Cladrastis kentukea: American Yellowwood

Introduction

Yellowwood is so named because the freshly cut heartwood is a muted to brilliant yellow color, and the wood is known to yield a yellow dye. This seldom-used, native, deciduous tree makes a very striking specimen or shade tree, reaches 30 to 50 feet, rarely 75 feet in height, with a broad, rounded canopy and a vase-shaped, moderately dense silhouette. Smooth, grey to brown bark; bright green, pinnately compound, 8- to 12-inch-long leaflets; and a strikingly beautiful display of white, fragrant blossoms make yellowwood a wonderful choice for multiple landscape uses.

General Information

Scientific name: Cladrastis kentukea

Pronunciation: kluh-DRASS-tiss ken-TUCK-ee-uh

Common name(s): American yellowwood, virgilia

Family: Leguminosae

USDA hardiness zones: 4A through 8B (Fig. 2)

Origin: native to North America

Invasive potential: little invasive potential

Uses: specimen; shade; street without sidewalk; highway median

Availability: somewhat available, may have to go out of the region to find the tree

Description

Height: 30 to 50 feet

Spread: 40 to 50 feet

Crown uniformity: irregular

Crown shape: round, vase

Crown density: moderate

Growth rate: moderate

Texture: medium

Foliage

Leaf arrangement: alternate (Fig. 3)

Leaf type: odd-pinnately compound

Leaf margin: entire

Leaf shape: elliptic (oval), ovate

Leaf venation: brachidodrome, pinnate

Leaf type and persistence: deciduous

Leaf blade length: 2 to 4 inches

Leaf color: green

Fall color: copper, yellow

Fall characteristic: not showy

Flower

Flower color: white/cream/gray

Flower characteristics: very showy

Fruit

Fruit shape: elongated

Fruit length: 1 to 3 inches, 3 to 6 inches

Fruit covering: dry or hard

Fruit color: white/gray

Fruit characteristics: does not attract wildlife; showy; fruit/leaves not a litter problem

Trunk and Branches

Trunk/bark/branches: branches droop; showy; typically one trunk; thorns

Pruning requirement: needed for strong structure

Breakage: susceptible to breakage

Current year twig color: brown

Current year twig thickness: thin

Wood specific gravity: unknown

Culture

Light requirement: full sun, partial sun, or partial shade

Soil tolerances: clay; sand; loam; alkaline; acidic; occasionally wet; well-drained

Drought tolerance: moderate

Aerosol salt tolerance: unknown

Other

Roots: can form large surface roots

Winter interest: yes

Outstanding tree: no

Ozone sensitivity: unknown

Verticillium wilt susceptibility: susceptible

Pest resistance: free of serious pests and diseases

Use and Management

The 1-inch-wide, fragrant flowers appear in dense, showy, pendulous, terminal panicles, 12 to 14 inches long, in early summer, and are set off nicely against the lush foliage. Flowers are visited by a large number of bees. Trees may not flower until they are 10 years old and then seem to give outstanding displays only in cycles of every 2 to 5 years, but the gorgeous display is well worth the wait. The flowers are followed by showy, 3- to 4-inch-long, whitish-grey pods that persist through the winter.

Unpruned trees fall apart in 30 to 40 years. Yellowwood should be pruned when young to develop branches having a wide angle with the trunk and a U-shaped crotch. These should be pruned back so that they are not allowed to grow larger than half the diameter of the trunk. Develop 7 to 10 major lateral limbs spaced along the trunk, not clustered together. Good luck! This will help them develop strong attachments to the trunk and provide for a longer-lived tree than one that is not pruned in this way. Weakly attached branches with embedded bark are susceptible to breakage and may be a problem as the tree grows older. Any pruning should be done in summertime because excess bleeding may occur if done in the winter or spring. It could be used as street tree if properly pruned to avoid weak crotches. It is often planted as a specimen or shade tree for smaller properties due to its flowers and medium size.

Yellowwood grows slowly in full sun on moist, well-drained soils, but growth may be more rapid if provided with some shade in the southern part of its range and in the plains states. It grows slowly on poor soil but looks fine, responding to better soil with moderate growth. It tolerates alkaline (it is native to dry limestone outcroppings, as well as along stream banks) or acidic soil and urban conditions. It performs well with only occasional irrigation once established, even in poor, compacted soils. It adapts to wet soils by growing a shallow root system. There are several very large, coarsely branched roots dominating the root system, which makes care following transplanting very crucial. But planting from containers is no problem.

The cultivar 'Rosea' has pinkish flowers.

Propagation is by seed or cuttings.

Pests and Diseases

No pests or diseases are of major concern. Verticillium wilt may occasionally be a problem.