Updated: Aug 19, 2021
Albizias fly in and out of favor as the wind blows, or more succinctly, whenever we find California's droughts in the news. Their toughness means they can thrive and even spring up almost anywhere; near my office is a beautiful specimen sandwiched between a freeway sound wall and a frontage road, seemingly ignoring any need for water.
Speaking of freeways, I recall a number of these silk trees planted on the slopes above Highway 101 in Marin, just adjacent to what used to be known as the Harkle Road wind turbine, an odd Mid-Century Modern round house crowned with a horizontal windmill type structure made from industrial canisters that slowly spun in the breeze. The trees, with their round umbrella shapes, mimicked the house design, leading me to wonder if Cal Trans was playing with borrowed scenery. Both Jetson-style house and trees are still there (attesting to their durability), but the wind turbine is no more.
These locations, often neglected and lacking in water, seem to leave the trees undeterred. Known for its invasiveness in wetter regions, such as Hawaii and Florida, A. julibrissin is not considered to be a problem in California. Sure, you might find occasional isolated seedlings, such as my frontage road survivor, but such finds are manageable.
Their real value is an ability to provide light and layered shade, highly suitable for patios with their aforementioned umbrella appearance. In the right location, their silhouette is quite sculptural, lending themselves to a number of garden aesthetics, from Asian-inspired to desert or Mediterranean (they are native to a wide region from Iran to Japan). Just be mindful of their messiness, dropping flowers (spring), leaves (fall), and legumes (winter/spring), and the cycle begins again. Thankfully, the flowers and leaflets are small and therefore do not contribute to a major clean-up regimen.
Botanical Name: Albizia julibrissin
Albizia: Honoree, 18th century naturalist, Filippo degli Albizzi
Julibrissin: Persian, gul-ebruschin, for floss silk (referencing the delicate flower appearance)
Common Name: Silk tree; mimosa
Family Name: Sapindaceae
Origin: Iran to Japan
Positioning: Lawn, riparian (may lead to reseeding), patio, street, slope, forest edge
Garden Themes: Asian, Mediterranean, desert, pollinator, woodland
Uses: Shade tree, specimen, street, accent
Type: Deciduous tree (multi-trunk or standard)
Form: Vase, umbrella, spreading (with horizontal branching)
Size: 50' wide x 40' tall (see specific cultivars for differing sizes)
Outstanding Feature(s): Flowers, shade value
Bark: Dark gray and smooth
Type: Bi-pinnately compound
Shape: Elliptical to oval (leaflets are oblong, from 10-25 pinnules; 50-60 leaflets)
Color: Medium green, slightly lighter underneath turning shades of gold, red to orange in fall (see specific cultivars for variation)
Flower: Summer. Puffs of stamens, white to pink in apical clusters. Fragrant (close range)
Fruit: Autumn into winter or longer. Legume, deep brown
cultural requirements, tolerances & problems
Sunset Zones: 4-23
USDA Zones: 6-9
Light: Full sun to part shade
WUCOLS SF Bay Area Hydro Zone: Low
Texture: Sand, loam, clay
Moisture Retention: May dry between watering
pH: Highly acidic to highly alkaline
Tolerances: Drought, heat, poor soils, saline
Problems: Considered short-lived elsewhere
Branch Strength: Medium to weak
Insects: Borers, aphids
Disease: Armillaria, fusarium, root rot
citations & attributions
Bayton, R. (2019). The Royal Horticultural Society's the Gardener's Botanical: An Encyclopedia of Latin Plant Names. London: Mitchell Beazley.
Big Island Invasive Species Committee. "Albizia." Accessed on July 1, 2021, from https://www.biisc.org/albizia/.
Center for Aquatic and Invasive Plants. "Albizia julibrissin." University of Florida. Accessed on July 1, 2021, from https://plants.ifas.ufl.edu/plant-directory/albizia-julibrissin/.
Missouri Botanical Garden. "Albizia julibrissin." Accessed on July 1, 2021. http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?taxonid=280416.
Norris Brenzel, K. (Ed.). (2012). The New Sunset Western Garden Book. New York: Time Home Entertainment, Inc.
NC State Extension. "Albizia julibrissin." North Carolina State University, Raleigh. Accessed on July 1, 2021, from https://plants.ces.ncsu.edu/plants/albizia-julibrissin/.
Urban Forest Ecosystems Institute SelecTree. "Albizia julibrissin Tree Record." 1995-2021. Cal Poly State University, San Luis Obispo. Accessed on July 1, 2021. https://selectree.calpoly.edu/tree-detail/147.
Water Use Classification of Landscape Species. "WUCOLS IV Plant List." University of California, Division of Agriculture and Natural Resources, Davis. Accessed on June 28, 2021.
All photos by TELCS.