Locusts are part of the pea family, Fabaceae, and can take the form of both trees and shrubs. They are all native to regions across North America, where they have since been cultivated for multiple reasons, including for use as hedging or erosion control.
There are several different varieties of locust tree that are commonly cultivated for ornamental purposes, as locusts have many positive attributes, both aesthetically and from a practical point of view. Read on to find out about the most popular types of locust trees available and their care needs.
Black Locust - Robinia pseudoacacia
The black locust tree is one of the most popular types of locust trees, probably because it has so many uses and is so easy to grow. It grows very quickly, in a variety of conditions. It can tolerate drought and poor-quality soil and can be found growing natively in woodland and along the banks of rivers.
Black locust trees are native to North America, and some examples can be found growing to heights of over 80 feet, though they typically grow to somewhere between 40 and 60 feet, with a large canopy spreading 30 feet across. Their branches grow in a non-uniform pattern leaving gaps amongst them that make for an excellent light shade of plants growing below (Royal Horticultural Society).
To grow a black locust tree, all you will need is a large space that benefits from full sun. These trees grow easily, even becoming mildly invasive in some regions. To prevent this problem, you will need to keep on top of the suckers. Otherwise, black locust trees may soon dominate your space.
The tree should also have good drainage as it prefers not to sit in soggy soil. However, it can adapt to growing in moist soil, just try to ensure it isn’t waterlogged. The tree is very tolerant of many other conditions, which some trees find less than ideal. It will cope well with drought, poor soil quality, high salt levels, and air pollution. The black locust tree is actually said to be able to improve the quality of the soil it is growing in, removing nitrogen from the air and releasing it into the soil. The tree is hardy through USDA growing zones 4 to 8.
The black locust tree typically flowers heavily, and this is one of the things that makes the tree so popular as an ornamental tree. The flowers grow in clusters that dangle from the tree and can measure anywhere between 4 and 10 inches in length. They are highly fragrant and are usually white, though some cultivars of the black locust tree can produce flowers in shades of pink and purple.
The leaves of the tree are oval and typically a blue-green color, though this does vary between cultivars. The base of the leaves of the black locust tree has short and sharp thorns, unlike the honey locust tree, which has thorns all over it. These thorns are said to be so sharp that they were once used as nails in the building.
Black Locust Tree Uses
Black locust trees are a hardwood tree, and they make excellent high-quality timber that is durable and strong. The wood of this tree is commonly used in manufacturing fences. The fact that the tree grows so quickly is also an advantage because it means high-quality wood can be produced in a short space of time. This is one of the main reasons that black locust trees are cultivated.
The black locust tree flowers profusely, with large clusters of beautiful blooms. These flowers are attractive to bees and provide a good source of nectar. Therefore, black locust trees are planted in regions where honeybees are operating to help them with their honey production.
Because black locust trees are so hard, the wood can be quite challenging to cut. However, it makes a brilliant source of firewood because its high density means it takes a long time to burn. This makes it much more efficient firewood than many others.
Black Locust Tree Cultivars
Frisia Black Locust - Robinia pseudoacacia 'Frisia'
This variety of black locust trees is commonly cultivated for its ornamental quality. It produces vibrant yellow leaves that sometimes turn a shade of lime green, bringing stunning and unusual foliage colors to any garden. It is slightly smaller in stature than the black locust tree, growing to a height of 40 feet with a spread of 25 feet.
Purple Robe Black Locust - Robinia pseudoacacia 'Purple Robe'
This stunning variety of black locust trees is also highly ornamental with interesting aesthetics. When leaves are young, they are tinged with touches of purple, and as the foliage matures, it develops to a deep bronze color. The flowers of this tree contrast the foliage nicely, in rich shades of pink and purple.
Twisty Baby Black Locust - Robinia pseudoacacia 'Lace Lady'
This black locust can be grown as a shrub or a tree. In the ground, it will grow to a compact 20 feet in height with a similar-sized spread, or if grown in a pot, it will reach heights of around 5 feet. Its name comes from the way its limbs twist and contort, giving it a very unusual look. Pruning back the plant in winter each year will encourage more twisting. It features dark green leaves that offer a contrasting background to the fragrant white summer blooms.
Honey Locust - Gleditsia triacanthos
The honey locust tree is popular in landscaping due to its large size, which is achieved in a short space of time because the tree is fast-growing.
Reaching heights of 100 feet in the wild, this tree will typically grow to between 40 and 70 feet when cultivated. It has a wide spread that provides useful shade in park grounds. It also has small leaves that don’t require collecting when they drop in the fall. This is because they are too small to pick up, but also small enough that they won’t cause any blockages or problems for drains and sewage systems. This is particularly useful for municipalities as it means less clean up and less cost to keep an area looking tidy in the colder months. All of these attributes have led to the honey locust tree being widely cultivated for use in city landscaping.
Honey locust trees are native to eastern parts of the United States. They are not as tolerant of inhospitable growing conditions as the black locust tree and prefer rich, moist soil to thrive. They will grow in less than ideal conditions, but high soil pH, high salt levels, and a lack of moisture will make the tree more susceptible to pests and disease.
Planting a honey locust tree is easy as they don’t mind being disturbed; just ensure you have a large space in a full sun spot and a big, oversized hole for the root ball as these tend to be much bigger than you would expect for the size of the tree.
The honey locust tree has attractive leaves that start out bright green and develop into yellow in the fall. After the leaves wall off in the winter, the tree will grow new leaves in the spring, typically a few weeks earlier than the black locust tree.
This tree has thorns on both the base of the leaves and long their branches. Starting out green, the thorns develop into dark brown as they age and become hard and brittle. They are very sharp and can measure anywhere up to 4 inches in length. This attribute has led to the honey locust tree also being known as the thorny locust tree, although thornless varieties are available.
The flowers of the honey locust tree are petite and pale green. In male trees, the flowers form in dense clusters, while female flowers are more loosely arranged. They have a very strong scent.
Honey Locust Tree Uses
The seed pods of this tree contain a sweet pulp that is edible, unlike the pods of the black locust tree, which are toxic and should not be consumed. The pulp was used as traditional medicine and food by Native Americans and is still used to make tea and in the production of beer. The seed pods are also used as food for wildlife and livestock.
Honey locust trees, like black locust trees, produce wood that is strong, durable, and high-quality. The tree has not been widely cultivated for the wood, but it is popular in niche markets for use in furniture.
The honey locust tree is most commonly used in city landscaping, as it has so many benefits. Unfortunately, over-cultivation has led to an increase in pests and diseases that affect the tree. In some areas, the tree has also become invasive to the point of being considered a weed. In farmland, it grows so quick that crops and grasses are poor competition against it. It also prevents animals from reaching natural waterways by creating barriers along rivers.
In spite of its name, the honey locust tree is not used to support the production of honey. The name is thought to be a reference to the sweet-tasting pulp contained in the trees seed pods.
Honey Locust Cultivars
Imperial Honey Locust - Gleditsia triacanthos inermis ‘Impcole’
This honey locust variety has a delicate feathery looking foliage that resembles a fern, starting out green through spring and summer, then changing to yellow in the fall before dropping in winter. It produces yellow-green flowers and grows to an average height of 35 feet. It is heat and drought-resistant and enjoys full sun.
Skyline Honey Locust - Gleditsia triacanthos ‘Skycole’
This tree takes the shape of a pyramid and has elegant fern-like foliage, both of which give the tree a very refined look. This variety is thornless, and it also does not bear fruit. This makes it a much easier tree to keep as the clean-up of the fruit from honey locust trees can be quite a messy job. Like many other locust trees, the skyline honey locust is adaptable to both moist and dry soil, and this variety, in particular, will grow happily in any soil pH. It typically grows to around 45 feet tall, with a spread of around 35 feet.
Shademaster Honey Locust - Gleditsia triacanthos var. Inermis ‘Shademaster’
This variety of honey locust grows even more quickly than most other locust trees, making it an exceptional grower. It is thornless and produces a very straight trunk. It can grow to between 50 and 70 feet tall with a spread of a similar measurement. The leaves of this tree are green, turning copper and yellow in fall. The shademaster also does not produce fruit, making it extra low maintenance. The yellow flowers bloom from this tree have a pleasant fragrance and are small and delicate (University of Florida Extension).
Bristly Locust - Robinia hispida
This locust is a shrub that is commonly known as ‘moss shrub.’ It grows to around 8 feet tall and produces attractive bright green leaves and showy pink flowers with an intense fragrance. The bristly locust needs to be grown in well-draining soils to thrive and has a low tolerance of poor growing conditions. In spite of this, the plant spreads easily via suckers and has become invasive in some parts of the US, including Michigan, Pennsylvania, and Ohio. The plant does have its uses and provides excellent erosion control on slopes and mountainsides that are affected by this problem.
New Mexico Locust - Robinia neomexicana
In spite of its name, this locust is actually primarily found across the southwestern United States. It can be grown as a tree or a shrub, growing to around 10 feet in height. It features deep purple branches from which stunning floral displays are produced in early spring and summer. Its blooms are pale pink and appear in large, showy clusters, making this a popular ornamental plant. To grow this plant, you should position it in partial sun and water it moderately. It prefers dry sandy soil that is able to drain well.
Which variety of locust tree do you prefer? Cast your vote in the comments, and don’t forget to share this page with other interested growers!