Psorothamnus spinosus (Smoke Tree)
Foliage: Semi-Evergreen
Mature Height: 12’ - 20’
Mature Width: 8’ - 12’
Growth Rate: Moderate
Hardiness: 20-25 degrees F
Exposure: Full Sun
Leaf Color: Ash Gray
Shade: Filtered
Flower Color: Dark Purple to Deep Blue
Flower Shape: Pea Shaped Petals
Flower Season: Early Summer
Thorns: Yes
Propagation Method: Seed
Sizes Available: Not Produced at AZT
Looking like a frozen column of smoke rising improbably from an austere desert wash, it is obvious that Smoke Trees are aptly named. With the unique arrangement of dense, ash gray branches and short-lived gray leaves the tree has an unmistakable billowy appearance that draws the eye to its unusual form and color. Smoke Tree (Psorothamnus spinosus) is native to dry, sandy washes in southwestern Arizona and southeastern California at elevations below 400 to 500 feet. In these desert conditions it matures to a height of anywhere from 12' to 20' with a spread approaching 8' to 12'.
Smoke Tree, also called Smoke Thorn Dalea and Corona-de-Cristo, is highly drought tolerant and best adapted to decomposed granite or sandy soils that are well-drained and very low in organic matter. It tolerates full sun, grows slowly even under ideal conditions and is hardy to 20 to 25 degrees F. Small gray leaves, 1/4 to ½ inch long, are short lived and generally appear for a few weeks in response to fall and winter rains. The form and texture of the canopy are created by the repeated, forked branching of the tree as it grows. Branches and branchlets are sharp tipped and stiff. The vast majority of photosynthesis is carried out by these branchlets with the chlorophyll found just below a surface layer of dense gray hairs.
In stark contrast to the generally subdued appearance of this tree, it produces the most remarkable flowers. Small, dark purple to deep blue pea-like flowers, up to ½" long, appears in clusters at or near branch ends. Emerging from the purple flower petals are bright orange anthers. Flowers can lend a brief, brilliant blue cast to the appearance of the tree. Flowers appear from June to July with buds developing in April and May. Flowers are followed by single seeded pods. Smoke Trees bring a unique and delicate texture and remarkable flowers into the landscape.
It works well as a single accent or specimen tree, in groupings, as a transitional tree back to native desert on the perimeters of the landscape or to cast elaborate shadows against structures or walls. It offers strong contrast to dense, green, canopied, desert tree species and blends well with cacti, boulders and hardscape elements. Locate Smoke Trees within the landscape with care and appreciate that they require little or no supplemental water (one study reported that under green house conditions Smoke Trees survived on four irrigations in 2 ½ years). Understory planting or adjacent trees and shrubs that require regular irrigation will be incompatible. Prune trees for shape or to enhance natural form and texture.
The information provided here was gathered from research literature published by the University of Arizona, other professional landscape and horticulture organizations and our experience at Arid Zone Trees. Always consult local landscape experts for recommendations for your specific area.