Locust trees belong to a family of flowering plants called Fabaceae, they are fast-growing. The locust trees have good hardwood and extraordinarily colorful flowers, which bloom in spring. The locust trees generally grow in the eastern part of the USA.
The locust tree grows very long and has sharp thorns. These thorns are sturdy and were used as nails a long time back. These thorns are a real hazard and deterrent.
The locust tree has many natural varieties and cultivars, and all of them belong to one of the two genera of the locust tree, namely Robinia or Gleditsia. One of the most famous representatives of the Robinia genus is the Black Locust tree. The famous Honey locust tree belongs to the family Gedistisia. Interestingly locust trees grow as shrubs also, apart from growing long.
Identifying a locust tree
The most prominent identification feature of a locust tree is its unique thorns, the pods, the sweetly fragrant flowers, and the leaves.
In the spring, you can see sweet fragrant pea-shaped flowers hanging in clusters all over the tree. The flowers are generally white or pink in color. However, depending on the species, differently colored flowers may also bloom. The tree has bipinnately compound leaves in the shape of wings. The overall size of the leaf is 6 cm to 14 cm (depending on the variety) and is broken down into leaflets twice (that is a bipinnate leaf). The main leaf stem branches into smaller leaf branches, which have tiny leaflets on them. The leaflets are just 1.5cm to 2cm and round to oblong in shape. The leaves are dark to light green, depending upon the species and the variety.
Most of the locust trees have pods since they belong to the pea family. The largest of the pods is about 18 inches long, and some species have smaller pods ranging a couple of inches in length. The pods carry the seeds and are flat in shape.
A very prominent feature of the locust tree is the long and menacing thorns. These thorns are very sharp and can bruise very severely. These are typically found on the trunk, branches, and the base of the leaves. It is a kind of protective and defense mechanism of the locust tree against intruders.
There are a large number of species of the locust tree. Apart from the general identification marks, every species has its peculiarities and unique identities.
Some of the prominent varieties and their peculiarities are;
Honey Locust (Gleditsia triacanthos)
It is the largest of the locust tree variety, which can go up to 80 feet in height. The flowers are greenish-yellow in color and not so attractive as other locust trees. The flowers bloom in the late spring and early summer. It has the biggest and the fiercest of thorns. They come in branches and can be 20 inches long. The pods of the tree are largest in size ranging from 10 inches to 18 inches. Being that long and flat, often, the seed pods also get twisted. The tree derives its name, honey locust tree, because of the sweet taste of these pods. The USDA suggests zone 4 through 9 as being the most suitable for this species.
Black Locust (Robinia pseudoacacia)
It has a beautiful cluster of white and fragrant flowers, about one inch in size, that blossoms in the late spring. The black locust has smaller pods: sized from two to four inches. The pods have a leathery texture and are dark red to black in color.
Next to the honey locust, this is the tallest of the locust tree with a height of 70 feet. The thorns are present where the leaves join the stem. In the younger and immature black locust tree, the thorns are present on the trunk of the tree also. But these are much smaller in size. As the tree matures, these thorns vanish or reduce.
The bark of the black locust is dark grey in color with deep furrows. The inner part of the furrows is orange-red, and hence the bark of the black locust appears orangish-red sometimes. It is suitable to be grown in zone 4 through 8.
New Mexico Locust (Robinia neomexicana)
It is relatively a short tree with a height of around 6 to 15 feet. But it has the most beautiful blooms of sweet fragrance pink to red flowers in a cluster. These flowers appear in late spring to early summertime. It also has small pods from 2 to 4 inches. If you look closely you can see narrow wings on the sides of the pods to help dispersal by air.
The tree generally appears a little greyish in color due to the presence of short hairs on the leaves and branches. It grows well in zones ranging from 4 to 8.
Bristly locust (Robinia hispida)
It is the shrub variety of the locust tree and grows to a height of about 6 to 10 feet. The bristly locust is as wide as tall. It has stunning rosy pink to red flowers, and these possess a delightful fragrance. The pods are reddish-brown with bristles on them. The bristly locust is suitable for little warmer zones from 6 to 11.
How do you tell a black locust from a honey locust?
The difference between the honey locust tree and the black locust is evident in the flowers, leaves, pods, and the thorns.
The flower of the honey locust tree is greenish-yellow in color and is not so beautiful or striking.
The Black locust tree has very fragrant and beautiful white flowers.
The honey locust tree has light green leaves, and it has no leaflets at the tip of the leaf.
The leaves of the black locust are much darker in the shade and have leaflets right till the tip of the leaf.
The pods of a honey locust tree are enormous in size. It measures 10 -18 inches. And they are all curled and twisted.
But the black locust pods are much smaller, ranging from two to four inches. Though it has the typical curl of the pod but is not that twisted.
The locust tree has big thorns and thorn branches, which can be very sharp and nasty.
The black locust tree has thorns at the base of the leaf where it joins the stem. In the young black locust, tree thorns develop on the tree trunk, but as the tree matures, the thorns go away.
The honey locust tree has furrowed bark
The black locust has a smooth bark.
Which locust trees have thorns?
All native species of the locust tree have thorns. And the honey locust has the most dangerous and biggest of the thorns. But one variation of the honey locust tree, known as Gleditsia triacanthos f. inermis, grows without thorns. However, some offsprings of the thornless locust tree grow with thorns.
The thornless variation, despite being a mystery, for the botanist and horticulturist, is a delight for the owner. Gleditsia triacanthos f. inermis, is a type of thornless locust tree that is very popular for growing in residential properties, parks, and public places. It generally grows up to a height of 30 to 70 feet with an equivalent spread. It also grows very fast with a growth rate of over 24 inches/year.
The locust tree has beautiful flowers and captivating beauty. Locust tree hardwood is said to have built the USA. However, because of the ferocious thorns, growers fear to plant them. Horticulturists have developed the cultivars from the thornless locust trees. They have genetically engineered the plants to reduce the height from 70 feet to around 40 feet, which becomes manageable for home growers. One such cultivar variation is known as the ‘Sunburst.’ The ‘Sky Cole’ and the ‘shade master’ are some of the other cultivars which have no thorns.
Long time back, the sharp and hardy thorns were used as nails. For the trees, it was a great defense system against the intruders. But in recent times, there is no use of thorns either for the plant or the grower. So a Locust tree without thorns is not short of anything. On the contrary, such a cultivar is more comfortable to grow and maintain.
Along with the leaves and twigs, the thorns also fall down from the tree. And these thorns are a real nuisance when you walk under a locust tree. They can very easily penetrate the footwear and hurt the feet real bad and severe.
What is the lifespan of a locust tree?
The average lifespan of the locust tree is around 100 years. The honey locust tree grows very fast, but lives for about 120 years. The black locust tree has a lesser life span of around 100 years.
The imperial honey locust tree has a lifespan of 70 years, but with the right living conditions, it can live a little longer.
Full sunlight for 6 hours will help keep the locust tree healthy. The soil should be moist but well-drained. In the initial growing years, it is necessary to water the tree often to keep the soil moist.
Trim and prune the locust tree frequently to remove the diseased or damaged branches and twigs.
If you are planting the locust tree for commercial purposes, i.e., for its hardwood, you should plant them in batches with a few years gap between them. It will ensure a continuous supply of wood from your forest or timberland.
Are locust trees messy?
Yes, the locust trees are messy during the fall. It has lots of things to drop. Once the flowering season is over, it drops the dried flowers in vast quantities. Similarly, in the fall, the leaves also drop down. Though they are small in size, being too many, they cover the ground and make it dirty. Being small and light, they get blown off all over the place.
The twigs and the branches also keep falling. The most dangerous dropping of the locust tree is the thorns. They hurt bad and are a cause for concern.
You should consider this fact before planting the locust tree in your residential premises. Do not plant them close to your gate or the driveway. Keep them away from any walkways and all those places where children will have access. It is to protect them from the painful thorns.
It is much better to plant the thornless varieties in residential premises. Various cultivars of smaller heights are also available. You can have a locust tree with its beauty sans the mess and the danger.
You will have to devote time and attention during the fall to take care of the mess. But if you plant the locust tree in the forest land, you just have to worry about the thorns. The leaves and the flower will decompose and mix with the soil in due course of time.
Do locust trees have deep roots?
Locust trees have reasonably deep roots.
Many experts feel the locust tree has a tap root system that goes very deep inside the ground. But a large group of botanists and horticulturists have the opinion that the locust tree has a hearty root system. The heart root system is a combination of the taproot and the fibrous root system.
The main root of the locust tree goes down up to 20 feet. But in addition to this tap root, it has lots of fibrous branches with spreads far and wide. This kind of root system is known as the heart root system.
The shallow spread-out fibrous roots make the locust tree resistant to dry soil to some extent. We really cannot classify it as a drought-resistant tree. But these fibrous roots can pick up the surface and superficial moisture and humidity and survive for some time, even if the water has not reached the taproot.
The prominent and robust taproot needs slow and deep watering. But the soil needs to be well-drained; otherwise, root rot will destroy the tree.
Do locust trees have fruit?
Botanically speaking, the locust trees do have fruits in the form of pods. Locust tree is a leguminous tree that always has fruit in the form of seed pods. It is not a fruit conforming to the common understanding of fruit, but the pod is the fruit of the locust tree.
The pods mainly have seeds, with very little pulp or any other material in it. The pods of the honey locust trees are edible and sweet in taste. The pods of other locust trees are not edible.
Do all locust trees have pods?
No, not all locust trees have pods. The male locust trees have flowers, which help pollinate the flowers of the female trees. But they do not have any pods, because no fertilization takes place on the male tree. Similarly, the cultivars ‘Sunburst’, ‘Skycole’ and ‘Shade master’ do not have pods.
Most of the locust trees do have pods, as they carry the seeds for the further propagation of the plants. But not all locust trees have pods.
The honey locust tree has big pods that carry 12-14 seeds and are edible. Animals, like cattle, deer, rabbits, and squirrels, love eating it.
The black locusts have smaller pods of about 4 inches, but it contains up to 14 seeds. These pods are not edible.
The Mexican locust tree and the bristly locust tree have smaller pods around 2 inches long with hairs on them.
Similarly, the horticulturists have developed various cultivars that do not produce thorns and pods. The absence of thorns and pods reduces the litter, and it becomes suitable for planting in residential premises.
The Black locust and some other locust trees are considered invasive. The invasion here is not about roots destroying roads and construction. But, the trees propagate so fast and aggressively that it takes over the region from the native plantations. Other trees dwindle in numbers. Locust tree is known for this kind of invasion.
The trees cannot self-propagate without the pods. So, in a way, invasive aggression is controlled.
Are locust tree pods edible?
Only the pods of the honey locust trees are edible.
It has a pleasant sweet taste, and along with humans, the animals also love to eat it.
On the contrary, the pods of the Black locust tree are very toxic to humans. It is always better to grow podless trees in the residential premise to prevent accidental eating of the pods by animals or humans. Even the pets are safe that way.
Legend says that John the Baptist survived his travel in the wilderness by eating the honey locust pods.
Why are locust trees dying?
The locust tree dies prematurely because of pests and diseases like a canker, leaf miner, etc.
The locust trees are susceptible to lots of disease and attack by the pest. Some of the most common reasons for the premature death of the Locust trees are;
It is a very dangerous fungal infection. If infected, the leaves start turning yellow and brown, and they fall off. The infected twigs and branches also get stifled and fall off the tree. If not controlled, the canker will destroy the whole tree. The trees in the forest get infected, and if it goes unnoticed, not only one tree but many trees get infected and die eventually.
If you notice a canker on your tree, prune off the infected branches with disinfected cutting tools. And burn off these infected tree parts far away from other trees. If the canker reaches the trunk of the tree, it will turn fatal. So, you must cut off the tree if the trunk gets infected.
The best way to prevent this infection is to keep the tree healthy with strong immunity. Except for the rainy days, water the locust tree once in ten days. Spray the right amount of water under the canopy of the trees in the early spring. The soil has to be kept moist. Fertilize the tree with a standard 10-10-10 mixture during the early spring. That will ensure proper and healthy growth during the spring season.
It is caused by the fungal spores that enter the branches and the twigs through the cut and pruned wounds. The infected area becomes pulpy and rotten. It can spread to other branches also. Hence the best thing to do is cut the infected branches immediately.
Cutting off the infected branches and twigs as soon as possible is the immediate action to take. In the long run, prevent such infection by boosting the immunity of the tree with sufficient water and nutrient-rich fertilizer. Ensure that the tree gets adequate sunlight. Remove any obstructing branches of other trees.
These insects damage the twig or the branch that they infect. The Bark beetle and the round-headed borer enter into the branch through the tip and eat away the branch to destroy it. Very frequently, they go right up to six inches deep, and the branch hangs down dead and listless.
These pests generally attack a weakened or sick tree. So, check the tree for some other disease as well. Prune and trim the infected branches and parts of the tree.
The larvae of the carpenter worm, drill their way into the branches to create a hollow tunnel. This tunnel consequently weakens and kills the branch. This worm can also spread to other branches and ultimately destroy the whole tree. In this case, too, it is best to cut off the infected branches. Nurture and feed the tree well so that it can fight such insect attacks.