Psorodendron spinosum
Smoketree
Overview
Psorodendron spinosum is a spiny, gray-barked shrub or small tree of the Sonoran Desert, growing 6–25 feet (1.8–7.5 m) tall with a broad, intricately branched, often leaning crown. The slender gray twigs are densely covered in short gray hairs and tipped with sharp spines, and the small simple leaves 0.2–0.5 inch (5–12 mm) long drop early, leaving the plant nearly leafless and giving it a smoky gray cast from a distance. Fragrant indigo to violet-blue pea-shaped flowers about 0.5 inch (12 mm) long appear in short clusters from May to July. Small one- to two-seeded pods follow. P. spinosum grows almost exclusively along sandy and gravelly desert washes from southeastern California and Arizona south into Baja California and Sonora, where periodic flooding scours and scarifies its hard-coated seeds. It tolerates extreme heat and drought but requires the deep, intermittently flooded soils of desert washes and is sensitive to hard frost.
Native Range
Psorodendron spinosum is native to the Sonoran Desert of southeastern California, southwestern Arizona, and northwestern Mexico, including Baja California and Sonora. It grows along sandy and gravelly desert washes and arroyos.Suggested Uses
Used as a specimen or screen in desert gardens and in revegetation of arid washes. Spaced 12–20 feet (3.7–6 m) apart, it suits large xeric landscapes and shelters desert wildlife.How to Identify
Appearance
Size & Dimensions
Height6' - 25'
Width/Spread6' - 20'
Reaches mature size in approximately 15 years
Bloom Information
Flowering occurs from May to July. The fragrant indigo to violet-blue pea-shaped flowers, about 0.5 inch (12 mm) long, open in short clusters along the twigs and draw bees. Small pods of one or two seeds follow.
Detailed Descriptions
Flower Description
indigo to violet-blueFoliage Description
gray-greenGrowing Conditions
Sun Requirements
Requires 6-12 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
Care & Maintenance
Care Guide
Grow P. spinosum in full sun in deep, sharply drained sandy soil. It tolerates extreme desert heat, intense sun, and long drought once established but requires occasional deep watering that mimics the periodic flooding of its native washes. Soil pH from 7.0 to 8.5, including alkaline soils, is suitable. Seeds germinate only after the hard coat is scarified, so growth from seed is slow and erratic. The plant is sensitive to hard frost and grows slowly. Established trees need little water beyond infrequent deep soakings.Pruning
Prune in late spring after flowering to remove dead or crossing branches and to lift the crown. The spines make pruning slow work. Mature plants need little shaping and are damaged by heavy cutting in the hottest months.Pruning Schedule
J
F
M
A
M
J
J
A
S
O
N
D
late spring