Scientific: Washingtonia filifera
Common: California or desert fan palm
Family: Arecaceae
Origin: Native to desert springs and tectonic fault lines in southern Nevada (along the Colorado River drainage) into far western Arizona and eastern California and south into Baja California, Mexico. Desert fan palm is even cultivated in St. George in southwest Utah (where it thrives!) and is also found as a landscape palm all the way north into southern Oregon. It is found in California landscapes everywhere west of the Sierra Nevada Mountains up to 3,000 feet elevation. In it's native habitat range it can grow to almost 4,000 feet in elevation and is tolerant of yearly frosts and occasional desert snow. It thrives (producing thickets) within it's native range in desert riparian ecohabitats that are fire dependent.

Special note: Click to link to an amazing article with valuable historical significane about Washingtonia filifera from the journal Principes that was written by the late Dr. Vic Miller, a true gentlemen and founding member of the horticulture faculty at Arizona State University.

Pronounciation: Wash-ing-TOE-nee-a fil-i-FER-a

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

Landscape Use: Parkways, very large and open landscape spaces, stunningly large vertical accent even when not yet full grown, and even a small container bonsai.

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

Growth Habit: Single trunk to 60 feet, massive.

Foliage/texture: Large fan shaped fronds with hairy filaments (especially on younger fronds of young palms) extending from frond margin; fronds more generally more gray-green than the green fronds of the Mexican fan palm; coarse texture.

Flowers & fruits: Cream-colored panicle cluster of flowers in June; oblong fruits ripen to a purple black color in fall, edible tasting much like date palms fruit but with much less 'bang-for-the-buck' given their micro fruit size.

Seasonal color: None

Temperature: Hardy to 15o to 20oF.

Light: Full sun

Soil: Tolerant

Watering: Water deeply but infrequent, especially during unusually dry periods.

Pruning: Prune off old fronds and flower panicles on an annual basis in summer after flowering (later June), commonly called "skinning".

Propagation: Germination of fresh seed is easy. California fan palm is self-compatible or apomictic. Germination is so easy that it will readily reseed and naturalize in Phoenix urban landscapes, along canalways, and in local Phoenix riparian areas where only small amounts of water are present. Seeds dispersed by birds.

Disease and pests: Budrot fungus (Penicillium vermoeseni also known as Gliocladium vermoeseni) is a potentially lethal problem affecting the terminal shoot meristem. Spray bordeaux as a preventative or tree inject with a systemic fungicide such as Mauget's AbasolTM. California fan palm is subject to lightning damage in Phoenix during summer monsoon storms.

Additional comments: This massive fan palm is not for small landscape spaces; always remember its eventual massive size with considering its placement location at any landscape site. California fan palm is arguable partially self-shedding (though the Miller article linked above proves that it is not) and can be most easily distinguished from Mexican fan palm by noting its mid-trunk caliper which is always greater than 12 inches. In historical terms, California fan palm has been used as a landscape palm in Phoenix since the city's inception. Today, older specimens may be seen lining both sides of streets in older neighborhoods throughout in the city.

Final interesting note: Up to 26 feet in height the desert fan palm produces fronds whose petioles have a dense arrangement of hooked spines on the petiole ridges. However, fronds produced by the palm above 26 feet in height have no petiole spines. Why? Paloebotanists believe that this is a protective mechanism the desert fan palm once used against the herbivory of ancient large mammals that were able to reach to about 24 feet in height to graze on the palm fronds.