Cladrastis, also called yellowwood, is a genus consisting of seven species of deciduous trees within the Fabaceae family. One species, C. Lutea, is native to the southeastern region of North America, while two species, C. platycarpa and C. sikokiana, are native to Japan. The species C. parvifolia, C. sinensis, and C. wilsonii are native to China. All trees within this genus grow approximately 1 foot (0.3) annually until attaining their maximum height of 40 to 50 feet (12 to 15 meters).
The fruit of these trees is a pod that contains one to six seeds and is 1.2 to 3.2 inches (3 to 8 cm) long. A yellow dye can be extracted from the inactive central wood of Cladrastis species. Wood obtained from the trees is close-grained, durable, and very hard.
Trees of the Cladrastis genus have feather-like leaves and branches that spread out to form a round canopy. These light green, oval-shaped leaves become yellow during autumn, while the bark is gray and smooth. Their flowers are typically white or pink in color and are said to have a light scent similar to that of vanilla.
American yellowwoods are capable of adapting to most growing conditions and climates. One variety of this flowering plant, commonly named Rosea, produces pink flowers. Chinese species of Cladrastis have pink-tinged flowers, and their leaves are more textured and narrow than American yellowwoods. The Japanese species produce flowers tinged with yellow.
Flowers are produced either in the beginning of summer or the end of spring. Young trees produce flowers sparsely and, in some instances, not at all. Fully grown Cladrastis trees produce more flowers, but only every two to three years. Some people believe these trees can regularly produce flowers when strained by drought. Cascades of flowers that reach up to 15 inches (38 cm) hang from the branches and resemble wisteria.
The seeds of Cladrastis trees may be sown when the tree has ripened. They should be soaked in warm water for 24 hours and sown during winter, preferably in a greenhouse. Seed germination typically occurs within one to three months at around 50 ºF (-10 ºC).
Once the seedlings are big enough to be handled, they can be put into separate pots and grown in a cold frame during winter. The seedlings can be planted outdoors around early summer or late spring after the frost has subsided. They have an abundance of watery sap that may bleed if they are pruned during spring or winter. Cladrastis saplings flourish in loamy, well-drained soil with plenty of sunlight, but they can also tolerate acidic and alkaline soils. The branches of these trees are generally brittle and may be snapped by strong winds, so some sort of shelter is recommended.