Southern Catalpa

Size, growth and what to expect

Southern catalpa grows fast, and our growth estimator gives it about two and three quarter feet a year while young. It makes a short-trunked tree of 30 to 60 feet, most often 30 to 40, with a broad, irregular crown 20 to 40 feet wide. It lives about 40 to 60 years, and a champion in Mississippi measured 88 feet.

Upright clusters of bell-shaped flowers, each about 1.5 inches across, open in May and June. They are white, with two yellow blotches and dense purple spots in the throat. The leaves grow up to 10 inches long and 6 inches wide. The slender pods, up to 15 inches long, ripen from October into December and hang on through winter, splitting in spring to drop papery, winged seeds. It hosts the catalpa sphinx and tersa sphinx moths, food in turn for birds and bats.

Its native ground is the Gulf coastal plain, from southwest Georgia and the Florida panhandle west through Alabama and Mississippi to Louisiana. After three centuries of planting it grows wild across most of the East.

How to grow Southern Catalpa

Southern catalpa grows in full sun or part shade, but not in full shade. It prefers a moist, fertile loam and takes clay, wet or dry ground and seasonal flooding. Its branches are brittle, and it drops flowers in spring, leaves in fall and pods in winter. Keep it away from walks, patios and septic fields. Plant it 20 feet from a wall and more than 50 feet from overhead wires, and set trees 20 feet apart.

Saplings ship bare-root or potted. Plant them dormant, from leaf fall until bud swell, in a hole wider than the roots and no deeper. Set the root flare at the soil line, put the native soil back in, and keep the mulch clear of the trunk. Collect the pods in late winter, once they are brown and dry, since seed left in the pod over winter sprouts better. The seed needs no treatment. Sow it in spring under an eighth of an inch of soil, and seedlings start coming up in about 12 days.

Water weekly through the first summer. Rabbits girdle young stems, so guard each trunk for its first few winters, though deer seldom browse it. Prune while it is young to build strong limbs on a single leader.

Each flower carries both male and female parts, and bees work the flowers. No study has tested whether a lone tree sets pods. Good crops of pods come every two to three years, beginning at about age 20. Catalpa sphinx caterpillars can strip the leaves once or twice a summer, with no lasting harm to the tree. Verticillium wilt can kill a tree, while leaf spots and powdery mildew are minor. Its winged seed lets it escape from plantings, and outside its home range it spreads into nearby woods.