The American yellowwood, Cladrastis kentukea, is one of the rarest native trees of North America.  Its occurrence in the wild is primarily on isolated limestone-rich calcareous cliffs and bluffs from western Virginia and North Carolina westward to the Ozarks.  Despite its rather particular natural habit, this small, highly-adaptable tree is quite happy in wide range of soil and pH types, its main requirements being ample sunlight and good drainage.   It is hardy to USDA Zone 4 (-30 °C / -25 °F).  Cladrastis is a small genus in the Fabaceæ, or legume (pea) family with three sister species found in Asia.  It is very closely related to Styphnolobium (pagodatree).

Yellowwood is a moderately fast-growing tree, suitable for a variety of uses.   Its smaller size makes it very adaptable to the residential landscape.  At maturity, it typically grows to 10–15 m (35–50 ft) in height with a broadly-rounded crown.  Like most members of the pea family, the leaves are pinnately compound, 20-30 cm (8-12”) in length with 5-9 alternate oval leaflets; dark green above with paler undersides.  Typical fall color is shades of gold, yellow, and orange.  The twigs are a light yellow-green when young, gradually turning reddish-brown then dark brown with age.   The thin mature bark is brownish-grey and somewhat reminiscent of that of Fagus (beech).

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Cladrastis kentukea blooms in late spring, typically mid-May to early June in the Mid-Atlantic.  The flowers are Wisteria-like, in pendulous racemes 15-40 cm (6-16”) long; the individual blossoms are white with a pale-yellow blotch and are lightly fragrant.  They are highly attractive to both bees and butterflies.  Flowering density varies from year to year with more numerous flowers every second or third year.   The flowers are followed by the typical legume seedpod, green turning brown, 5–8 cm (2-3”) long, and containing up to six seeds.

As noted above, yellowwood typically develops a broadly rounded crown in the landscape.  It does tend to branch low to the ground and can develop poor crotches, so it benefits from judicious pruning maintenance.   Unlike many trees, Cladrastis kentukea should be pruned in summer as spring pruning can lead to excessive ‘bleeding’ during sap rise.   Besides giving a greater strength to the tree, pruning also helps accentuate the fine zigzag structure of the branching, which is another attractive aspect, especially in winter.  Pruning also helps protect yellowwood from winter damage; in fact the genus name Cladrastis literally means “brittle branch”, from Greek klado, a branch, and thraustos, fragile.  Caution should also be used when trimming around the tree as its bark is relatively thin. Outside of this, yellowwood is virtually pest-free and is highly drought-tolerant once established.

The common name yellowwood derives from the tree’s bright yellow heartwood and is occasionally used for small furniture, gunstocks and decorative items.  The bark of the tree roots was used by native Americans and early European settlers to make a stable bright-yellow dye.

In summary, Cladrastis kentukea is a unique small tree ideally suited for year-round interest in the suburban residential yard and is a great native alternative to other common ornamentals such as Prunus and Lagerstrœmia.  It is available from White House Natives in 1½” up to 3” calipers.

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