Black Locust - Robinia pseudoacacia - Zone 4
Black locusts are a species of extremely versatile medium sized deciduous trees belonging to the pea family. Along with providing one of the most beautiful and edible flower shows imaginable, they can provide many more tangible benefits including erosion control and land rehabilitation by way of their nitrogen fixing capabilities. Juglone tolerant.
Black locusts are fast growing natives of eastern North America. Though their native range is believed to be limited to a couple of small mountainous patches in the eastern United States, their vigorous and resilient nature has fueled their proliferation across most of the continent as well as parts of Europe, South Africa, and Asia. These trees can reach heights of 25 metres and trunk diameters of 60 cm with lifespans usually averaging about 100 years. They will generally develop narrow and open crowns and very extensive roots. The leaves are pinnately compound with 7-20 oval leaflets, about 2 inches long with a bluish-green hue on top and a pale underside. Thorns grow in pairs where the leaf meets the branch. The bark is smooth and brown when young becoming gray/black when mature. The seeds are small and flat and borne in 2-4 inch long pods, about 4-8 seeds per pod. They are toxic to humans. Black locusts produce large clusters of beautiful and intensely fragrant drooping white flowers in May/June and for about two weeks out of the year the tree is absolutely breathtaking. They can adapt to and thrive in very poor environmental conditions and will grow in anything but heavily waterlogged soil. They can handle pH between 4.6 and 8.2 and are highly resistant to pollution. Sunlight is very important for these trees, given a significant amount they will flourish but they are unable to compete when shaded out and will surely succumb.
Black locusts are eminently useful trees from both a practical and ornamental standpoint. As ornamentals their flower show is hard to match providing both visual and olfactory gratification. These same flowers also offer the benefits of being deliciously edible and an excellent and beloved source of pollen for bees, considered one of the prime honey plants in Europe. The rest of the tree can provide food for plenty of wildlife. Like most members of the pea family black locusts offer the benefit of nitrogen fixing, applicable in both the home garden and land reclamation projects, even being used as a hay crop, mowed down as young shoots to incorporate nitrogen. Its extensive roots can help with erosion control along waterways and slopes. Their juglone tolerance provides another option for spaces where many plants cannot survive. Black locust lumber is some of the very best in the world, though seemingly underappreciated in the American market it is one of the most widely used in Europe. It is extremely hard and strong, comparable to oak or hickory and demonstrates remarkable resistance to rot. Some primary uses are for fence posts, railway ties, and ship building. It also makes wonderful fuel wood.
|Height at maturity||25 metres (82 feet)|
|Spacing||6 metres (20 feet)|
|Sun / shade||Full sun / Partial shade|
|Average fruit weight||n/a|
|Years to bear fruit||n/a|
|Latin name||Robinia pseudoacacia|
|Average diameter of fruit||n/a|
|Also known as||False acacia|