Locust trees are known for their hardy nature, durable wood, fragrant sweet spring flowers, and vibrant fall foliage. Two primary species of locust trees are commonly found in North America: the black locust (Robinia pseudoacacia) and the honey locust (Gleditsia triacanthos). These trees are ideal for various purposes such as landscaping and timber production, while some locust tree varieties even boast long, sharp thorns, which add a distinct aesthetic appeal.
In addition to black and honey locusts, several other varieties of locust trees exist, such as the Carob tree (also known as the old world locust tree), Water locust tree, Frisia black locust tree, Twisty baby, Bristly locust tree, and New Mexico locust. Many of these locust tree types can be differentiated by their bark and branch characteristics, including the presence or absence of thorns.
With their versatility and adaptability, locust trees make a great addition to various types of landscapes and environments. Understanding the different varieties of locust trees, their unique characteristics, and their uses can help gardeners and landscape enthusiasts better choose the ideal locust tree for their specific needs.
Types of Locust Trees
Locust trees are known for their hard and durable wood, fragrant sweet spring flowers, and colorful fall foliage. These hardy trees can be found throughout North America and come in various species that have unique characteristics. In this section, we will explore a few of the most common types of locust trees, including black locust, honey locust, New Mexico locust, and bristly locust.
Black locust (Robinia pseudoacacia) is a popular and widely cultivated species of locust tree, typically reaching heights of 40-100 feet (12-30 m) with a diameter of 2-4 feet (0.61-1.22 m). Native to the southeastern United States, this tree is known for its strong and durable wood and sweetly fragrant spring flowers that attract bees and other pollinators. The black locust tree displays distinctive, deeply furrowed bark and pinnately compound leaves that turn yellow in the fall.
Honey locust (Gleditsia triacanthos) is another common species of locust tree, characterized by its large, twisted seed pods, which can reach lengths of up to 18 inches (45 cm). Honey locust trees are native to central North America and are renowned for their adaptability, thriving in a wide range of soil types and environmental conditions. In addition to producing sweetly scented flowers, honey locust tree leaves turn a vibrant mix of yellow and orange in the fall. Some varieties of honey locust trees have long, sharp thorns, while others are thornless.
New Mexico locust (Robinia neomexicana) is a smaller locust tree species that generally reaches heights of 15-20 feet (4.6-6 m) and is native to the southwestern United States. This locust tree is notable for its attractive, pink to purple pea-like flowers that bloom in spring and early summer. The New Mexico locust is drought-tolerant and requires well-draining soil. Its leaves are pinnately compound and turn yellow in the fall.
Bristly locust (Robinia hispida) is a deciduous shrub or small tree that grows to heights of 6-15 feet (1.8-4.6 m) and is native to the eastern United States. Also known as rose-acacia, the bristly locust is distinguished by its showy, pink to rose-purple flowers that bloom in spring. This species is well-suited for use in landscaping as an attractive specimen plant or as part of a mixed shrub border. Bristly locust has compound leaves and prominent, bristly hairs on its stems and seed pods.
Understanding these different types of locust trees can help gardeners, landscapers, and environmental enthusiasts make informed choices about which species to plant and appreciate in their local landscapes.
Characteristics of Locust Trees
Leaves and Flowers
Locust trees, such as Robinia and Gleditsia, are deciduous with green pinnate leaves, which contribute to their lush appearance. The white flowers of these trees are notably fragrant, making them an attractive addition to any landscape. Locust trees bloom in spring, adding a pleasant scent and aesthetic to the environment.
Thorns and Seed Pods
Both Robinia and Gleditsia locust trees are part of the legume family and produce seed pods. Gleditsia, or the honey locust, is known for its large thorns, which grow on the trunk and branches. These thorns can be hazardous, so it’s crucial to consider their placement when landscaping. The seed pods of locust trees are elongated and flat, containing multiple seeds within.
Height and Growth Rate
Locust trees enjoy full sun and grow at an impressive rate. The average height of Robinia, or the black locust tree, is between 40-100 feet (12-30 m), with a diameter of 2-4 feet (0.61-1.22 m). On the other hand, Gleditsia or honey locust trees can reach up to 70 feet in height and display quick growth, growing approximately 20 feet within the first decade. The rapid growth rate and adaptability make locust trees a popular choice for landscaping projects.
While locust trees possess several desirable characteristics, planting them in a suitable location and providing proper maintenance is essential for optimum growth and success. With their fragrant flowers, unique seed pods, and fast growth rate, locust trees are an attractive choice for various landscaping endeavors.
Origins and Distribution
Locust trees (genus Robinia) belong to the pea family (Fabaceae) and are native to eastern North America and Mexico. These flowering trees and shrubs have been cultivated for various purposes, including ornamentals, erosion control, and timber trees. The most common types of locust trees are the black locust (Robinia pseudoacacia) and honey locust (Gleditsia triacanthos).
Originating in the Appalachian Mountains in Pennsylvania, the black locust has since spread to other parts of North America, as well as Europe and Asia. Due to its adaptability to various soil types, it can be found in a range of environments, from woodlands and forest edges to urban landscapes. It is valued for its fragrant sweet spring flowers, fast growth, and hard, durable wood.
The honey locust tree, on the other hand, has a native range that extends from the eastern Great Plains to the southeastern United States. This tree has also been introduced to parts of Europe and Asia, where it is cultivated as an ornamental tree and for its nitrogen-fixing properties. Notably, the common honey locust (Gleditsia triacanthos) is an invasive species in some areas outside its native range, due to its ability to spread aggressively.
In addition to these two popular locust tree species, there are several other varieties native to North America and Mexico, such as the water locust (Gleditsia aquatica), frisia black locust (Robinia pseudoacacia ‘Frisia’), bristly locust (Robinia hispida), and New Mexico locust (Robinia neomexicana). These species contribute to the diverse flora found across the continent and have varying uses and characteristics.
The wide distribution of locust trees is a testament to their adaptability and usefulness in a range of environments. With origins in North America and Mexico, locust trees have become important components in landscapes and ecosystems throughout the world.
Cultivars and Varieties
Black Locust Cultivars
Robinia pseudoacacia, commonly known as the black locust, is a medium-sized hardwood deciduous tree that typically reaches a height of 40-100 feet (12-30 m) and a diameter of 2-4 feet (0.61-1.22 m). Popular for its white flowers, the black locust makes an attractive ornamental tree. One interesting cultivar is the Frisia black locust (Robinia pseudoacacia ‘Frisia’), which features golden-yellow foliage that adds a splash of color to landscapes.
The Purple Robe black locust (Robinia pseudoacacia ‘Purple Robe’) stands out for its beautiful purple flowers, providing a unique aesthetic to any garden. Additionally, the New Mexico locust (Robinia neomexicana) is another variety within this genus, offering an alternative for those looking for diversity in their locust tree landscapes.
Honey Locust Cultivars
Gleditsia triacanthos, or the honey locust, is another prevalent locust tree type native to North America. Its name comes from the sweet taste of its pods and the tree’s nectar-rich flowers, which serve as an excellent resource for honeybees. Several honey locust cultivars exhibit distinct features and unique characteristics.
The Imperial honey locust (Gleditsia triacanthos ‘Impcole’) is one such variety, known for its dense, dark green foliage and more compact, rounded shape. Similarly, the Skyline honey locust (Gleditsia triacanthos ‘Skycole’) is valued for its uniform branching structure and pyramidal form, making it an excellent choice for urban landscaping.
For those interested in thornless options, cultivars like the Thornless honey locust (Gleditsia triacanthos ‘Inermis’) and the Shademaster honey locust (Gleditsia triacanthos ‘Shademaster’) offer landscapes an attractive and less hazardous alternative. Finally, the Blue acacia (Gleditsia triacanthos ‘Blue Acacia’) presents an additional option, with its bluish-green foliage providing a unique visual appeal.
In conclusion, both black and honey locust trees offer diverse cultivars and varieties to choose from, ensuring that landscapes can benefit from these attractive and functional trees in numerous ways.
Locust trees are known for their adaptability to various environmental conditions. This section will examine their tolerance to different soil and drainage conditions, as well as their resilience in the face of drought, salt, pollution, and heat.
Soil and Drainage
Locust trees can tolerate a wide range of soil conditions, including poor soil with low nutrient levels. They prefer well-draining soil but can also adapt to slightly wet or compacted soils. Locust trees can also tolerate a variety of pH levels, growing in both acidic and alkaline soils.
Drought and Salt Tolerance
Drought tolerance is a notable characteristic of locust trees, with species like the honey locust (Gleditsia triacanthos) being particularly resilient. These trees can withstand long periods without rainfall and can survive in areas with low water availability. Additionally, some locust tree species can tolerate moderate levels of salt in the soil, allowing them to grow near coastal regions or in areas with saline soils.
Pollution and Heat Tolerance
Locust trees have shown a strong ability to withstand urban pollution, making them suitable choices for planting in cities and other polluted areas. Their hardy nature allows them to withstand a variety of environmental stressors, including air and soil contamination.
Heat tolerance is another important feature of locust trees. They can adapt to high temperatures and still continue to grow and thrive, making them suitable choices for regions with hot climatic conditions.
Practical Uses of Locust Trees
Landscaping and Shade Trees
Locust trees are popular choices for landscaping purposes due to their fast-growing nature and ability to provide ample shade. As shade trees, they are especially useful in areas with hot summers, offering a retreat from the sun and helping to cool outdoor spaces. The trees’ attractive foliage and fragrant flowers also make them suitable for use as accent plants in gardens and landscapes, adding visual interest and color to the environment.
Timber and Fence Posts
The wood of locust trees, particularly the black locust, is hard and durable, making it an excellent material for furniture, timber, and fence posts. Its resistance to rot and insect damage allows for long-lasting fence posts requiring minimal maintenance. Additionally, the wood’s fine-grain and high-density properties make it a sought-after material for furniture making, providing both strength and aesthetic appeal.
Locust trees, especially the black locust, serve as a valuable source of nectar for bees. The trees’ sweet and fragrant flowers attract bees, which in turn produce honey from the collected nectar. This makes locust trees a favorite honey plant among beekeepers and an essential element in boosting honey production, contributing to both the environment and the economy.
Invasive Species Control
While some locust tree species can become invasive, they can also serve as a tool in the control of other invasive species. For example, the black locust’s fast-growing and hardy nature enables it to outcompete certain invasive plants, providing a natural method of controlling unwanted growth and protecting native species. However, it’s essential to monitor locust tree growth to prevent them from becoming invasive themselves.
Pests and Diseases
Locust trees are susceptible to various insect infestations, which can potentially harm the tree’s health. Some common insects that affect locust trees include:
- Eriophyid mites: These tiny insects can cause leaves to curl and disfigure, leading to reduced foliage and tree vigor.
- Honeylocust spider mites: These pests feed on leaf tissue, causing discoloration and damage that can potentially affect the tree’s overall health.
- Honeylocust pod gall midges: These insects can cause the formation of gall-like structures, reducing the aesthetic value of the tree and potentially causing twig dieback.
Locust trees may also experience various diseases that can impact their well-being. Some prevalent diseases include:
- Canker: This disease presents as sunken, dead areas of bark, which can result in dieback, reduced foliage, yellow foliage, premature fall coloration, and early leaf drop. Cankers can potentially girdle the stem and kill the tree. To control canker diseases, it is essential to prevent wounds and stress while promoting tree vigor.
- Verticillium wilt: This fungal disease enters the tree through the roots and can cause severe stress, leading to wilted leaves and overall decline in health. It is crucial to monitor for early signs of this disease and apply proper preventative measures.
- Root collar rot: This disease infects the base of the tree, potentially causing significant damage and even tree death if left untreated.
In addition to the mentioned pests and diseases, locust trees may also produce unwanted growth, such as suckers, from the base of the tree. Regular pruning can help control sucker growth.
It is essential to note that while the honeylocust tree has some toxic properties, they are generally not considered highly toxic to humans or animals. However, sensitive individuals or certain livestock may experience adverse reactions if locust tree parts are ingested. As a precaution, it is advisable to keep children and pets away from consuming any part of the tree.
Frequently Asked Questions
What are the main differences between honey locust and black locust trees?
Honey locust trees (Gleditsia Triacanthos) and black locust trees (Robinia pseudoacacia) are two distinct species of locust trees. Honey locusts are known for their compound leaves and small, greenish-white flowers which produce long, twisted seed pods. Black locust trees have larger compound leaves, showy white flowers, and smaller, flat seed pods. The wood of black locust is harder and more durable than that of honey locust.
Which locust tree varieties are thornless?
Thornless varieties of locust trees do exist, providing a safer option for landscaping. Some known thornless varieties of honey locust include the ‘Imperial’, ‘Shademaster’, and ‘Skyline’ cultivars. Thornless black locust trees are less common, and one such variety is the ‘Inermis’ cultivar.
How does sunburst honey locust differ from other locust trees?
The Sunburst honey locust (Gleditsia triacanthos ‘Sunburst’) is a cultivar of honey locust known for its distinctive golden-yellow foliage that appears in spring and gradually turns green throughout the summer. This variety is also thornless, making it an attractive and safe option for landscaping and gardens.
What is the difference between purple robe and honey locust trees?
The Purple Robe black locust tree (Robinia pseudoacacia ‘Purple Robe’) is a cultivar of black locust, known for its striking, rich purple flowers instead of the typical white flowers of the species. This sets it apart from the honey locust tree, which has smaller, greenish-white flowers and is a different species altogether.
What are the common features of locust trees?
Locust trees are hardy and adaptable, known for their durable wood, fragrant spring flowers, and colorful fall foliage. They typically have compound leaves and produce distinctive seed pods. Many varieties of locust trees also have long, sharp thorns, although thornless varieties do exist.
Which locust tree species are native to North America?
The black locust (Robinia pseudoacacia) and honey locust (Gleditsia triacanthos) are both native to North America. The black locust is originally from the southeastern United States, while the honey locust is native to the central and eastern regions of the United States.