Locust Tree Information – Types Of Locust Trees For The Landscape

Locust Tree Information – Types Of Locust Trees For The Landscape

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By: Jackie Carroll

Members of the pea family, locust trees produce large clusters of pea-like flowers that bloom in spring, followed by long pods. You might think that the name “honey locust” comes from the sweet nectar that bees use to make honey, but it actually refers to the sweet fruit that is a treat for many types of wildlife. Growing locust trees is easy and they adapt well to lawn and street conditions.

The two most common types of locust trees are black locust (Robinia pseudoacacia), also called false acacia, and honey locust (Gleditsia triacanthos) and both types are North American natives. Except for a few thornless honey locust varieties, locust trees have fierce thorns that grow in pairs along the trunk and lower branches. Read on to find out how to grow a locust tree.

Locust Tree Information

Locust trees prefer full sun and tolerate reflected heat from structures. They normally grow quickly, but even a little shade can slow them down. Provide a deep, fertile, moist but well-drained soil. These trees tolerate urban pollution and spray from de-icing salts on roads. They are hardy in USDA plant hardiness zones 4 through 9.

Transplant a locust tree in spring in cold areas and spring or fall in mild climates. Keep the tree well-watered and protected from salt spray for the first year. Afterward, it tolerates adverse conditions. Most locust trees produce many thorny suckers over their lifetime. Remove them as soon as they appear.

You might think because of their relation to legumes, these trees fix nitrogen to the soil. Well, that isn’t the case for all locust trees. The honey locust is a non-nitrogen producing legume and may require regular annual fertilization with a balanced fertilizer. The other locust tree varieties, especially black locust, do fix nitrogen, thus are not in need of as much, if any, fertilization.

Locust Tree Varieties

There are a few cultivars that perform particularly well in home landscapes. These varieties produce dappled shade under their canopies—ideal conditions for a flower border.

  • ‘Impcole’ is a compact, thornless variety with a dense, rounded canopy.
  • ‘Shademaster’ is a thornless variety with a straight trunk and excellent drought tolerance. It grows more quickly than most varieties.
  • ‘Skycole’ is a pyramidal thornless variety. It doesn’t produce fruit, so there is less fall cleanup.

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Robinia pseudoacacia

Robinia pseudoacacia, commonly known in its native territory as black locust, [2] is a medium-sized hardwood deciduous tree, belonging to the tribe Robinieae. It is endemic to a few small areas of the United States, but it has been widely planted and naturalized elsewhere in temperate North America, Europe, Southern Africa [3] and Asia and is considered an invasive species in some areas. [4] Another common name is false acacia, [5] a literal translation of the specific name (pseudo meaning fake or false and acacia referring to the genus of plants with the same name).

Fill a pot almost to the top with high-quality potting mix.

Water the pot thoroughly and allow the soil to settle. Refill the soil to within an inch of the top again.

Plant two seeds, spread well apart, per pot at a depth of ½ inch. Cover the seeds with soil.

Place plastic wrap over the top of the pot. Punch several small holes in the top of the plastic for ventilation.

Put the pot in a spot that receives bright light all day long. Keep the soil moist but not saturated.

Remove the plastic wrap as soon as sprouts emerge. If both seeds germinate snip the smaller sprout off with scissors.

Honey Locust

Family: Fabaceae
Latin Name: Gledistia triacanthos
Common Name(s): Honey Locust, thorny locust

Deciduous or Evergreen: Deciduous
Native Range: Central United States
USDA Hardiness Zone: 3-8
Mature Height: 60-80’
Mature Spread: 60-80’
Bloom Time: May-June
Native to Minnesota: No
Shade Tolerant: No


Honey locust is a beautiful species of shade tree commonly found in Minnesota. Leaves are compound and alternate, with 3-6 side branches each containing many round leaflets. Honey locusts are often dioecious, meaning that trees have either male or females flowers, but it is not always so. Both male and female flowers are greenish-white, fragrant, hanging clusters. Female flowers develop into large, flat, dark brown seed pods, typical of fabaceous plants. The bark is blackish to grayish-brown, with smooth, plate-like patches separated by furrows.

Wild honey locust have large, sharp thorns up to 20 centimeters long. Most landscape honey locusts are a bred variety, G. triacanthos var. inermis, that does not have thorns (inermis means ‘unarmed’). The common name comes from the sweet fruit within the seed pods. Some Native American tribes used the fruit as a sweetener, although it can be a throat irritant. The seeds have also been roasted and used a coffee substitute.

The native range of honey locust ends just south of the Minnesota border in Iowa, but the trees are now often found in the landscape and as street trees, as they grow quickly and can survive in adverse urban conditions, such as hot, dry parking lots.

Honey locust are very susceptible to numerous fungal pests. Interestingly, G. triacanthos var. inermis is highly susceptible to Nectria canker, caused by the fungus Nectria cinnabarina, while the wild, thorned honey locust is not.

Black Locust

The Tree

Otherwise known as false acacia, the black locust tree (Robinia pseudoacacia), is fast growing and hardy. It can grow to a height of around 25 meters and a diameter of around one meter. You may come across some of the very old black locust trees that have a height of around 50 meters and a diameter of 1.5 meters.


The black locust tree produces white flowers that are intensely fragrant and are arranged on axillary, pendulous racemes. You may also come across some black locusts with pink or purple flowers. The flowers are produced in hanging clusters that can be four to ten inches long. Each flower is around an inch in length. Black locust flowers are consumed in some regions.

Leaves and Seed Pods

The leaves are pinnately compound, with a length of around 25 centimeters. Each leaf has nine to nineteen leaflets, that are roughly oval. The leaflets resemble our thumbprints, in size and shape. Each leaf has a single leaflet at the tip. The leaves turn yellowish during autumn. The legume fruit contains seeds. As compared to some other locust species, the seed pods of the black locust are small and light.

Bark and Thorns

A mature black locust tree produces numerous branches, and has a dark and deeply furrowed bark. One of the characteristic features of this tree is the short, prickly thorns that are located at the base of the leaves. The thorns of black locust trees are short, when compared to that of honey locusts. They do not have the branched thorns that are seen on the trunk of honey locust trees.

Though they are mainly grown for ornamental purposes, black locusts are much valued for their hard and durable wood. In some regions, the black locust is cultivated as a honey plant. In other words, the blooms of black locust is a source of nectar for honey bees in that area. Apart from the flowers, the bark, seed pods and every other part of this tree are considered toxic but it is also said that the toxicity can be nullified through cooking. It has also been contended that the tender seed pods as well as the seeds can be boiled and consumed.

Twisty Baby™ Dwarf Black Locust

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Twisty Baby™ Dwarf Black Locust (a.k.a. Lace Lady Locust) is a fun tree that will be a conversation piece in your garden throughout the seasons. This one-of-a-kind specimen sports a wild hairdo of zigzag branches that will draw attention both in and out of leaf. Twisty Baby’s kinky branches are draped with lovely white flowers in spring that smell like grape Kool-Aid—and they’r e edible! You can reach up and pluck a few blossoms to top off the prettiest salad y ou’ll ever have . Plant this tree near your porch, patio, or deck not only to enjoy the flowers’ sweet fragrance, but also to watch the hummingbirds that will swoop in to pollinate them!

Growth Facts

The Story

Black Locust is a scrappy tree native to the Eastern U.S. It often grows on roadside cuts where no other tree would want to grow, somehow getting by on the most meager allotments of soil and water. Its wood is dense and naturally weather-treated, and many a farm has been enclosed by fences built with “Locust” posts. Twisty Baby™ was a chance mutation of the species discovered among a crop of seedlings in New Zealand in 1985. It is sometimes listed as ‘Lace Lady’—two names for the same plant.

The Details

The contorted habit of this dwarf Black Locust will have you in knots! Clusters of fragrant white pea-like blooms appear in spring. Mature foliage is deep bluish-green while newly emerging foliage is apple green - quite fetching! The black bark and brown branches on this twister are extremely showy in winter. A great specimen or focal point in any garden.

Watch the video: Tree of the Week: Black Locust