Catalpas are among the few truly deciduous trees that can compete in flower and leaf with subtropical species. They bloom in late spring and summer, bearing large, upright clusters of trumpet-shaped, 2-in.-wide flowers in pure white, striped and marked with yellow and soft brown; flowers are held above large, bold, heart-shaped leaves. Long, bean-shaped seed capsules, sometimes called Indian beans, follow the blossoms.
Unusually well adapted to extremes of heat and cold; take any type of soil. Where winds are strong, plant in lee of taller trees or buildings to protect leaves from damage. Some gardeners object to litter of fallen flowers in summer and seed capsules in autumn. Plants need shaping while young; they seldom develop a well-established dominant shoot on their own. Shorten side branches as tree grows. When branching begins at desired height, remove lower branches.
For the tree sometimes called desert catalpa, see Chilopsis linearis. Another tree sometimes mistakenly called catalpa is the very similar Paulownia tomentosa (empress tree), with lavender flowers. Paulownia shows flower buds in winter; catalpa does not.
C. bignonioides. COMMON CATALPA, INDIAN BEAN. Native to southeastern U.S. Grows to 3050 ft. according to climate or soil, with somewhat smaller spread. Leaves are 58 in. long, often in whorls, and give off an odd odor when crushed. Subject to chlorosis (yellow leaves with green veins) in alkaline soil. Yellow leaves of 'Aurea' are showiest in the Upper South. 'Purpurea' has dark purple new growth that later turns green. 'Nana', or umbrella catalpa (usually sold as C. bungei.), is a dense globe form usually grafted high on C. bignonioides; it grows about 6 ft. high, 5 ft. wide, and never blooms.
C. xerubescens 'Purpurea'. Selection of a hybrid between C. bignonioides and C. ovata; resembles C. bignonioides. Leaves (to 1016 in. long) and branchlets are deep blackish purple when young, maturing to purplish green in summer.
C. speciosa. NORTHERN CATALPA. Native to central and southern Midwest. Round headed; 4070 ft. tall, 2040 ft. wide. Leaves 612 in. long. Fewer flowers per cluster than for C. bignonioides. Early training and pruning will give tall trunk and umbrella-shaped crown.