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What is Black Locust Tree?

The more I learn about the black locust tree, the more I am impressed by it. They grow stunning looking and smelling flowers, and can populate natural areas that have suffered a natural disaster. They can grow in horribly poor soil but are able to make that soil more nutrient-rich for other species.

I don’t want to spoil too much, so just read on to learn a little bit more about this plant superhero, Robiniae Pseudoacacia.

If you’re interested in other tree species, check out 101 Types of Trees to wet your whistle!


Related: Honey Locust Tree | What is a Honey Locust TreeTypes of Locust Trees

Robinia Pseudoacacia

Sometimes known as the “false acacia” due to their uncanny similarities, particularly with their feathered leaves and thorns. They are nearly impossible to tell apart in regions of higher latitudes, apart from slight differences in their flowers.

The black locust tree is part of the robiniae plant family. This is a subfamily of the plant faboideae family, to which the carob tree (ceratonia siliqua L., which is used as a replacement for cocoa powder) belongs as well! Funnily enough, the leguminous peas and beans are also kin to these trees.

The black locust tree is of the deciduous variety and is considered one of the sturdiest hardwoods in all of North America. They are medium-sized, fast-growing, and remarkably resilient to all sorts of different climates. They can live to be up to 100 years old.

What do Black Locust Trees Look Like?

Closeup of a Black Locust tree.


The black locust is a moderately sized tree, usually sticking around heights of 12-30 meters, but sometimes obtaining a height of about 52 meters if the conditions are exactly right (and if they aren’t subjected to a disease or sickness). In mature trees, trunks reach a diameter of up to 1.2 meters.

Bark & Trunk

Their trunks stand very straight and upright and is covered in the bark that is a reddish-gray color. Black locust bark in old trees is deeply furrowed with grooves and ridges that form thin diamond shapes in the bark, and these grooves are usually an attractive orange hue.

Crown & Branches

At the top of a black locust tree, you’ll find a crown that is rather narrow and tends to become rather sparse with age. The branches tend to grow in a meandering pattern, and young branches, when they first sprout, are covered with a beautiful silver down layer. As the tree ages, the down disappears and grows into pale green, reaching a reddish-brown green once it reaches full maturity.


Blossoms of a black locust during summer.

A black locust leaf is a unique blueish green color, that is usually paler on its underside. They are compound leaves. A compound leaf contains many leaflets per leaf. These leaflets are alternately arranged, that is round at the base coming to an indented tip.

Each leaf will have come out of a yellow bud, which emerges in the late spring. Fall foliage is a dull, pale, yellow color. Black locust leaves are attached to the branch by a hairy petiole, which is similar to a twig.

A habit that all other members of the legume family share, the black locust leaflets will fold into themselves at night time and when weather is damp, giving it the title of being a nyctinasty species. This is a way to protect their delicate foliage.

Young trees also come equipped with spines that run along the trunk and branches. This is because the tree has yet to develop a thick, protective bark, and spines are an alternative way for the tree to defend itself.

How do Black Locust Trees Reproduce?


Closeup of a Black Locust tree flowers.

Black locust trees are the most easily recognized by their incredible flowers. They appear in the early summer, are intensely fragrant flowers, slightly resembling the scent of orange blossom. They are large and papilionaceous in shape (meaning shaped like a butterfly). These flowers slightly resemble the shape of an orchid and are incredibly stunning. Its uppermost petal is adorned with a yellow blotch.

The flowers will bloom in May or June and have a very short blooming season. The flowers are arranged in pendant racemes (loose, drooping clusters) and are usually a warm white color, but flowers of pale pink and purple have known to be found as well.

Black locust flowers possess both a stamen and a pistil, meaning that they possess both male and female sexual characteristics. The flowers contain a huge amount of sweet-smelling nectar, to help attract pollinators.

Sometimes when flowers possess both sexual characteristics, they are able to self pollinate — but this is not the case for black locust flowers. Because of the way that the flower is shaped, the male and female parts are separated, and so they need help from pollinators to fertilize the plant. Hymenopteran insects are most commonly attracted to the black locust white flower.


Dried fruits hanging from a Black Locust tree.

Once a tree is fertilized, it will produce fruit or legume, that is flat and very similar to a pea-pod. These fruits contain anywhere between 4-8 seeds, that are dark orange in color. A black locust seed pod usually ripens in the late autumn and will remain hanging until early spring.

Once the seeds drop, the seedlings are able to produce very rapidly. However, the seeds themselves have a rather thick casing, making it so that a small percentage of seeds actually successfully germinate.

Root Sprouting

Swallowtail butterfly on a Black Locust tree flower.

Another way in which the black locust tree is able to reproduce is through the act of root sprouting. The root sprouts are able to emerge from the stump of a black locust tree that has been cut down, or directly from the roots of a tree with a dead trunk.

This is considered as a sexual form of reproduction, and the trees that emerge from an old black locust root system will share the same DNA as the mother tree, like a colony of clones.

Where do Black Locust Trees Grow?

It is up to debate where exactly the black locust tree originated, but it is known that it endemic to certain pockets of the United States. Their native range has been narrowed down to be either in the Appalachian Mountains from Pennsylvania to northern Georgia, or the Ozark Plateau and Ouachita Mountains of Arkansas, Missouri, and Oklahoma. The black locust is a member of the Appalachian mixed mesophytic forest system.

Since then, they have been cultivated en mass and can be found in 48 states, as well as Australia, Canada, China, New Zealand, India, Pakistan, all over South America, all over Europe and Asia, and Africa as well. They tend to grow in the most temperate areas of these regions and are grown mostly and landscaping trees.

What are the Growing Conditions of Black Locust Trees?

Sunlit foggy forest with black locust tree.

Black locust trees will truly grow anywhere where there is soil that isn’t too wet, and where there ample sunlight. They are very intolerant to shade, and that is why they are very typically found in grasslands where there is no canopy competition. Because they don’t grow particularly tall, it’s very easy for them to beat out by taller competition.

Though they are able to grow in all sorts of soils, they prefer soil that is more of the dry side of moist, that is very well-drained — particularly limestone soils. They truly thrive in a pH range of 4.6-8.2, and really do not perform well in soil that is compact, clay, or eroded.

Conveniently enough, when a black locust tree is planted in a sandy area or soil that isn’t very nutrient-rich, it helps to make the soil healthier, which ends up being better for the surrounding plants.

It does this through nodules in its root system that are nitrogen-fixing, which is then fed into the soil. This is like a completely natural foliar spray — which is something you spray on your houseplants when they are experiencing a nutrient deficiency.

Are Black Locust Trees an Invasive Species?

The black locust is unique in the way that it is a species of native vegetation that is invasive in the land that it is native to. It is listed as invasive in the states of Connecticut, Wisconsin, and Massachusetts.

An invasive species is a plant that grows uncontrolled and disrupts the natural ecosystem of a certain area. This usually occurs when a foreign plant is introduced to an unprepared landscape, but in the case of the black locust, it is invasive because it is just too good at growing.

A more polite word for this is a pioneer species. A pioneer species is the first species to repopulate an area that has experienced some sort of natural disturbance — like an avalanche or a forest fire. However, the black locust will also populate an area that is a grassland, essentially changing its ecosystem from a meadow to a forest area.

Another term people use to describe a black locust is as a “weed tree”. Because of the way that it is able to reproduce through root suckers, it is essentially impossible to kill a black locust tree. Cutting the trunk will only allow space for new growth, and removing a root system entirely can prove to be quite difficult.

What Pests Affect the Black Locust Trees?

Like all species of plants on earth, they are bound to deal with some pest or another. Luckily, black locusts have yet to experience a devastating disease that wipes out the population. The black locust is nowhere near being endangered, but it does have to deal with the following pests.

Locust Leaf Miner (odontota dorsalis) – this pest attacks a black locust tree in the spring when it should be placing all of its energy it establishing its spring growth. The locust leaf miner causes first powdery mildew, then browns the foliage, causing a huge stunt in growth in the tree. Sometimes it results in a permanent leaf scar.

Locust Borer (megacyllene robiniae) – much like its name, the locust borer will carve an extreme amount of tunnels into the heartwood of the black locust tree. Not only does this make it vulnerable to other sicknesses, but it also weakens its structure, making it more likely that the tree will be knocked over in a storm.

Witch’s Broom (cholorgenus robiniae) – witch’s broom is a cluster of uncontrolled branch growth that occurs in the sick trees. Smaller branches grow in an unattractive, messy cluster. They grow similarly to which cancerous cells grow in the body — uncontrolled, and completely irregular.

How are Black Locust Trees Used?

Human Use

Black locust trees are valuable for a great number of reasons. They’re an excellent tree to plant in an area that needs help with soil erosion, as their root system is densely clustered and helps keep the earth in place.

The black locust tree is also the source of the world-renowned acacia honey, though the name may be conceiving. It is a very popular honey tree to cultivate.

Closeup of a Black Locust log.

Wood from a black locust tree is considered as being the most durable in all of North America and is used to manufacture fence posts, boats, furniture, flooring, and paneling. An added feature of black locust wood is that it is very resistant to rot in water-saturated conditions.

Another way to prove how resilient black locusts trees are is when they are observed in urban areas. There are impressively un-phased by city pollution, making them a great option for a city street tree.

And finally, this wood makes incredible firewood. The wood itself has a higher heat capacity, its denseness makes it burn for a long time, and it hardly produces any sort of smoke or flame. Black locust wood is the number one choice for people with wood-burning stoves.

Forest Ecology

A bee getting nectar from Black Locust flowers.

In nature, the black locust tree isn’t utilized by a great many species, but it is essential to an important handful. First and foremost, it is very important when a devastated area needs to be repopulated because it attracts other plant and animal species.

It’s fragrant and sweet nectar helps attracts pollinators not only to itself but to other plants in the area that need pollinating as well.

Black locust seeds are eaten by many game birds and squirrels, and specifically the bobwhite quail. Woodpeckers also like to choose a hollow black locust trunk as their home, considering that the locust borer causes heart-rot.


Are black locust trees invasive?

Black locust trees are considered an invasive species in several states. This is because they can tolerate a great many soil varieties, and they tend to populate areas that are without other sun competition. They’re known to turn grasslands into forest ecosystems, effectively reducing grasslands where they are needed.

Are black locust trees valuable?

Black locust wood is incredibly hard, durable, and resistant to waterlogging. They’re an excellent tree to use for timber, and its wood is commonly used in the manufacturing of furniture, paneling, boats, and many other uses.

Do black locust trees have thorns?

Because the black locust tree has developed its mature, protective outer bark, it is equipped with thorns along its trunk and branches in order to protect it from over-foraging and pests.

Do black locust trees bloom every year?

Black locusts are a deciduous tree, meaning that they lose their leaves as the winter months approach, and re-sprout them when spring arrives. Shortly after, flowers will boom, ready to be pollinated.

If a black locust flower does not blossom in a certain year, there is a good chance that it is sick, or there was some conditional issue.

Do black locust trees have deep roots?

Black locust roots don’t grow very deep, as they are not particularly moisture-loving and don’t need to access the water deep in the soil. Their roots tend to grow in shallow clusters.

Does black locust wood make good firewood?

Because black locust wood is so dense, it makes incredible firewood. It is very slower burning, has a very high heat capacity, and doesn’t produce too much smoke or flame. It is the dream variety of wood for people with wood-burning stoves.

Is black locust wood a hardwood?

Black locust is considered the hardest wood in North America.

How do you identify a black locust tree?

The easiest way to identify a black locust tree is through its unique bark, which is gray with a reddish tinge that grows in thin diamond-shaped fissures.

Otherwise, if you catch a black locust tree in the spring, you’ll be able to tell by its creamy white flowers that are slightly shaped like a butterfly, and that smell quite similar to orange blossom.

When do black locust trees bloom?

The flowers of a black locust tree bloom for a very short amount of time, usually only between the month of May and June, and usually not lasting that entire time.

What is the scientific name for the black locust tree?

The scientific name for the black locust tree is robinia pseudoacacia.

What is the difference between a honey locust and a black locust?

Honey locust trees tend to have bark that is far smoother than that of the black locust tree, and honey locust trees have very long and pronounced thorns along their trunk and branches, whereas a mature tree will lose its thorns.

How tall do black locust trees get?

In ideal conditions, black locust trees usually grow to be anywhere between 12-30 meters in height. However, the tallest tree on record reached 52 meters high!

How long do black locust trees live?

If a black locust isn’t subjected to a disease or pest, it can usually live to be 100 years old.

Are black locust trees fast-growing?

Part of the reason why black locust trees are so valuable is that they are very fast growing. They can grow an average of 5 meters a year.

Is black locust good for smoking?

It’s actually one of the best options for smoking. Black locust wood has a super high heat capacity, it doesn’t produce too much smoke and can burn for a long time. Not to mention it has an attractive smell.