I can’t help but smile as I wander around our farm or drive down the roads at this time of year. So many plants, especially trees, are busting into bloom. For the past week or so, the one that has brought the biggest smile to my face is black locust (Robinia pseudoacacia).
Black locusts are the tall trees that currently have the cascades of white flowers. From a distance, I think they look like the outside limbs are piled with snow – except that it’s 70-80 degrees outside. You tend to find them growing along the edges of woods and in disturbed areas like road right-of-ways.
Black locusts are native to the Appalachian region and parts of the Ozarks, but have been widely planted across the U.S. and in parts of Canada. They have even been exported to other parts of the world where they are often planted as ornamental trees. Black locusts grow very quickly but are considered relatively short-lived because they rarely reach 100 years old. The wood is very strong and was commonly used as fence posts which is one reason why it was planted so frequently in historic times.
The flowers form in clusters of medium-sized white flowers that are shaped like the flower of a pea. There is a good reason for that – it is in the same family as the pea. Like peas and beans, black locusts are nitrogen fixers and have bacteria associated with their roots that improve the nitrogen levels in the surrounding soil.
The white flowers of the black locust have a sweet smell and produce abundant amounts of nectar and pollen. In Kentucky, they primarily bloom in late April and early May. The exact timing of the bloom depends partially on where you are located in the state and what the weather has been like. Warmer weather tends to cause the bloom to start earlier, where as, a cooler spring may delay the bloom slightly.
Black locust flowers are a favorite spring flower for pollinators, especially honey bees and many species of native bees. The black locust trees on our farm are literally buzzing with activity. Beekeepers are especially fond of black locust trees because black locusts are often one of the primary sources of honey that can be harvested in the spring.
It’s important to note that the black locust (Robinia pseudoacacia) is not the same tree as the honey locust (Gleditisia triacanthos). Despite its name, the honey locust doesn’t result in as much honey production as the black locust. I’ll write another blog post later about the honey locust, but for now just remember that it is a completely different tree from the black locust.
In addition to honey bees and native bees, hummingbirds and many species of butterflies and moths also visit black locust flowers. Black locust trees are also important host plants for many caterpillar species including that of the silver-spotted skipper and the clouded sulphur. The caterpillars don’t pollinate the flowers, but instead eat the leaves before undergoing metamorphosis into a butterfly or moth.
Black locusts are also valuable to many other wildlife species. Many species of songbirds make their homes in the branches or eat the caterpillars and other insects that feed upon the leaves. White-tailed deer, rabbits, squirrels, and some of our larger birds like quail and turkey have all been known to eat black locust foliage or seed pods. However, care should be taken with livestock around black locust because many sources report that it can be toxic to livestock.
While they may not be as well-known as some other types of trees such as oaks and maples, black locusts are a valuable part of our forest ecosystems. They provide food and homes for pollinators and other wildlife species throughout the year. This year, we are having a strong locust bloom which makes it easy to spot this beautiful tree and to observe the many pollinators that use its flowers.