California landscape designers, give this tree more attention. We have a specimen at West Valley College (shown below), which is just starting to show its swollen trunk. B. populneus is a type of bottle tree, known for their dramatic trunks that indeed have silhouettes like glass bottles. This species, however, appears to not have the strong bottle profile, even in photos of clearly older specimens. Regardless of their size, their trunk is where they store their water, lending themselves to periods of drought (i.e. California's situation). Not particularly fast growers; the advantage of slow growth is low maintenance with just a little annual clean up. If given proper spatial allowance, this bottle tree is its own sculpture but can also provide a lush canopy. As the species epithet suggests, the poplar-like leaves flutter in the wind, another attractive quality to admire.
Cal Poly's Urban Forest Ecosystems Institutes states a hardiness to 25° F., which the San Francisco Bay Area has historically experienced over time. West Valley College sits on a rise toward the Santa Cruz Coastal Mountains, which might aid in limiting cold air found in lower valley floors. In the time I have been teaching at the college, I have not seen any frost damage. Observing it prompted me to plant another species type, Brachychiton rupestris, in our home garden, which has performed well so far. What this all suggests is either a higher cold tolerance or more mild winters, opening the doors to specifying these unusual trees in California's landscape projects.
West Valley College Campus Location: Brachychiton populneus
Administration (west planter)
Long: 122° 0'43.52"W
Botanical Name: Brachychiton populneus
Brachychiton: Traditional Latin name for alder tree
Populneus: Red, as in the interior hardwood
Common Name: Bottle tree
Family Name: Malvaceae
Positioning: Background, in silhouette
Garden Themes: Mediterranean/dry, sculptural, sub-tropical
Uses: Specimen, winter interest, shade, street tree (be cautious about visibility/space), screen
Type: Evergreen tree
Size: 50' tall, 30' wide
Outstanding Feature(s): Form (trunk)
Bark: Light gray, slightly textured
Color: Dark green
Surface: Smooth, glossy
Flower: Spring to summer. Clusters of small bell-shaped flowers, showy, white exterior, spotted pink/dusty rose interior.
Fruit: Summer to fall. Brown follicle.
cultural requirements, tolerances & problems
Sunset Zones: 12-24
USDA Zones: 8-11
Light: Sun to partial shade
WUCOLS SF Bay Area Hydro Zone: Low
Texture: Sand, loam
Moisture Retention: Dry between watering cycles
pH: Slightly acidic to highly alkaline
Tolerances: Drought, armillaria
Branch Strength: Strong
Insects: Invasive shot hole borer
Disease: Root rot
Plants For A Future references B. populneus with edible seeds used as a coffee substitute. Not recommended by TELCS, as we have no experience with coffee of any kind.
citations & attributions
Bayton, R. (2019). The Royal Horticultural Society's the Gardener's Botanical: An Encyclopedia of Latin Plant Names. London: Mitchell Beazley.
Growing Native Plants. "Brachychiton populneus." Australian National Botanic Garden, Acton. Accessed on August 12, 2021, from https://www.anbg.gov.au/gnp/interns-2002/brachychiton-populneus.html.
Landscape Plants. "Brachychiton populneus." American University, Beirut. Accessed on August 12, 2021, from https://landscapeplants.aub.edu.lb/Plants/GetPDF/91dc9273-d4d0-4985-b0f6-ad2e04803fff.
Norris Brenzel, K. (Ed.). (2012). The New Sunset Western Garden Book. New York: Time Home Entertainment, Inc.
Plants For A Future. "Brachychiton populneus." Plants For A Future, Dawlish. Accessed on August 12, 2021, from https://pfaf.org/user/Plant.aspx?LatinName=Brachychiton+populneus.
SelecTree. UFEI. "Brachychiton populneus Tree Record." 1995-2021. Cal Poly State University, San Luis Obispo. Accessed on Aug 12, 2021, from https://selectree.calpoly.edu/tree-detail/214.
Water Use Classification of Landscape Species. "WUCOLS IV Plant List." University of California, Division of Agriculture and Natural Resources, Davis. Accessed on July 27, 2021.
All photos by TELCS.