Locust trees are one of the hardiest, easy to maintain, and common shade plants in North America, Europe, and some regions in Asia. It comes in two main types which might have confused you in one way or another.
You might be interested in the locust tree because of its decorative and shade value. But you have to understand that not all could be planted in your lawns, not all pulps are edible and not all would bloom flowers or produce seeds.
For whatever purpose you have in mind, it is essential that you get to know the types of locust trees. In this post, you will get to know some of the most common locust tree cultivars per type. Other FAQs about the locust trees are also featured here.
Why is it called a locust tree?
First of all, locust trees are not where locus insects swarm. There is no exact evidence to the endemicity of the locust tree but bible historians reveal that the widely referenced locust which sustained prominent bible figures such as John the Baptist and the other apostles as they traveled around to preach was not really insects but either locus trees or carob trees. These two trees have an uncanny resemblance to each other.
Etymologically speaking, Robinia pseudoacacia which is the scientific name of black locusts gets its name from Jean Robin, the person whose garden is where the first locust tree was grown in Europe and false acacia due to the tree’s similarity to the acacia tree. Acacia comes from the Greek word akis which translates to thorns.
History tells us that it was the 17th-century Christian-American immigrants in Europe who named the Robinia tree a locust tree citing its characteristics from the bible. They aligned the descriptions of John the Baptist of the three where he ate from.
The same immigrants also divided black locusts and honey locust trees.
What are the different types of locust tree?
There at least 20 recognized cultivars of locust trees but there are two major types when it comes to this tree.
Basically, it is divided between black locust trees (Robinia pseudoacacia) and honey locust trees (Gleditsia triacanthos). These two divisions are endemic in the whole North American region.
These two are differentiated by the thorns on the barks and branches. Black locust trees have thorns while honey locust trees are mostly thornless.
Black locust tree
These locust trees are native to the North American region and are considered as one of the most common variants of locust trees. Aside from their known multiple uses, they are also easy to cultivate because they could withstand low-quality soils and droughts.
They are commonly seen in woodlands and in riverbanks. They are unique for their leaf gaps and make excellent shade as they grow from 40-60ft.
They are also known for their thorny branches and barks. Most importantly, black locust trees can be toxic to humans and animals when some parts of it are ingested or contact with its toxic parts are exposed to the mouth.
Uses of black locust trees
Being hardwood trees that grow tall and thick, the following are the uses of black locust trees.
- Timber: black locust trees produce high-quality timber used in manufacturing fences and other carpentry services.
- Honey production: they bloom dense clusters of flowers that attract bees, among others. This is the reason why black locusts are planted in areas with robust honey production industries.
- Firewood: since their wood is sturdy, black locust woods are hard to burn to make them efficient sources of firewood.
Types of black locust trees
1. Frisia black locust (Robinia pseudoacacia ‘Frisia’)
It is a fast-growing black locust tree growing at a height of 30-50ft tall with a spread of 30-40ft. It grows upright and has leaf gaps casting ample light for other plants in the lawn to grow. Shoots of this tree are thorny with deep red color.
It sports rich green foliage in the spring, yellow-green foliage in the summer, and golden yellow in the fall. It is drought tolerant and will produce fragrant white flowers from late spring to summer.
2. Purple robe black locust (Robinia pseudoacacia ‘Purple Robe’)
It is considered as one of the most beautiful locust trees because its leaves change in every growth stage. In its blooming stage, bright green with purple tinge foliage will emerge.
At its mature stage, bronze-colored leaves form. It also blooms in dense clusters of bright pink and purplish flowers from spring to summer. It is a popular lawn and landscape choice for homeowners.
3. Twisty baby black locust (Robinia pseudoacacia ‘Lace Lady’)
It can be cultivated either as a shrub or tree. It has a compact shape and grows at 20ft. When grown in pots, it grows at a height of 5ft. It gets its name from its twisted/contorting limbs giving it a distinguishable appearance.
Winter pruning makes it more twisty. It has dark green foliage which contrasts well with its dense, fragrant white flowers blooming during summer.
Honey locust tree
They are known fast-growers and could really grow massive in size (100ft in the wild and 40-70ft when cultivated).
They are also very hardy to inferior quality soils and poor environmental conditions.
Their spread is also wide making them a common sight in parks. Aside from this, their presence in public areas is not a problem because their leaves are tiny and do not need to be collected or will most likely not block drainages.
Uses of honey locust trees
Honey locusts are also hardwoods but aside from providing wood supply, they are also beneficial for other things. Here are the main uses of honey locust trees.
- Food source: Its seedpods actually contain sweet and chewy pulps that are edible. These pulps are used in traditional cuisine and medicines. At present, these pulps are still used in the production of herbal tea and the fermentation of beer. The seed pods as a whole are harvested for livestock feed.
- Timber: Honey locusts also have durable wood. It is cultivated more for crafting furniture than in carpentry, unlike black locust trees.
- Landscaping: Honey locusts are more common landscape trees. It is good in erosion control and in providing shade. But because of its tendency for overgrowth, it is considered as invasive in some regions.
Types of honey locust trees
4. Bristly locust tree (Rose acacia)
It is also known as the Rose Acacia or the Moss Locust. They are deciduous shrubs growing to an average of 8ft only. They are aggressive growers, however, and are considered as invasive shrubs in Ohio, Washington, and Michigan.
It gets its name from its bristly stems. It blooms very fragrant white flowers that are attractive to bees and other insects. It thrives in loamy, moist soils with a high salt level. They are good at erosion control though.
5. Imperial honey locust tree (Gleditsia triacanthos ‘Impcole’)
It is considered as one of the most popular variants of shade trees good for lawns and streets. It also has a ferny structure in an overall yellow-green tinge.
It grows at 30-40ft and spreads to up to 35ft. It can withstand a wide range of environment types and soil conditions. It specifically loves full sun and moist, well-draining soils. Its wood is good in woodwork and crafting furniture.
6. New Mexico locust tree (Robinia neomexicana)
It is native to the southwest region of the US. It is cultivated as both a shrub or a tree depending on the type of soil and the amount of sunlight it would get.
It grows at an average of 10ft and 7ft of shade. It is distinguishable for its large, thick branches and masses of flowers blooming from spring to summer.
7. Purple Robe locust tree (Robinia pseudoacacia ‘Purple Robe’)
It is a known shade tree that can tolerate inferior growing conditions. It is, however, not recommended for home lawns because it has an invasive tendency, it is thorny and with relatively weaker wood than the others.
Summer or fall pruning is recommended for this tree for it to maintain its pyramid-shape. It could grow to up to 20ft and could tolerate drought and high salt soil content.
8. Ruby Lace thornless honey locust (Gleditsia triacanthos f. inermis ‘Rubylace’)
It is very attractive with its ferny leaves and overall weeping foliage. It thrives in dry and warm seasons only and does not bloom flowers.
It is a decorative lawn tree growing at 25ft. It gets its name from its ruby-red foliage in the spring and summer that turns bronze-green or golden yellow in the fall.
9. Skyline honey locust tree (Gleditsia triacanthos f. inermis ‘Skycole’ Skyline®)
It has a unique ferny structure growing to up to 45ft with a spread of up to 25ft. It has an upright growing habit, making it a loved tree for parks and streets. Aside from this, it is low-maintenance.
It only needs ample sunlight and winter pruning. It is tolerant of all kinds of soil pH levels. Its seeds are sweet and chewy and it will bloom yellow-green flowers. Its trunk is thorny, however.
10. Sunburst honey locust tree (Gleditsia triacanthos ‘Suncole’)
It is native to the midwest US growing in moist and cold locations. It is a fast-growing shade tree following an arching habit. It reaches a height of 30-50ft and a shade of 30-35ft.
It has leaf gaps providing dappled light to lawn plants. Bright yellow leaves will appear in the spring fading into pale green over fall. It needs winter pruning and deep watering. It boasts a good shade and accent plant that is generally disease and deer resistant.
11. Shademaster honey locust tree (Gleditsia triacanthos ‘Shademaster’)
It is distinguishable for not having thorns and boasts its fast-growing habit. They grow at an average of 50ft.
They do not bear fruits, hence, no seed pods. They are considered as one of the easy-maintenance locusts. They sport green foliage in spring that will turn yellow in the fall. They also feature yellow flowers with mild fragrance blooming from spring to summer.
12. Thornless honey locust (Gleditsia triacanthos form inermis)
It gets its name from not having thorns in its bark and twigs, unlike typical native honey locust trees. It is durable and adaptive, tolerant to drought and salt.
It has ferny leaves that are deep green in spring and turns golden yellow during fall. It is a common sight in cities and suburban landscapes.
Locust tree pods
Locust tree pods contain seeds that can be harvested to plant new locust trees. They are usually seen hanging on the thick branches of the tree in between spring to early fall.
Inside the tree, pods are seeds that differentiate black and honey locust trees. Black locust seeds are considered inedible and poisonous to humans and animals. In contrast, honey locust seeds have sweet, edible pulp.
The pulp is harvested to be ground as flour or to be fermented as beer. Tree pods of honey locusts also provide a stable food source for wildlife (rabbit, squirrels, deer, among others).
Locust tree insects and diseases
Insect infestation among locust trees usually happens during late spring. Brown or yellow spotting on the leaves imply bug infestation. Locusts are also the favorite of tree borers, laying eggs in locust tree barks especially during summer.
Blister beetles also target locust trees and they do so in droves or colonies. When you see an ash-gray substance in the locust tree barks, it is already clear evidence of Blister beetle infestation. Other insects feasting on locust trees would be mites, pod gall midges, and cottony maple scales.
Although hardwoods, locust trees are also susceptible to various kinds of diseases.
First off, locust trees are vulnerable to fungi buildup specifically verticillium wilt which affects the tree through its roots. It leads to wilting branches and leaf curling on one side of the tree.
The formation of cankers is also a serious problem for these trees. Dead spots in the bark are evidence of canker disease and this leads to wood decay.
Lastly, locust trees are susceptible to wetwood disease caused by bacteria buildup. When locust trees contract this disease, the bark becomes consistently wet or oozing with slime. The tree color also turns yellow or brown.
Locust tree losing leaves in summer
As to other moist-loving trees, locust trees lose leaves in the summer because of too much heat or too much stress. It means that the soil where it is planted no longer supports its needed moisture.
Dropping leaves are usually yellow with no evident spots. Even with good irrigation, highly humid air leads to leaf dropping too. To prevent this from happening or to adapt locust trees in hotter climates, annual pruning must be done.
Frequently Asked Questions
What is the lifespan of a locust tree?
There is a significant difference in the lifespan of black locusts and honey locust trees. Black locust trees are fast-growing but are considered as having a medium lifespan of 80 years. In contrast, honey locust trees have longer lifespans stretching from 100-120years.
How do you know when a locust tree is dying?
Since we have already discussed the insects infesting locust trees and the diseases that it could contract, you have to look for four signs indicating a dying locust tree.
- Abnormalities in the bark: having deep cracks and holes along the tree bark is not a good sign.
- Decay: typically, decay starts inside. This is caused by tree borers, fungi, and bacteria.
- Dead branches: locust trees are hardwoods so dead branches are typically revealed when they become dry and brittle.
- Leaf discoloration: locust leaves never turn brown and their fall colors are easily distinguished. So when leaves start turning browning and spots are all over it, you should start worrying about your locust tree.
How do you stop a locust tree from spreading?
Locust trees can be a growing problem, especially when grown as shrubs. As a matter of fact, locust trees have been tagged as invasive in some US states like Michigan, Oregon, and Washington.
They have sturdy, rhizomatic roots that easily follow a long stretch. While they are good at controlling erosion, they could also be a problem for critters in riverbanks as they block the passage or flow of water in the river. With these, it is not a wonder why some would want to stop the spreading of locust trees.
There are two ways to stop a locust tree from spreading. One, their aggressive growth can be stopped through repeated cutting specifically during the growing season. New stems should also be cut during this time. This process should be repeated for many years to finally stop them from spreading.
Two, you can use potent herbicides. Cutting the tree horizontally during late summer and early fall for the herbicide to trickle down to the roots help in stopping the locust tree from spreading. This is not a one-time big-time thing, however. Like the first step, applying herbicides must be done twice a year for at least three consecutive years.
Are locust trees poisonous to humans?
Not all locust trees are poisonous to humans. Only the black locust trees contain a toxic substance called toxalbumin.
It can be fatal when ingested although researchers establish that being poisoned due to contact with black locust trees are rare.
The toxic component of black locust trees is concentrated in the bark, branches, and even leaves of. When ingested, they cause severe stomach pain, vomiting, and diarrhea to children, pets, and even livestock.
We have pretty much-covered everything that you should know about locust trees. The two main types are black locust trees and honey locust trees. Both are good shade trees but have stark differences.
For one, black locusts can be toxic to animals and humans. But at the same time, black locusts provide timber, firewood and their more fragrant flowers attract bees for honey production.
In contrast, honey locust trees are cultivated either as shrubs or trees and are cultivated for woodwork, especially in crafting furniture. Overall, locust trees are dependable trees and come with many uses beyond being decorative. This is the reason why they remain to be widely cultivated as ornamental shrubs and or grown fully as trees for their many uses.