties and Types of Locust Trees
Native honey locust trees have long thorns and an awkward, upright growth pattern. These trees also produce brown seed pods. Look for hybridized honey locust trees that are thornless and podless.
‘Sunburst’ has yellow leaves that emerge in the spring and turn green as they mature.
‘Shademaster’ has dark green foliage and open, ascending branches.
In some areas, cankers and root collar rot are serious problems for honey locust trees. Cankers first appear as flattened or discolored surfaces on the branches and trunk of the tree. Over time, cankers can spread and completely girdle the tree, causing tree death. Cankers also cause slow growth, yellowing leaves or sparse leaves. Root collar rot is a similar disorder that appears at the base of the tree as a yellow or white area.
To prevent canker and root collar rot, keep trees vigorous and healthy. Water during dry periods, especially if the tree isn’t in an irrigated lawn. Be careful when mowing around the tree not to injure the trunk because injuries provide an entry point for these diseases. Prune out infected branches, cutting limbs at least 12 inches below the infected area. Disinfect pruning tools between cuts with a solution of 1 part bleach to 10 parts water.
Black Locust Trees
Black locust (Robinia pseudoacacia) is found throughout the United States in woodland areas and along stream banks. Like the honey locust, the black locust is a fast-growing, tough tree that tolerates drought, salt, pollution and poor soil. It grows best in full sun with moderate moisture.
Black locust trees grow 70 feet tall, although most trees range between 30 and 50 feet tall. The trees have small, blue-green leaves with a compound, alternate form like honey locust trees. In the spring, the tree is covered with showy, fragrant blossoms that attract millions of bees. Unlike honey locust trees, the seed pods of the black locust are not edible. In the fall, leaves turn dull yellow before dropping.
Black locust trees are known for their strong wood. Pioneers were said to have used the wood to make nails for building ships. Black locust wood makes a long burning firewood, as well, although the wood is difficult to cut. The wood is rot-resistant and makes excellent fence posts or raised beds.
The trees are used infrequently as landscape trees for a few reasons. First, although the wood is strong, branches are brittle and prone to breakage in high winds. The trees also have thorns. Black locust trees are very susceptible to attacks by the locust borer, which often prove fatal. The trees are more often used to control soil erosion or as a timber tree.
Growing Locust Trees
Plant locust trees in full sun, spaced at least 30 feet from other trees. Water trees frequently the first year as the roots become established. Older trees rarely need additional irrigation or fertilizing, especially if they are in an irrigated, fertilized lawn.
How to Plant and Take Care of Your Honey Locust Tree from Utah State University Extension
Black Locust: A Multi-Purpose Tree Species for Temperate Climates from Purdue University
This YouTube video teaches more about the black locust tree.
When she’s not writing about gardening, food and canning, Julie Christensen enjoys spending time in her gardens, which include perennials, vegetables and fruit trees. She’s written hundreds of gardening articles for the Gardening Channel, Garden Guides and San Francisco Gate, as well as several e-books.