Washingtonia robusta

Updated: Aug 5


Few trees in the California landscape, such as oaks and redwoods, have reached icon status, and the infamous palm is one of them. Its infamy will be explained momentarily. For Washingtonia robusta in particular, palm-lined avenues throughout the cinematic southlands has elevated its status, competing with our native species, Washingtonia filifera (see comparative photo below). The competition was brief, since W. robusta, or Mexican fan palm, soars high into the sky, lending itself to SoCal sunsets over the endless Pacific.


W. robusta (left), W. filifera (right)

A telephoto shot of a row of lanky palms became shorthand for L.A. - America's dream factory, the most filmed locale in the world. Long after the city's street tree division gave preference to other species and genera, private developers, architects, and landscape designers utilized Mexican fan palms for the mass communication of desirability. The "L.A. look" transcended Los Angeles: shopping malls, gated communities, and casinos...mimicked and exaggerated the fashion for high-rise fronds (p. 385).


~ Jared Farmer (2013)


Lesser known are the thriving palms (primarily W. robusta and Phoenix canariensis) of NorCal, flanking Victorian doorways amidst pinots, cabs, and syrahs, scatterings in the San Francisco Bay Area, and random allées or parkway plantings, such as Stanford's Palm Drive (where both W. robusta and mostly, P. canariensis, are planted) or San Jose's Palm Haven neighborhood. They mark our history, but their symbolism within the California landscape is changing.


Namely, the past investment in W. robusta as street trees is coming to a close. I turn to Evan Meyer of UCLA's Mildred E. Mathias Botanical Garden for his discussion, citing their senescence coupled with pests and diseases making W. robusta a liability for Los Angeles and other communities. Those liabilities extend to heavy fronds crashing to the ground from 60' to 100', barbed with hooked teeth flanking the petiole, rats nesting in the dead fronds still on the palm, and if said palms are not removed through routine maintenance they become a fire hazard. Their status as an invasive species furthers their descent in popularity, though I question this classification in a time of climate change and natural species migration, especially considering its ability to crossbreed with the California native. Washingtonia x filibusta anyone?


So how does all this relate to landscape architects? When a client expresses dreams of a tropical oasis, such as a pool terrace in a hotel courtyard, does the mind immediately think Mexican fan palms? It might, and nurseries still sell them for the uninformed and the careless. Should we stop using them in California landscapes? Here are questions to resolve: 1) Will their location be out of harms way when/if palm fronds drop? 2) Will the maintenance practice routinely remove dead palm fronds, not matter how high the reach? 3) Are we okay with a 75 to 100-year life span at best, less if stressed, and its possible contribution to the invasive species population? If designers can answer these questions and still feel W. robusta is a viable addition to their design, then specify away!


West Valley College Campus Location: Washingtonia robusta

Community Education (driveway)

Lat: 37°15'58.11"N

Long: 122° 0'37.50"W

facts

Botanical Name: Washingtonia robusta

Washingtonia: Honoree, first U.S. president, George Washington

Robusta: Growing strongly, hardy

Common Name: Mexican fan palm

Family Name: Arecaceae


Origin: Baja and Sonora, Mexico


design considerations


Positioning: Background, coastal

Garden Themes: Oasis, sub-tropical/tropical, water, desert/dry

Uses: Accent, boundary, landmark, specimen

identifying characteristics


Type: Palm

Form: Erect, round

Texture: Coarse

Size: 100' tall with 10' canopy at top only


Outstanding Feature(s): Height


Bark: Light red-brown to gray (remaining leaf petioles may obscure bark)

Leaf: Large, sharply hooked thorns along petiole

  • Type: Pinnately compound

  • Arrangement: Alternate

  • Shape: Palmate

  • Margin: Entire

  • Color: Dark green

  • Surface: Smooth, glossy

Flower: Summer. Long panicles of cream colored flowers hang within and below fronds. Fragrant and showy.

Fruit: Summer to Autumn. Clusters of small drupes, brown, edible but with little flesh.


cultural requirements, tolerances & problems


Sunset Zones: 8-10, 11-24; H1, H2

USDA Zones: 9-11


Light: Full sun

WUCOLS SF Bay Area Hydro Zone: Low

Soil:

  • Texture: Sand, loam

  • Moisture Retention: Well-drained

  • pH: Slightly acidic to highly alkaline

Tolerances: Texas root rot, heat, drought, wind, deer

Problems:

  • Branch Strength: N/A

  • Insects: South American palm weevil (Southern California)

  • Disease: Fusarium (Southern California)


citations & attributions


Extension Gardener Plant Toolbox. "Washingtonia robusta." North Carolina State University, Raleigh. Accessed on July 29, 2021, from https://plants.ces.ncsu.edu/plants/washingtonia-robusta/.


Hodel, D.R. (July, 2014). "Washingtonia × filibusta (Arecaceae: Coryphoideae), a new hybrid from cultivation." Phytoneuron 2014-68: 1–7. Accessed on July 29, 2021 from http://www.phytoneuron.net/2014Phytoneuron/68PhytoN-Washingtoniahybrid.pdf.


Hodel, D.R., Santos, P. (2020). The New Fusarium Wilt Disease of Palms in California Now Confirmed on Mexican Fan Palms. University of California Agriculture and Natural Resources, Davis. Accessed on July 29, 2021, from https://ucanr.edu/sites/HodelPalmsTrees/files/336533.pdf.


Meyer, E. "Street Plants: Ethnobotany of Inner City L.A." Mildred E. Mathias Botanical Garden, University of California, Los Angeles. Accessed on July 29, 2021, from https://sites.lifesci.ucla.edu/eeb-botgard-new/wp-content/uploads/sites/120/2019/03/StreetPlants_Washingtonia_robusta.pdf.


Norris Brenzel, K. (Ed.). (2012). The New Sunset Western Garden Book. New York: Time Home Entertainment, Inc.


SelecTree. UFEI. "Washingtonia robusta Tree Record." 1995-2021. Cal Poly State University, San Luis Obispo. Accessed on Jul 29, 2021, from https://selectree.calpoly.edu/tree-detail/1471.


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.

https://ucanr.edu/sites/WUCOLS/Download_WUCOLS_IV_List/.


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