Honey Locust (Gleditsia triacanthos)

Honey Locust, Thorny Locust, Thorny Honeylocust

The thorns on a native Honey Locust make the thorns on a rose bush look like peach fuzz. But thankfully, while every rose has its thorns, this is not so with Honey Locusts. Most Honey Locusts that you will find have been cultivated to have no thorns whatsoever. As with the previous trees that have been examined including the Norway Maple and White Ash, the Honey locust is a very common tree. It too is frequently planted along boulevards and in backyards.

I. Appearance and Characteristics 

The Gleditsia triacanthos (Honey Locust), also known as the thorny locust or thorny honey locust, is a deciduous tree in the family Fabaceae, native to central North America where it is mostly found in the moist soil of river valleys. Honey locust trees are highly adaptable to different environments, and the species has been introduced worldwide. Outside its natural range it can be an aggressive, damaging invasive species.

The honey locust, Gleditsia triacanthos, can reach a height of 20–30 m (65–100 ft). They exhibit fast growth, but live a medium life span of about 120 years. The leaves are pinnately compound on older trees but bipinnately compound on vigorous young trees. The leaflets are 1.5–2.5 cm (1⁄2–1 in) (smaller on bipinnate leaves) and bright green. They turn yellow in the autumn. Honey locusts leaf out relatively late in spring, but generally slightly earlier than the black locust (Robinia pseudoacacia). The strongly scented, cream-colored flowers appear in late spring, in clusters emerging from the base of the leaf axils. The trees are polygamodioecious: most are strictly dioecious with male and female flowers on separate trees though some have bisexual flowers with a few male or female flowers on the same tree.

The fruit of the honey locust is a flat legume (pod) that matures in early autumn. The pods are generally between 15–20 cm (6–8 in). The seeds are dispersed by grazing herbivores such as cattle and horses, which eat the pod pulp and excrete the seeds in droppings; the animal’s digestive system assists in breaking down the hard seed coat, making germination easier. In addition, the seeds are released in the host’s manure, providing fertilizer for them. Honey locust seed pods ripen in late spring and germinate rapidly when temperatures are warm enough.

Honey locusts commonly have thorns 3–10 cm (1–4 in) long growing out of the branches, some reaching lengths over 20 cm (8 in); these may be single, or branched into several points, and commonly form dense clusters. The thorns are fairly soft and green when young, harden and turn red as they age, then fade to ash grey and turn brittle when mature. These thorns are thought to have evolved to protect the trees from browsing Pleistocene megafauna, which may also have been involved in seed dispersal, but the size and spacing of them is less useful in defending against smaller extant herbivores such as deer. Thornless forms (Gleditsia triacanthos var. inermis) are occasionally found growing wild and are available as nursery plants. Hybridization of honey locust with water locust (G. aquatica) has been reported.

The species is a major invasive environmental and economic weed in agricultural regions of Australia. The plant forms thickets and destroys the pasture required for livestock to survive. The thickets choke waterways and prevent both domestic and native animals from drinking and also harbor vermin. The spines cause damage to both people and domestic and native wildlife and puncture vehicle tires. In much of the Midwest of the United States the honey locust is also considered a weed tree and a pest that establishes itself in farm fields. In other regions of the world, ranchers and farmers who employ monocropping deem honey locust a nuisance weed; its fast growth allows it to out-compete grasses and other crops.

II. How to Grow and Care

Sunlight

The tree should be planted in a location where it gets full sun (at least six hours of direct sunlight on most days).

Temperature and Humidity

The honey locust is able to grow in a variety of climate conditions, but it will perish if exposed to temperatures below minus 33 degrees Fahrenheit.

Watering

When getting established during its first year, a young Honey locust should be watered regularly. Ensure soil doesn’t dry out (while also being sure not to oversaturate it) by providing weekly waterings 鈥?slow or drip-style irrigation is particularly effective. As they mature, these trees become much more drought tolerant and should only require supplemental waterings during long periods of very hot or very dry weather.

Soil

Honey locust can grow well in different types of soil. Loam is ideal, but the trees are also quite tolerant of sand or clay. This tree is also tolerant of salty soils.

Fertilizing

Honey locust respond well to annual feedings, especially when young and growing rapidly. Usually, a simple, balanced, slow-release fertilizer formula is your best bet. There are two good times to feed: in late fall, or in early spring. Either way, make sure not to damage your tree by applying fertilizer directly to its trunk or exposed roots.

Planting Instructions

Honey locusts are sold in the tree nurseries as bales. It is advisable to plant them in spring or fall as mild temperatures and rainfall will encourage a good start. It is important that you insert a sturdy support post into the generously dimensioned planting hole before you plant the tree. Before insertion, the knot must be loosened from the cloth or cut open. Then you fill the excavated earth into the planting hole, compact the earth by stamping on it and fasten the support post to the trunk with a rope. The newly planted sapling must be watered thoroughly, otherwise the tiny honey locust will not grow well.

Pruning

Mature honey locust trees need little pruning except to remove dead or diseased branches, but until they are mature, you should prune them every five years or so to shape them as desired. This typically means keeping the canopy relatively open and airy. Branches that cross and rub can be susceptible to developing canker, which can spread and kill a tree. The best time to prune is in late spring to fall when sap flow has lessened somewhat.

Propagation

The cultivar ‘Sunburst’ is a registered trademark that cannot be propagated.

Pests and Diseases

Honey locusts are somewhat susceptible to a variety of insect pests, including mites and webworms. Pests are less likely to be serious problems if you keep the tree in good condition with adequate watering and by regularly removing dead and damaged branches. The tree can also be attacked by diseases such as cankers and root collar rot.

Winter protection

Heavy frosts can damage the Honey locusts. This is especially true for young trees. This can be remedied by a wire frame that is placed around the trunk and filled with leaves. With older trees it is sufficient to cover the ground with a thick layer of bark mulch.

III. Uses and Benefits 

  • Ornamental uses

Gleditsia triacanthos has made a name for itself as a city tree in Europe with its beautiful, light crown and its robust attitude towards exhaust fumes, road salt, frost, heat and hail. You can find honey locusts in many places on streets and in green spaces. However, landscape planners rely on varieties such as ‘Inermis’ or ‘Skyline’, which are similar to the species, but whose trunk and branches do not have thorns. The pale green foliage, resembling ferns, makes honey locusts look delicate despite its size. Varieties that remain smaller than the species and are thornless are suitable for gardens. With good exposure to light and the deeply growing roots, they can be planted as a ground cover.

  • Culinary uses

The pulp on the inside of the pods is edible (unlike the black locust, which is toxic) and consumed by wildlife and livestock.

Despite its name, the honey locust is not a significant honey plant. The name derives from the sweet taste of the legume pulp, which was used for food and traditional medicine by Native American people, and can also be used to make tea. The long pods, which eventually dry and ripen to brown or maroon, are surrounded in a tough, leathery skin that adheres strongly to the pulp within. The pulp—bright green in unripe pods—is strongly sweet, crisp and succulent in ripe pods. Dark brown tannin-rich beans are found in slots within the pulp. Likewise, its edible seed has nutritional potential, and the flour made from its cotyledons constitutes a food source with various potential uses for pastry and bakery, among other gastronomic uses.

  • Other uses

Honey locusts produce a high quality, durable wood that polishes well, but the tree does not grow in sufficient numbers to support a bulk industry. However, a niche market exists for honey locust furniture. It is also used for posts and rails because of the dense, rot-resistant nature of the wood. In the past, the hard thorns of the younger trees were used as nails and the wood itself was used to fashion treenails for shipbuilding.

Honey Locust (Gleditsia triacanthos) Details

Common name Honey Locust, Thorny Locust, Thorny Honeylocust
Botanical name Gleditsia triacanthos
Plant type Native Plant
Hardiness zone 3a, 3b, 4a, 4b, 5a, 5b, 6a, 6b, 7a, 7b, 8b
Growth rate Fast
Harvest time Fall
Height 60 ft. 0 in. - 80 ft. 0 in.
Width 60 ft. 0 in. - 80 ft. 0 in.
Sunlight Full sun (6 or more hours of direct sunlight a day)
Soil condition Clay
Flower color Gold/Yellow
Leaf color Green