Not until I was in my thirties did I visit my first true oasis in the California desert. I knew desert oases were sanctuaries of water, but I had always associated the image with luxuriant tents lined with Persian rugs, tethered camels, dense foliage and refreshing ponds. That's what the silver screen taught me about this exotic landscape. If you have not been to the outskirts of Palm Springs or Palm Desert to experience a local oasis, it is certainly difficult to understand the context where our native California fan palm, Washingtonia filifera, thrives.
Hot as a fired up pottery kiln! Okay, I'm stating the obvious, but there was little to no reprieve from the heat radiating from the nearby rocks and canyon walls. There are places where the palms as so dense that an ounce of shade can be captured, but mostly the desert is a constant reminder of an inhospitable place. Were it not for the trickling water filtering through at the base of the palms, I would have forgotten that I was indeed in an oasis. Which leads me to ponder how California's first hippie, Nature Boy William Pester, found the canyons of Palm Springs such havens of respite, just as the Kamia and Cahuilla people had done for thousands of years before. Those are other stories, but the stories of Pester add another complex association I have with this palm, of German emigrants, hippies, health crazes, and Mid-Century Modern architecture, as explored by author Lyra Kilston for Sun Seekers: The Cure of California (2019). But I digress.
While desert oases may be its native habitat (I recommend visiting Anza-Borrego Desert State Park), California fan palms have left their canyons for more hospitable (for humans) ornamental landscapes. Rather, growers are propagating more native palms for new landscapes. When we moved to the South Bay, I was surprised to see our local Target lined with them in pairs along the store's frontage. So far, they seem to be doing well despite how much further north we are from Palm Springs. Numerous native fan palms can be found throughout the City of San Jose, particularly downtown.
It can be easy to confuse W. filifera with its more popular but classified invasive sibling, W. robusta, but there are some obvious differences. W. robusta, or Mexican fan palms, are much thinner, especially noticeable as their mature height stretches much further to the sky (see second photo below). By contrast, W. filifera seems more reserved, capable of maintaining a human scale in the landscape where we can appreciate its exotic appearance. The challenge in planting them is making sure the soil is compatible.
In a desert environment, the soil is rocky, sandy even, so despite access to water from springs, their roots can breath in the porous soil. If, however, they are planted in, say, the Bay Area's commonly found clay soil, then problems such as rot may occur. The situation can be compounded with regular irrigation resulting in soil staying moist for too long. For designers, this means assessing the conditions before specifying, and either addressing through soil amendments (a temporary solution), designing raised planters with great drainage, or perhaps avoid planting them altogether if soil is indeed a concern.
Both fan palms tend to hold onto their fronds long after they have desiccated. This is a problem in today's California landscapes, where large regions are vulnerable to fire. Maintaining frond removal is certainly a remedy, but that does mean extra cost. If maintenance is not an issue for clients, then this native is one to consider.
Another brief overview from the Jepson Herbarium with footage within a native California palm oasis.
facts
Botanical Name: Washingtonia filifera
Washingtonia: Honoree, first president of the United States, George Washington
Filifera: Thread-bearing, in reference to white hair-like fibers that hang from the fronds.
Common Name: California fan palm
Family Name: Arecaceae
Origin: Native; California deserts, Arizona, northern Mexico
design considerations
Positioning: Background, silhouette
Garden Themes: Desert oasis, native, Mediterranean, tropical aesthetic, urban
Uses: Poolside, park, allée, specimen, grouping
identifying characteristics
Type: Palm
Form: Erect, round canopy
Texture: Coarse
Size: 60' tall, 20' wide at canopy
Outstanding Feature(s): Form
Bark: Red-brown, smooth to lightly furrowed (when devoid of frond remnants)
Leaf: Large, hooked thorns along petiole (leaf bends down and hangs on tree to from a "skirt" along the trunk, a concern for fire and rodent nesting).
Type: Compound
Arrangement: Alternate
Shape: Palmate
Margin: Entire
Color: Medium green
Surface: Glabrous
Flower: Spring. Inconspicuous cream-colored panicles
Fruit: Summer to autumn. Small clusters of black drupes, inconspicuous
cultural requirements, tolerances & problems
Sunset Zones: 11-24; H1, H2
USDA Zones: 9-11
Light: Sun
WUCOLS SF Bay Area Hydro Zone: Low
Soil:
Texture: Sand, loam
Moisture Retention: Well-drained
pH: Slightly acidic to very alkaline
Tolerances: Deer, heat, drought, Texas root rot
Problems:
Branch Strength: Weak
Insects: Scale
Disease: Armillaria, trunk or 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.
Calscape. "Fan Palm." California Native Plant Society, Sacramento. Accessed on September 1, 2021, from https://calscape.org/Washingtonia-filifera-().
Conrad, T. (2019, April 27). Nature boys of Palm Springs had strange and famous lives. Desert Sun. Retrieved on September 1, 2021, from https://www.desertsun.com/story/news/2019/04/27/nature-boys-palm-springs-had-strange-and-famous-lives/3597791002/.
Fire Effects Information System. "SPECIES: Washingtonia filifera." United States Department of Agriculture, Forest Service, Washington D.C. Accessed on September 1, 2021, from https://www.fs.fed.us/database/feis/plants/tree/wasfil/all.html.
Gilman, E.F., Watson, D.G. "Washingtonia filifera: Desert Palm" University of Florida, Institute of Food and Agricultural Services, Gainesville. Accessed on September 1, 2021, from https://edis.ifas.ufl.edu/publication/ST669.
Kilston, L. (2019). Sun Seekers: The Cure of California. Los Angeles: Atelier Éditions.
Norris Brenzel, K. (Ed.). (2012). The New Sunset Western Garden Book. New York: Time Home Entertainment, Inc.
SelecTree. UFEI. "Washingtonia filifera Tree Record." 1995-2021. Cal Poly State University, San Luis Obispo. Accessed on September 1, 2021, from https://selectree.calpoly.edu/tree-detail/1470.
Taxon Report. "Washingtonia filifera." Calflora, Berkeley. Accessed on September 1, 2021, from https://www.calflora.org/app/taxon?crn=8336.
Water Use Classification of Landscape Species. "WUCOLS IV Plant List." University of California, Division of Agriculture and Natural Resources, Davis. Accessed on September 1, 2021.
Photos:
Frond detail: "Washingtonia filifera frond" by Atirador is licensed under Wikimedia Commons.
Palms in desert: "Washingtonia filifera 1" by Stan Shebs is licensed under Wikimedia Commons.
Comparison photo by TELCS.