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Psorodendron spp.

indigo bush

Fabaceae Southwestern North America

Attracts Pollinators Attracts Butterflies Deer Resistant Drought Tolerant Fragrant (moderate)Container Friendly

Native to North America

SunFull Sun

WaterVery Low · drought-tolerant

HardinessZones 8–11

Overview

Psorodendron spp. is a genus of spiny, drought-deciduous desert shrubs and small trees in the pea family (Fabaceae), native to the arid southwestern United States and northern Mexico. The genus was segregated from Psorothamnus spp. and includes the smoke tree P. spinosum and several indigo bushes. Plants are intricately branched and grayish, often spine-tipped, growing 3-25 feet (0.9-7.6 m) tall depending on species, with the smoke tree reaching the upper end. The small pinnate leaves are quickly shed in drought, so for much of the year the plant appears as a haze of gray, glandular, scented twigs. In late spring and summer the branches carry short spikes of small pea-shaped flowers in deep indigo, violet, or purple-blue, followed by tiny pods. Gland dots on the foliage release a resinous scent when crushed. The genus is adapted to extreme heat, intense sun, and sandy desert washes, and it tolerates long drought but not wet or poorly drained soil. Frost tolerance is limited.

Native Range

Psorodendron spp. is native to the deserts of the southwestern United States, including California, Arizona, and Nevada, and adjacent northern Mexico. Species grow in sandy washes, rocky slopes, and creosote scrub of the Sonoran, Mojave, and Chihuahuan deserts.

Suggested Uses

Grown in desert, xeric, and low-water gardens as a specimen or informal screen, and in native plantings across the arid Southwest. The smoke tree is used along dry washes and in naturalistic desert landscapes. The deep blue bloom and gray structure suit cactus and succulent gardens.

How to Identify

Recognize Psorodendron spp. by its intricately branched, gray, often spine-tipped twigs and its small, gland-dotted pinnate leaves that drop in dry spells. The deep indigo to violet pea flowers appear in short spikes, followed by small one- to few-seeded pods. Crushed foliage and twigs give off a resinous scent.

Appearance

Size & Dimensions

Height3' - 25'

Width/Spread3' - 20'

Reaches mature size in approximately 5 years

Colors

Flower Colors

Foliage Colors

Fall Foliage Colors

Bloom Information

Bloom Period

~4 weeks

Spring Summer

Flowering occurs mainly in late spring and early summer, roughly April to June, with the timing tied to available moisture. The deep blue-purple flowers open over a few weeks. In wetter years a lighter second flush can follow summer rains.

Detailed Descriptions

Flower Description

indigo to violet-purple

Foliage Description

gray-green

Growing Conditions

Sun Requirements

SunFull Sun

Requires 8-12 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

Soil Requirements

pH Range6.5 - 8.5(Alkaline)

357912

Soil Types

sand rocky

Drainagewell drained

Water & Climate

Water Needs

Very Low

Frost Tolerance

tender

Time to Maturity

3-5 years

Drought Tolerance

Drought tolerant when established

Care & Maintenance

Care Guide

Grow Psorodendron spp. in full sun in sharply drained sandy, gravelly, or rocky soil typical of desert gardens. The genus needs heat and tolerates intense sun, reflected heat, and prolonged drought once established. Water deeply but infrequently while young, then little to none once established, as wet or heavy soil causes root rot. Rich soil and heavy feeding produce weak, leggy growth. Plants are frost-sensitive and suited to low-desert and warm Mediterranean climates, and the sharp spines on many species are a consideration when positioning plants near paths.

Pruning

Psorodendron spp. needs little pruning and naturally forms an intricate, twiggy structure. Dead or crossing branches can be removed in late winter before growth resumes. Hard cutting is kept to a minimum, as old desert wood is slow to regenerate.

Pruning Schedule

winter