Phellodendron spp.

cork tree

HardinessZones 4–7

Overview

Phellodendron spp. is a genus of about 10 deciduous trees in the citrus family (Rutaceae), native to East Asia and known as cork trees for the thick, ridged, corky bark of mature trunks. Plants grow 30-45 ft (9-14 m) tall with a broad, spreading, open crown often wider than high. The aromatic pinnately compound leaves, 10-15 in (25-38 cm) long, have 5-13 leaflets that release a citrus or turpentine scent when crushed and turn clear yellow in autumn. Trees are dioecious, with separate male and female plants; small yellow-green flowers in early summer give way, on female trees, to clusters of pea-sized black drupes that smell sharply of citrus when bruised. The fruit is eaten by birds, and seedlings of P. amurense have escaped cultivation and are classed as invasive in parts of the northeastern United States. Male, fruitless selections are planted to prevent this spread.

Native Range

Phellodendron spp. is native to East Asia, including northeastern China, the Russian Far East, Korea, and Japan, where species grow in mixed forests, valley woodlands, and along streams. P. amurense, the Amur cork tree, is the species most often planted and the most prone to naturalizing.

Suggested Uses

Phellodendron spp. is grown as a shade, lawn, street, and park tree where its corky bark, fall color, and broad canopy suit large open spaces. Trees are spaced 30-40 ft (9-12 m) apart to allow the wide crown to spread. Male, fruitless clones are used to keep self-seeding in check.

How to Identify

Identify Phellodendron spp. by its thick, deeply furrowed, corky gray bark and aromatic pinnate leaves whose crushed leaflets smell of citrus or turpentine. The broad, low-branched, spreading crown and, on female trees, clusters of small black drupes are further marks. Cutting a twig reveals bright yellow inner bark, a feature shared with other Rutaceae.

Appearance

Size & Dimensions

Height30' - 45'

Width/Spread30' - 45'

Colors

Flower Colors

Foliage Colors

Fall Foliage Colors

Bloom Information

Bloom Period

~2 weeks

Spring Summer

Flowering occurs in late spring to early summer, generally May to June, in small branched clusters of yellow-green flowers at the shoot tips. Male and female flowers grow on separate trees, so only female trees set fruit. Black drupes ripen in autumn and persist after the leaves fall.

Detailed Descriptions

Foliage Description

Dark green, clear yellow in autumn

Growing Conditions

Sun Requirements

SunFull Sun

Requires 6-10 hours of direct sunlight daily

• Full Sun: 6+ hours of direct sunlight

• Partial Shade: 3-6 hours of direct sunlight

• Full Shade: Less than 3 hours of direct sunlight

Soil Requirements

pH Range5.5 - 7.5(Neutral)

357912

Soil Types

loam clay sand

Drainagewell drained

Water & Climate

Water Needs

Low

Frost Tolerance

hardy

Time to Maturity

15-20 years

Drought Tolerance

Drought tolerant when established

Care & Maintenance

Care Guide

Phellodendron spp. grows in full sun in deep, well-drained loam across a wide pH of 5.5-7.5, and tolerates heat, drought, urban soils, and air pollution once established. The genus is hardy through USDA zones 4-7 and adapts to a range of conditions, which is part of why P. amurense can naturalize. Trees develop a wide, low crown and need ample lateral room rather than a confined site. Few pests or diseases trouble them. Where seeding into wild land is a concern, male clones are chosen so no fruit forms. Little care beyond early structural pruning is needed.

Pruning

Phellodendron spp. needs formative pruning when young to set a strong framework and raise the low branches for clearance. Dead, crossing, or rubbing limbs are removed in winter. Mature trees keep their broad form with little further cutting.