Toxicodendron diversilobum
Common Name: western poison oak 
Type: Deciduous shrub
Family: Anacardiaceae
Native Range: Northern Mexico, southwestern United States
Zone: 5 to 9
Height: 3.00 to 10.00 feet
Spread: 2.00 to 7.00 feet
Bloom Time: April to June
Bloom Description: White
Sun: Full sun
Water: Medium
Maintenance: High
Flower: Showy
Leaf: Good Fall
Fruit: Showy
Tolerate: Drought

Culture

Best grown in light, moist, sandy to medium, well-drained loams in full sun. Somewhat wide tolerance for different types of soils as long as drainage is good. Tolerates some part shade, but full shade should be avoided. Plants are dioecious (separate male and female plants). Poison oak is not an ornamental plant. If found in the landscape in its native range, it is usually removed immediately by mechanical (carefully dig up) or chemical (herbicides such as glyphosate) means.

Noteworthy Characteristics

Toxicodendron diversilobum (synonymous with Rhus diversiloba), is commonly called poison oak. It is noted for causing significant and long-lasting skin irritations (allergic dermatitis) in most humans who come into contact with the plant. It is native from British Columbia south to Baja California, from sea level to about 5000 feet in elevation, primarily in areas west of the Cascades and Sierras. It is typically found along the coast in scrubby areas or open woodland areas and further inland in valleys, foothill thickets, grassy hillsides, coniferous forests and along streams. This is a deciduous shrub (to 3-10’ tall) or climbing vine (to 50’ tall) that features trifoliate leaves with ovate to obovate oak-like leaflets. Leaves emerge with burgundy tinting in spring, mature to glossy green in summer and turn sometimes attractive shades of gold and red in fall. White flowers bloom in spring. Fertilized flowers on female plants give way to white to green-white spherical fruits in summer. This western form is sometimes commonly called Pacific poison oak.

Genus name means poison tree.

Specific epithet means diversely lobed.

Problems

Do not touch any part of poison oak. It is considered to be a hazardous plant. Wear gloves and other protective clothing when around this plant. Any unprotected contact with poison oak (by direct touching or by pets/animals or by inhaling smoke from burning plant material) can cause significant and long-lasting skin irritations (allergic dermatitis) in reaction to a toxic plant oil known as urushiol.

Garden Uses

This plant is not grown ornamentally and is not recommended for planting in gardens or landscapes.