Scientific: Washingtonia robusta H. Wendl. (synonum: Washingtonia filifera var. robusta, Washingtonia gracilis Parish, Washingtonia sonorae S. Wats
Common: Mexican fan palm
Family: Arecaceae
Origin: Southern Sonoran desert, Baja California

Pronounciation: Wash-ing-TOE-nee-a row-BUS-ta

Hardiness zones
Sunset
8, 9, 11-24
USDA 9-11 (arid and semi-arid regions best)

Landscape Use: Parkways, streetscapes, towering vertical accent. Not the best palm for residential areas.

Sustainable Landscape Solutions: Tired of paying big bucks to arborist companies to prune off those dead Washingtonia fronds each June? Need a place in your landscape to park your backside and enjoy an ice-cooled glass of refreshing green tea during a hot Phoenix summer afternoon? Then why not instead opt for repurposing that cash sucking, ginormous Mexican fan palm in your yard into your very own 'palm chair'?

Form & Character: Evergreen fan palm, upright, strong vertical effect, oasis

Growth Habit: Single trunk to 100 feet, slender girth.

Foliage/texture: Large fan shaped bright shiny palmately compound fronds, ends of mature frond pinnae characteristically droop, coarse texture

Flowers & fruits: Cream-colored panicle cluster of flowers in June, oblong fruits ripen during fall, non-edible.

Seasonal color: None

Temperature: Hardy to 20oF.

Light: Full sun

Soil: Tolerant

Watering: Will take drought and appears on most low water use list; however, this palm does best with moderate and deep supplemental irrigations during summer.

Pruning: Prune off old fronds and flower panicles on an annual basis in early summer immediately after flowering. Don't over prune!. Instead, prune off only enough fronds so that at least 1/3rd of the canopy remains when the job is done. Sadly ignoring this important rule-of-thumb, tree worker wannabes inevitably get too fired up and butcher these palms leaving in their wake a comical landscape that can compete for attention with the best old Disney cartoon.

Danger Alert: Removal of old fronds, especially on specimens with significant skirts of dead fornds, is a dangerous and sometimes lethal activity. Skirts have been known to suddenly slough off and onto climbers suffocating them to death.

Propagation: Easy by seed, very prone to naturalize in Arizona and southern California landscapes. Check out this Mexican fan palm growing out of a Grevillea robusta at a cemetery in southern California.

Disease and pests: Less prone to budrot (Penicillium vermoeseni) fungus than W. filifera. No cure because the crown is usually too high to feasibly treat even preventatively. Subject to lightning injury and fire during summer.

Additional comments: Mexican fan palm's extensive, highly fibrous root system and tall slender habit means that it is not a palm tree for small landscape spaces; use with discretion. Mexican fan palm is arguable partially self-shedding and its mid-trunk caliper (without persistent leaf sheaths attached) is less than 12 inches. Some think that Washingtonia robusta can cross pollinate (hybridize) with Washingtonia filifera to produce an offspring of intermediate trunk caliper making proper visual identification sometimes difficult. Often very large specimens are successfully transplanted and relocated.

A sad tale: The most unique planting of palms on the Arizona State University (ASU) campus was the double row (palm allee) of Mexican fan palms along Palm Walk on the ASU Main campus. This double Mexican fan palm alle stretched from University Blvd south to the Student Activity Center. The northern half of the alle was planted in 1916. The southern half stretching from the Life Science building complex south to the Student Recreation Complex were planted between 1937 and 1939. They were about 3 feet tall at the time of planting. Sadly, these tall and majestic pillars were ill-advisedly replaced in 2016 with Phoenix dactylifera (date palms). The "official" reason given for their replacement was that the Mexican fan palms were "near the end of their life cycle at 100 years". This is in fact false. Mexican fan palms have been well documented in the scientific literature to live up to 500 years (Bullock and Heath, 2006)!

Citation: Bullock S and D Heath, 2006. Growth rates and age of native palms in the Baja California desert. Journal of Arid Environments 67(3):391-402.