Tree of the Month: Northern Catalpa
The northern catalpa is a large, stately tree species that stands out in a landscape with its impressive features: a wide, heavy trunk, big leaves that create a full crown, fluffy white flowers, slender bean pods, and its own species of caterpillar to boot. Whether ornamental or functional, these majestic canopy trees contribute significant benefits where they’re planted, including a range of tree-produced ecosystem services, wildlife habitat, and visual interest that draws attention to a specimen throughout the year.
Catalpa Speciosa
The northern catalpa (Catalpa speciosa) is native to the central Mississippi River area where the Ohio River joins it, just northwest of Tennessee. Today, it’s planted widely across the US for its hardy constitution and multiple benefits. This bottomland tree has a distinctive growth form, with a thick trunk and horizontal, twisted branching habits, reaching a mature height of 70 to 80 feet. A catalpa’s trunk and branches have dark, scaly, flaky bark.
The catalpa’s large, irregular crown is made of huge, heart-shaped leaves that resemble elephant ears and are immediately recognizable as catalpa. Catalpa leaves are some of the largest among Nashville’s tree species, measuring up to 10 inches wide and 12 inches long. They’re arranged in an uncommon whorled pattern, which creates a dense foliage that makes these big trees great shade providers.
Following the return of its leaves in the first part of spring, a catalpa tree blooms in May and June. These fragrant, trumpet-shaped flowers are white with yellow and purple spots inside. The blossoms grow in big bunches and attract pollinators, particularly moths and bees (more on this later).
After the flowers have been pollinated, the tree grows very long bean pods. These 10- to 18-inch fruits hang elegantly from the tree throughout the summer and dry into the fall, when the brown beans contrast against yellow autumnal foliage. The leaves fall off, but the pods remain on the tree’s otherwise bare branches over winter, dropping gradually throughout the season.
The Catalpa as a Wildlife Host
As a native species, the catalpa is an important tree for local wildlife. The nectar-producing flowers attract moths, bees, and butterflies that graze across landscapes and help pollinate other specimens. The leaves of a catalpa also produce nectar, which attracts and nourishes pollinators during the summer, in addition to ants and wasps.
A catalpa’s peeling bark and nutrient-rich greenery create microenvironments where small insects like caterpillars, spiders, and beetles can live, which attract woodpeckers, finches, chickadees, and other birds in search of food. The birds avoid a particular species of caterpillar, however, which has a specialized relationship with the catalpa tree.
The catalpa caterpillar (or catalpa worm) is the larval form of the catalpa sphinx moth, an important pollinator of catalpa trees. The caterpillars are yellow-green with black markings. They feed on the leaves of the tree, which contain a chemical that makes them (lightly) toxic to most birds. This allows the caterpillars to grow in large numbers, creating a mutually beneficial relationship between the tree and the insect. While not all catalpa specimens end up with catalpa worms, the trees are sometimes planted to harvest for fishermen who use the caterpillars as bait.
Catalpas in Nashville’s Landscape
As a wetland species, catalpa trees grow well along rivers and lakes and in areas that flood (but which also drain). This results in a preference for loamy, moist soil that drains well, though they can also tolerate clay and slightly alkaline soil. Catalpas are fairly drought-tolerant, making this species a great choice for urban areas. The trees can be rather messy when they drop their large flowers and bean pods, so they may not be suitable for some spaces.
Catalpas thrive in full sun, where they can grow to great heights. Despite the tree’s large size, it’s often planted as a street tree due to its ability to grow in compact spaces. In residential yards, catalpas can grow big and wide to cast dense shade, with cooling effects on the immediate area. As a robust canopy tree, catalpas offer a range of ecosystem services where they’re planted, including soil stabilization, groundwater and stormwater management, and air purification.
The Northern Catalpa’s Lifespan
Catalpas can live over a century, becoming massive, dignified specimens. When cared for properly, a catalpa will produce benefit after benefit, year in and year out, for many decades.
Find the Perfect Tree or Help Plant One!
Check out the Nashville Tree Conservation Corps’ tree sale for your yard’s next planting! If you don’t have space for a new tree, consider donating a tree for us to plant in an open space somewhere in the city, or volunteer with us to lend a hand at a planting or maintenance event.
As a community-based organization, financial donations from Nashville residents and businesses provide us with essential funding for our work around the city. We’re deeply grateful for the generosity Nashvillians continue to show that allows us to fulfill our mission to support Nashville’s canopy ecosystem!
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