1200 Cladrastis kentukeaCommon Names: yellowwood; American yellowwood, Kentucky yellowwood, virgilia, gopherwood Family: Fabaceae (bean Family)
Yellowwood is a medium sized tree that can sometimes reach 60 ft (18 m) in height, but is usually around 40 ft (12 m) tall. Growing in the open, yellowwood develops a broad rounded canopy up to 30 ft (9 m) across on a trunk that often divides into two or three large stems a few feet above the ground. The outermost branches are brittle and often pendulous. The silvery gray trunk bark is smooth, becoming fissured with age, and quite reminiscent of American beech (Fagus grandiflora). First year twigs are bright reddish brown in winter, becoming darker brown by their second year. The compound leaves are odd-pinnate with 7-11 leaflets. The leaves are 8-12 in (20-30 cm) long, and each leaflet is 3-4 in (7-10 cm) long and 1-2 in (3-5 cm) wide, except the terminal leaflet which is shorter and wider than the others. The deciduous foliage turns a clear, bright yellow (sometimes orange) in autumn. In early summer, fragrant white wisteria-like flowers, each about an inch (2.5 cm) long, hang in loose panicles 12-14 in (30-25 cm) long. The flowers are very showy, suspended on slender stalks way out on the ends of the twigs. Flowering is often at its best in alternate years. The thin, flat beanlike pods are 2-4 in (5-10 cm) long, splitting open in winter to release 4-6 little flat seeds.
The cultivar ‘Rosea’ has flowers tinged with pink.
The natural range of Yellowwood, Cladrastis kentukea, is very limited. The species occurs in two disjunct areas: The Ozark Mountains in southern MO and northern AR; and the southern Allegheny Mountains in south-central KY, extreme western NC, eastern TN, and extreme northern AL and GA. Often overhanging mountain streams, yellowwood is partial to limestone outcrops and river valleys. Yellowwood is usually a rare tree where it occurs, but can be abundant along streams that drain to the Ohio River from the western slopes of the Allegheny Mountains. Very popular as an ornamental, yellowwood is widely planted in Europe and in eastern North America as far north as Ontario, and has become naturalized in some areas outside its natural range.
Yellowwood likes a fertile, well drained soil, neutral to acidic. The tree should be sheltered from strong winds since the branches and twigs are brittle. The trunk of yellowwood has a tendency to divide into two or more low stems that then become susceptible to breaking apart. To avoid this, the tree should be kept pruned to a central leader. Don’t prune in late winter or spring since the tree bleeds sap profusely at that time of year and this could weaken it. It may take as many as 8-10 years for a newly planted yellowwood to bloom the first time, and flowering usually is heaviest in alternate years. But, it’s well worth the waiting! Light: Yellowwood does best in full sun or mostly sun. It likes more shade in areas with hot summers. Moisture: Yellowwood expects ordinary soil moisture but can tolerate dry soil. Hardiness: USDA Zones 4 - 9. American Yellowwood tolerates winter low temperatures below -22°F (-30°C), even though it doesn’t get that cold in its natural range. Propagation: Propagate yellowwood from root cuttings in winter or sow seed after scarifying and stratifying at 40°F (5°C) for three months.
Although rare in nature, yellowwood is well known in cultivation, and a good, low maintenance choice for landscaping, even in urban settings. Yellowwood is tolerant of alkaline as well as acidic soils. Position in small groups in larger settings, and as single specimens in smaller lawns. This is a graceful, full-canopied tree that makes an excellent specimen in all seasons. In spring yellowwood is virtually covered with intensely fragrant white flowers that remind one of wisteria (Wisteria sinensis) or black locust (Robinia pseudoacacia). In summer it is a fine shade tree that casts a very heavy shadow with its dense canopy of brilliant green compound leaves. Bright yellow to orange foliage signals the autumn season. The smooth gray bark and red-brown twigs maintain interest in winter. Because yellowwood is full canopied with low branches, you don’t have to back off to appreciate the flowers.
The wood is fine textured, hard and heavy. It is sometimes used for gun stocks and art carvings. The heartwood is a clear, bright yellow and has been used to make a yellow dye. The flowers are very popular with bees and other insects.
American yellowwood is listed as Endangered in Illinois and Threatened in Indiana. There are three other species of Cladrastis, one in Japan and two in western China. The genus name is from the Greek, meaning fragile branch.
Steve Christman 10/19/13