Specific epithet: triacanthos
Variety: inermis (Fruit pods and thorns absent)
Common name: Honey-Locust
Erect or spreading with a low canopy and deciduous foliage.(1)
Longevity 50-150 years. Shorter lived in urban areas and stress.
Honey locusts are polygamo-dioecious trees, meaning male and female flowers are on separate trees, but all trees also have perfect flowers.(3) Male sex organs are catkins which are pendulous cylindrical flower clusters. Female flowers are fragrant but not showy and often lost in the expanding foliage. Perfect flowers have both male and female sex organs so they can self pollinate and produce fruit. This cultivar however is fruitless, but other cultivars have 6-8" long red-brown leathery pods that become dry and twisted. A flower cluster can be seen below. Honey locusts can be propagated by seed, but this does not always guarantee the seedling will have all the same features as the parent, meaning color and having absent thorns. Thornless cultivars are usually propagated by budding or grafting the desired traited tree onto a rootstock of another tree. This is essentially cloning the desired tree onto a different set of roots to get a new tree.(5)
Honey locusts are native to North America and can be found throughout the United States and south-eastern parts of Canada.(1) It has been grown in urban areas where air pollution and compacted soil is common, and can also tolerate salt stress.(2) Honey locusts are hardy adaptable trees, which can do well in most climates. They are tolerant of lawn watering as well as drought. They can survive in acidic to alkaline soils, but will do best in neutral soils. They can also survive some shading, but do best in full sun. The Sunburst cultivar is hardy through zones 3-7.
Wood Descrition and Uses
The heartwood is medium to light reddish brown in color, while sapwood is light yellow.(4) The grain is usually straight or slightly irregular. Endgrain is ring porous with large earlywood and medium to small latewood pores. Tyloses absent, growth rings are obvious, and rays are visible without a lens.(4) Moderately rot resistant but suseptible to insect attack. Common uses are furniture, fence posts, utility lumber, or turned objects.
There are no special needs for planting Honey Locusts, and general tree planting rules should be applied. It should be planted in the spring of fall, for summer planting may be too hot and stressful. A hole should be dug wider than the root system to allow roots to grow horizontally, but not much deeper otherwise the tree may sink while settling. It is important that the roots stay near the surface with only an inch or so of soil above them. If planted too deep the roots may grow up to obtain more air and eventually expand as they grow and cut off water flow upward to the tree, resulting in poor health and possibly the death of the tree. If planted too near the surface however aged roots may become an issue with lawn mowers. When back filling with soil air gaps should be filled so there is soil contact with the roots so rot does not occur. Newly planted trees should be watered carefully so they do not become stressed, but they should not be over watered to the point where the tree does not get air exchange in the roots. Where lack of water may result in wilting, as can flooding or over watering.
Honey Locusts have a natural airy growth habit, so pruning is normally not needed. Dead branches should be removed, as should co-dominant trunks if they occur. If branches are low to the ground and in a walkway they may also be pruned away. It is best to prune out branches while they are young to avoid large wounds. When pruning larger heavier branches be sure to cut so the bark does not peel and result in a larger wound with the three cut pruning method, as shown to the below. Pruning should also be done outside the branch collar to avoid damaging trunk tissue. It is best to prune in late winter or early spring, as this is the time of fast growth in the tree and it can more quickly recover from wounding.
What can you do with a Honey Locust?
Honey Locusts are popular trees because they grow fast, have relatively strong branches, are aesthetically pleasing, and are tough trees tolerant of many environments.
These do well planted in yards, parks, and along streets. They are nice planted near homes because of their compound leaves. In the summer the leaves fill out and provide shade for the home, lowering cooling costs, but in the winter have very open canopies allowing sun exposure to the home reducing heating costs. For this reason Honey Locusts are good energy efficient trees. Even planted 1,500 feet away they have been shown to reduce energy costs, but a good distance from the home would be around 30 feet. Because of the compound leaves they also allow some sun through the canopy to allow grass to grow up to the trunk.(5)
Because of their adaptive ability to withstand compact soils, a range of soil pH, heat, flooding and salt, these are popular choices along sidewalks as well as in yards. Honey locusts, especially the Sunburst cultivar, provide beautiful foliage colors. The leaves start out yellow, turn green in the summer, and then turn golden yellow again in the fall.(3) The sweet smelling flowers are attractive to bee pollinators, and cultivars with the fruit pods attract wildlife which eat them such as deer, squirrels, and rabbits.(5) This is because of the honey like taste of the pods where it derives it name. The pods may also be fed to cattle and goats. Some Native Americans even dried the pods, ground the pulp, and used it as sweetener and thickeners. Fermented pulp was also used as energy alcohols, and the beans have also been cooked and used as a substitute for coffee.(1)
Disease and pests
The major disease of this tree is cankers which girdle and lead to the death of the tree. Canker symptoms include branch die back, reduced foliage, premature coloration and premature leaf drop. Cankers are found at the tree base, wounds, and at branch crotches. They appear as slightly flattened or sunken surfaces with callus ridges at the canker margin.(7) Infected bark will be loose with the wood beneath being dark red or yellow instead of the natural white color. These can be controlled by preventing wounds and promoting good healthy and vigor.
One of the most common Pests of Honey Locust are the Honey Locust plant bugs which pierce leaves and suck the sap. These mostly cause cosmetic damage to the tree, but when in high numbers can impact the health of young recently planted trees. If they are a concern an insecticide can be applied at bud break of the tree for this is when the overwintering eggs hatch, and they only go through one life cycle a season.