Paulownia tomentosa (Thunb.) Steud.

Paulownia imperialis is a deciduous tree attaining a height of 12-16 m, occasionally over 20 m. The crown is open and domed, containing relatively few branches that often begin quite near the ground. Bark is smooth and delicately streaked, reddish-grey in colour on young trees and of a distinct grey hue in older trees. Opposite leaves heart shaped with a basal notch, a light colouring of downy hairs on their top side and densely pubescent underside; entire, measuring up to 35 x 25 cm, with a stalk 10-15 cm long. Flowers pale-violet to blue-purple, slenderly campanulate, up to 6 cm long, arranged on panicles 20-30 cm long. Fruits grow on stalks, ovoid in shape, whitish-green in colour and sticky to the touch. About 3 x 1.8 cm in size; 2-10 grow on each panicle, each opening in 2 valves releasing winged seeds 3-5 mm. P. imperialis was named in honour of Anna Pavlovna (1795-1865), daughter of Czar Paul I of Russia and wife of Prince (later King) Willem of the Netherlands.

P. imperialis bears fruit regularly from age 15 onwards. In eastern and southern USA, the flowers appear in April and May before the leaves emerge. The fruits turn brown in the autumn, when they mature and persist on the tree throughout the winter.

Thrives best in moderately acid to alkaline soils (pH 5-8), but is relatively undemanding to nutrient availability. It prefers well-drained, sandy to loamy soils.

P. imperialis prefers a warm temperate to warm climate. Studies in China have shown that it flourishes best at daytime temperatures of 24-30 deg. C; its height growth ceases at daytime temperatures of 15-20 deg. C. Sufficient ventilation of the soil is vital; on poorly draining sites, after 3-5 days of uninterrupted rainfall P. imperialis casts off its leaves and dies. It is easily damaged by wind. It is an intolerant pioneer species, colonizing cleared disturbed areas such as roadsides, mined areas, sanitary landfills, abandoned agricultural soils, and deep, moist but well-drained alluvial soils along waterways.

The genus Paulownia probably originated in subtropical China, around Szechwan and Hupeh. Today trees are found in large parts of China, Korea, Taiwan and Japan. The tree is cultivated extensively in Japan, having been introduced there at an early date. It is the celebrated t’ung tree of Chinese classics, valued since ancient times as an ornamental and for its high-quality timber. The first P. imperialis in a European garden was introduced by Siebold to France through Jardin du Roi, which later became the Jardin des Plantes. His specimen left Japan in January 1829 and arrived in Holland in 1830. The tree was introduced to eastern United States of America during the late 1800s, where it frequently escaped from cultivation and became naturalized in the woods.

Seeds germinate within 20-30 days after sowing. The tree can be readily propagated by vegetative means using root cuttings and root suckers. Underdeveloped plants are retained in the nursery, pruned back after they shed their leaves and transplanted to the field a year later.

P. imperialis grows extremely quickly. Stock grown from seeds attains a height of 3-4 m by the end of the 1st year, with a diameter of 3-5 cm at ground level. Root cuttings can be as high as 4-5 m, occasionally 8 m, after 1 year. Field planting is recommended of young plants 4-5 m tall with a diameter 4-6 cm just below the crown. Under favourable, conditions a large tree may produce as many as 20 million seeds in a year. Paulownia is a pioneer species requiring direct sunlight. For this reason, young trees should be kept free from weed competition. A spacing that results in 500 trees/ha (about 2.75 x 2.75 m) is recommended to produce high-quality trees of good form.

Two species of fungi, Ascochyta paulowniae and Phyllosticta paulowniae, cause leaf spots during very rainy seasons.

Orthodox storage behaviour; 85-93% germination after 3 years hermetic storage at 4 deg. C. There are between 4 and 6 million seeds/kg, or about 6200 seeds/g.

Shade or shelter: P. imperialis is suitable for planting in shelterbelts. Reclamation: Its tenacity in rooting and its tolerance of rocky, disturbed and relatively infertile soils boosts its potential use in reclamation of surface mines, for example in Kentucky, USA. Ornamental: As a park and ornamental tree, it is widespread in temperate zones including Germany (in the wine-growing areas), southern Europe and USA. Intercropping: Particularly well suited for intercropping with wheat, cotton and maize at spacings of 5 x 20 m and 5 x 50 m; the resulting yields of wheat are 16% higher, those of cotton 7% higher, and those of maize more than 11% higher than those from plots without P. imperialis.

Fibre: P. imperialis yields an excellent chemical pulp of a quality far superior to that of other fast-growing, broadleaved tree species. Apiculture: In Kentucky this valuable tree provides pollen and nectar for bees (Hill and Webster,1995). Timber: The wood has a uniformly coloured, light-brown heartwood, and a narrow, light-grey sapwood. P. imperialis is the lightest wood grown in China (specific gravity 0.3 g/m³). It is odourless, has good physical properties and is easy to season but is only moderately durable. Because of its above-average acoustic properties, it is used in China for making traditional musical instruments. Its other applications include models and glider construction, sculptures, small utensils and domestic articles. In Japan, it is used for making matches, wooden shoes and crates. Plantation-grown wood from Brazil is often utilized for simple furniture. The popularity of P. imperialis among the Chinese has inaugurated the convenient custom of planting a sapling at the birth of a daughter. By the time the girl is old enough to get married the tree is big enough to be used for the construction of her wardrobes, which are important articles in her dowry. Lipids: Oil for varnishing is obtained from the seed. Medicine: The leaves, flowers, fruits and roots are used in China for making medical decoctions. An aqueous solution prepared from the leaves and capsules is prescribed for daily application over the head to promote a healthy growth of hair, and another for turning grey hair black. An aqueous solution prepared from the leaves and wood is prescribed for swollen feet. A tincture prepared from heating the inner bark with water and whiskey is administered internally to patients having high fever and delirium. The leaves steamed in vinegar or the bark fried in vinegar are prescribed as a dressing for bruises. An aqueous concoction made from the flowers and other Chinese plants is administered internally for the cure of ailments of the liver or bile that cause dizziness.