The royal empress tree (Paulownia tomentosa) is one of the fastest-growing trees of temperate climates. Hardy in U.S. Department of Agriculture plant hardiness zones 5b through 9b, it is truly regal with its heart-shaped leaves and unusually fast growth rate. Royal empress trees add interest to the landscape throughout the growing season with their flowers, foliage and seed capsules.
Impressive Spring Flowering
The growing season for the royal empress tree starts in early spring when the foot-long flower clusters emerge on its bare branches. The individual flowers are about 2 inches long, purple, tubular in shape and fill the air with a sweet, vanilla-like fragrance. The flower clusters themselves decorate the entire periphery of the tree, growing only from the tips of the previous season's growth. Empress flowers have an erect growth habit, which differentiates them from related species with similar growth habits, but drooping flower clusters.
Gargantuan Summer Growth
Even more than the royal empress tree is known for its flowers, it is celebrated for its rapid growth habit. It is capable of growing 10 feet or more in a year and matures into a medium-sized shade tree within three to five years. It provides dense shade with with leaves up to 12 inches across that are covered in a velvety fuzz. The branch structure of the royal empress tree is particularly attractive with its upright, symmetrical growth habit.
Fall Seed Dispersal
The royal empress tree is not known for it fall color -- within a week of the first frost in fall, the leaves turn from green to brown and fall off the tree. However, it is a prolific seed producer. The inch-long seed capsules develop over summer, ripen in the fall and decorate the tree throughout the winter. Each capsule contains upwards of 2,000 tiny seeds and there may be thousands of capsules on a mature tree. These germinate readily, making this native of China highly invasive in some locations, particularly in the eastern United States.
Care Through the Seasons
The royal empress tree is generally very tough and adaptable, requiring little care. It is surprisingly drought-tolerant for a tree with such large leaf surfaces, but irrigation will help it to sustain its lush and rampant growth. Empress trees are adapted to most soil types and fertilizer is generally not used because the tree grows like a weed without it. The primary maintenance task with the empress tree is to clean up after it -- the prolific leaf litter, flower petals and seed capsules make raking a constant chore around the tree in fall, winter and spring.