Golden Rain Tree, Koelreuteria paniculata

For zone 5b.

Koelreuteria paniculata or Soap Tree is a tree in the Sapindaceae family native to China and Korea. The mature tree measures 7 to 10 m in height and 4 m in spread. It has a relatively slow growth. It has become an ornamental tree in temperate regions for its aesthetic appearance. It is a deciduous tree that can reach a height of 12 m at maturity. Its shape is widely spread, its bark brown to pale brown, cracked. Its leaves are pinnate or partly bipinnate, and are about forty centimeters long. They consist of lobed or serrated leaflets, or divided into leaflets about 10 cm long. In the fall, its green foliage turns golden, hence its name in English: Goldenrain tree.

The flowers, with four yellow petals, form at the end of the branches in conical panicles 20 to 40 cm long. These panicles form in the second part of summer, and give rise to lantern-shaped capsules, 3 to 6 cm long and 2 to 4 cm wide. These initially pale green become brown-brown when ripe. Each fruit lobe contains a dark brown, spherical seed with a diameter of 4 to 7 mm. The fruits persist until the following spring. Despite its name, it is not its fruits that are used to make soap, but those of a tree in the same family, the Sapindus mukorossi. It needs full sun, which also favors its most beautiful flowering, and cannot tolerate shade or partial shade. Appreciating dry soils, it cannot tolerate waterlogged soils, temporarily or permanently.