Washingtonia Palms: Wonders or Weeds?By Geoff Stein (palmbob)
December 8, 2010
Mexican Fan Palms (Washingtonia robusta) are one of the most commonly grown palms in the world, and are definitely the most commonly grown palm that has little or no economic food value. The reason for this is adaptability, extremely rapid growth and universal availability. I cannot think of another palm with this growth rate potential that is as hardy and easy to grow as a Washingtonia robusta. There are some palms that do grow faster in the tropics, but they pale in comparison to this one's hardiness and ease of growth.
There are two species of Washingtonia currently, though there has been some debate whether they should be considered one species and two subspecies, as floral differences are minor to non-existent. The California Fan Palm, Washingtonia filifera, is phenotypically a different palm, having not only a different appearance, but a different growth rate and very different adaptability to various climatic situations (see table below). But most people think of the Mexican Fan Palm, Washingtonia robusta, when they think of a typical fan palm. This species is native to inland northwestern Mexico and Baja California and possibly its native range extends into southern California. It is hard to know for sure now as this palm has grown a long time as an ornamental and it is now found all over the southern California landscape. Seed distribution via bird droppings have allowed this palm to become naturalized in areas where it is very unlikely anyone purposely planted them, but it is not known for sure how long they have existed in some of these remoter areas.
Washingtonia robustas (left) Washingtonia filieras (right)
The Mexican Fan Palm, as mentioned earlier, is a very fast-growing palm, growing faster than most any other palm that can be grown in southern California. One exception might be Caryota urens (the Giant Fishtail Palm), which has been known to grow from a seedling to over 60 feet in just five years, a feat which would very unlikely be surpassed by the happiest Washingtonia. Syagrus romanzoffiana (the Common Queen Palm) is similarly a very fast growing palm, but not as fast as some Caryota urens can grow. Even Phoenix canariensis has been known to grow at a relatively fast pace. Both Syagrus and Caryotas top out at a certain point and are soon eclipsed by Washingtonia robustas (and Phoenix canariensis and P. dactylifera or Date Palms, to some degree) and can grow upwards of 100 feet tall or maybe even a bit more. Washingtonia filifera usually do not get much taller than 60 to 70 feet and take much longer to get there than any of the above mentioned palms. It is still a moderately fast grower, particularly in comparison to the growth rates of most of Mediterranean-grown palms.
Caryota urens, a Fishtail palm, is a very fast growing palm (left); Phoenix canariensis (and hybrid on right) are also fast... but you can see the surrounding Mexican Fan palms towering over even these very tall palms (right)
Date Palms (Phoenix dactyliferas- left photo) and the common Queen Palm (Syagrus romanzoffiana- right photo) are also two relatively fast growing palms in a non-tropical climate
Washingtonia robustas are also among the easiest of the palms to grow. Often it is keeping them from growing that is the gardener's major issue. Dispersal by bird droppings is rampant and seedlings end up in almost every yard in the southland eventually, particularly below where birds tend to roost, such as signposts, power lines, telephone poles and other trees. More time and money is probably spent by the city of Los Angeles removing Washingtonias than planting or possibly even trimming them. It is remarkable how well adapted this palm is to growing anywhere its germinated seed ends up, often growing in lawn-like numbers in cracks and crevices along streets, sidewalks and parking lots. They require very little water to get started, and once established require very little water to grow. This is one of the most drought tolerant palms one can grow in cultivation. However, even this palm needs some water. One can see dessicated and very sad looking palms in the desert that eventually died due to lack of water. Yet few other palms even come close to getting along that far- far in terms of growth with little water, and far in terms of distance from the mother palm. Washingtonia filifera, it has been argued, is even more drought tolerant, evidenced by large populations of this palm growing in the deserts of southern California where which it is a native (though it grows there almost exclusively over areas of shallow ground water).
Palms with hopeless futures growing in itty bitty cracks in a side walk and parking lot. Eventually the city will have to remove these palms, or they will simply outgrow their few roots
Mexican Fan Palms typically grow fairly straight up, but as they get over fifty feet or more in height, they tend to sway a bit and often develop permanent curves in their trunks. I suspect these curves are due primarily to wind exposure, but it seems uncanny how long avenues of planted palms will have almost the exact same curves and lean almost precisely towards the coast (unless grown right along the coast where they tend to be a bit more stunted in their growth patterns). I cannot help but wonder if the direction of the light is also a contributing factor to their lean westward. This curving of the trunk is a Washington robusta feature only, with the stouter-trunked Washingtonia filiferas growing as straight up as Greek columns. One of the ways one can tell the two apart is by their trunk shape and thickness (though this is somewhat relative, particularly due to the common occurrence of hybrid palms in cultivation).
These old Washingtonia robustas (left) show a typical lean toward the ocean; right are a row of old Washingtonia filiferas growing straight up and down
obviously not all Washingtonia robustas develop curved trunks (left) but some can develop exceptionally curved trunks (right)
Unless pruned such, Washingtonia palms tend to retain a large, dense skirt of leaves (California Fan Palms less so in more coastal locations). As they age, these leaves often are blown free leaving behind a bare, ringed, grey trunk. Very tall trees rarely retain much of a skirt at all, but shorter palms, particularly the California Fan palms in inland situations, will retain an incredibly thick petticoat of dead leaves. One of the alternate common names for the California Fan Palm is Petticoat Palm. These skirts are a potential hazard, both in terms of public health and safety, as well as a hazard for other surrounding plants. Palm petticoats are an excellent hiding and roosting place for all sorts of birds and rodents. A palm across the street from me where I used to live was a home to a family of barn owls. But not all residents are as beneficial. Rat populations can be enormous in some un-groomed palms. Pigeons live or roost in them commonly and their droppings can often contain fungal spores that are serious health hazards to people and pets alike. Falling leaves can injure pedestrians and damage property below. It may not sound all that serious to get hit by a falling Washingtonia leaf since, after all, they weigh barely a pound if that and, if well dried, rather float to the ground than plummet. But the leaf petioles are extremely well armed with large, hooked, very sharp teeth and can do very serious damage if one is hit by a falling or blowing one. Falling leaves also damage plants below and can make a huge mess requiring hours of clean up. They also fall in streets creating a driving hazard. It is this reason that most homeowners and landscapers pay thousands and thousands a year (or daily, if you're the city of Los Angeles) to keep these palms pruned, just so this falling leaf situation won't occur. Additionally petticoats of dried leaves are extremely flammable and can be a real fire hazard during the dry months of the year.
Washingtonia filifera in habitat showing thick petticoats (left); Washingtonia robusta palms that have retained their petticoats, too, (right)
Palm on left is showing some natural loss of petticoat; right is photo fo two Washingtonia robustas, one with a petticoat, and one that had it mostly removed
Messes typical after heavy winds from falling leaves
From an ornamental standpoint, a thick petticoat can be a good look for a palm, but I think most people think of a bare or pruned trunk, and prefer one, when they think of a Mexican Fan Palm. Some professionals will cut the leaf bases off entirely leaving a trunk bare and somewhat scarred by the saw marks left behind. But most privately owned palms are not trimmed that way as that often requires special equipment and experience, so most owners just cut the leaves off at the trunk and leave the leaf bases wrapped around to dry on the trunk. This leaves behind a somewhat ornamental patchwork of split leaf bases that give the palm a different look than the more commonly displayed bare trunk. However, this patchwork of leaf bases will eventually start to loosen and fall also, particularly on older palms, and the problem of clean up and safety may become a burden.
left is a photo of Washingtonia filifera on left with poorly trimmed petticoat next to a Washingtonia robusta, also with a trimmed trunk... but the retained leaf bases have begun falling off by themselves about the level of the crown of the other palm; photo on right shows closer shot of thatchwork trunk after pruning off the leaves only
palms in front yard of residence with all trunks pruned simply; closer shot of thatch-like leaf bases on trunk
palm on left has been professionally trimmed showing the pale, exposed naked trunk (not sure why job was not finished...); palm on right shows leaf bases fallen off by themselves, thanks to gravity, wind and general exposure, while lower leaf bases remain on trunk (these will eventually fall away)
From a nitpicky, detail point of view, the Fan Palm's leaves are palmate for the most part, but more accurately, these leaves are mildly ‘costapalmate'. A costapalmate leaf is one in which the leaflets do not radiate out from a single central point as they would on a fan, but there is a ‘midrib' of origin with the distal leaflets radiating out from the distal end of the midrib and the proximal leaflets radiating out from the proximal midrib. This midrib makes the leaf folded somewhat giving the leaf a more three-dimensional shape, rather than just a simple, flat palm shape. But relative to most of the completely costapalmate palms, such as Sabals or Hyphaene, or even some Livistonas, Washingtonias are relatively flat and fan shape in comparison.
Typical Washingtonia leaf (photo Chamma)
Left is a young Washingtonia robusta showing nearly a perfect fan leaf; right shows a Livistona chinensis (Chinese Fan Palm) with a much greater degree of Costapalmate leaf
this Hyphaene leaf shows the curve of a true costapalmate leaf
The leaves of Washingtonias are typically bright green though the Washingtonia fififera leaves are a bit more sea green in many individuals. This is not a reliable distinguishing point, but can help somewhat in telling the two species apart. The leaves have fibrous filaments that peel away from the edges of the leaflets giving the leaves a sort of hairy look, especially in seedlings. Washingtonia filiferas tend to be a bit more fibrous or hairy than Washingtonia robustas. Another common name for California Fan Palms are Cotton Palms because of the cottony fibers on the leaves. The filifera name refers to the fibers (or ‘filiferae'). As seedlings, Washingtonias have stiff leaflets but as they age, the leaflet tips start to droop. This change leads some unfamiliar with these palms to assume there are two different species involved. Both have large, dangerously sharp, strong hooks or teeth along the petioles but the Mexican Fan Palms have a reddish brown coloration at the base of the petioles that extends down most of the length of the petiole, while California Fan Palms have completely green petioles. This color distinction is fairly consistent between pure species, but the great prevalence of hybrid palms (called Washingtonia ‘filabustas') muddies this distinction somewhat, with some hybrids being mostly green and some being very red-brown).
left is an exceptionally cottony seedling, showing a lot of fiber on the young leaves; right shows a Washingtonia robusta and the coloration of the leaf bases
Washingtonia robusta colors and showing larger, saw-teeth on petioles
Washingtonia filiferas show no red color along petioles
Younger palms retain a lot more leaves, but with age, only the crown holds leaves
Though both palms are very cold hardy, down to around 20F, there is a slight greater cold tolerance, at least to arid cold, in the California Fan palms, of maybe three to eight degrees F. From a humidity tolerance standpoint, the California Fan palms are much more sensitive to high humidity and here in California often struggle when grown near the coast. They are also much more prone to rot when grown the sloggy, poorly draining soils. Additionally they have a much higher rate of bud rot from exposure of their crowns to moisture. It is not uncommon to see mature dead California Fan Palms that have died for no obvious reasons, far below their ‘terminal height'. This is a rare occurrence in the Mexican Fan Palm. Mexican Fan Palms can be readily grown in Florida and Hawaii, as well in other tropical, humid areas of the world, while the other species struggles and almost invariable fails to survive in such climates. Some have said the hybrid Filabustas have fairly good humidity tolerance and even better cold tolerance to either parent, but I do not know if that is really true.
Washingtonia robusta in Thailand (left) and as street trees in Florida (right)
Shots of Washingtonia filifera that for unknown reasons, just rotted and died... rarely see this in Washingtonia robustas unless overtrimmed
Extreme heat is not much of a problem either with both palms growing well in inland California and Arizona where daytime temperatures over 125F rarely are a problem, though the California Fan Palm seems a bit more resistant in this area.
These Washingtonia filiferas are in an inland native botanical garden where drought and high heat are the norm
Wind tolerance is very high in both species with Washingtonia robustas leaning substantially in the winds, while Washingtonia filiferas do not bend at all. Though the intense Santa Ana winds do strip the old leaves off these trees, very rarely does one of these palms get blown over, despite their height and exposure to very strong, nearly hurricane force winds. People often fear for their safety or damage to their home from these palms blowing over, but far more damage and injury occurs every year from just about any other public trees growing in southern California, from pines to sycamores. These palms often get blamed unfairly for falling over when they actually rarely do.
shot of my neighbor's tree blowing in a 60mph wind. This tree really leans when the wind blows, but despite its height of over sixty feet, it handles the wind well. The pine behind, however, loses a branch almost every year from the intense winds.
Fertilization is rarely necessary with these palms in southern California where most of the soils are relatively nutrient rich, at least if they have any clay in them. Where I live in California, the soils are mostly clay so these palms have no need for additional fertilizer ever. However, if grown in sandy soils, such as near the beach, or in Florida, they can certainly benefit from fertilization a few times a year. However, this may make them grow even faster and that may not always be the desired effect.
palms in Nevada tend to be a bit stressed from low soil nutrients and drought
Soil pH is rarely an issue with these palms and they grow fairly well in mildly acid soils to extremely alkaline soils (reported even soils with pH over 9).
Watering mature palms is rarely necessary, at least here in California, particularly if not grown in the arid deserts. If in the desert, if there is no ground water, regular watering is recommended. It is difficult to overwater Washingtonia robustas, though they do not tend to grow well in shallow water as many other palms do. But even poorly draining soils of pure clay and rock seem to support this palm fine with very few nutritional or fungal-related maladies. Washingtonia filiferas are more particular and though will also grow in poorly draining soils, they do not like it when those soils are always wet. Too little water will often result in smaller, weaker-looking crowns with less leaves.
Washingtonia robustas are definitely well adapted to growing where there is plenty of water, despite being very drought tolerant
Washingtonia filiferas are more adapted to desert climates, but still need sufficient ground water (as above near this oasis) to survive
Salt tolerance is relatively high for a palm (though not nearly as high as a coconut palm) and Washingtonia robustas grow readily along the beaches all around the world. The salt tolerance of the California Fan Palm might be high as well, but these palms do not like growing near the beach for other reasons (see above).
Light is extremely important for health of these palms and they do not do all that well indoors. However, there is sufficient light often in large malls with a lot of overhead sky lites for these to do quite well as indoor mall palms.
Flowers are virtually identical on both species, being a pale yellow to white along a six foot or more arching inflorescence arising from the middle of the crown. Flowers are bisexual so these palms are monoecious. The flowers are definitely not one of these palms or ornamental attributes and stick out of the crowns like drooping spikes.
Washingtonia filifera showing messy flower spikes (left) and open flowers (right)
Washingtonia filifera in full seed
Germination of the ½" seeds is extremely easy and often rapid. Ripe, fertile seed is easy to come by and usually plentiful year round below most adult palms. Seeds are small and slightly ovoid. These will germinate rapidly with bottom heat, but often germinate nearly as well with little heat at all, just a bit of moisture.
Germination of seed in less than 2 weeks (photo mustangman826)
Young palms do not transplant all that easily, which is surprising as mature palms are known for the ease of transplanting (at least of tolerating transplanting). One needs to support the weight of the palm when digging up and moving larger ones, as cracked trunks usually end up in the death of the palm. This is not a great palm for growing large in order to sell, for several reasons. First, it is quite expensive to move one, usually taking several people, a back hoe and a crane. Secondly it is such a fast growing palm that most can get a large palm from seedling size in less than 10 years, and a very tall palm in 20 years. Frankly, few but wealthy landscapers ever buy these palms at nearly any size, as they are so common and readily available in just about any size already.
Pruning these, as mentioned before, usually requires a professional, at least once mature, who either climbs the palm with spikes and a belt, or, if they work for the city, use a tall crane with a basket. Pruning is quite dangerous as the petioles are so sharp and can snag on ones clothing or skin or even hair when falling, and a newly cut, living leaf is quite heavy. Also these palms get very tall and pruning one without a crane on a windy day at one hundred feet about the ground can be a dizzying experience I am sure, and a very risky one as well, as these are known to sway back and forth a lot. For the same reason, taking one out of the yard can be a risky and dangerous proposition, for the home and plants below as well as trimmer and observers alike.
City worker pruning palms in a crane cab
Trimming the leaves is generally recommended to be done more frequently and less severely than what is actually usually done in cultivation. And the reason it is usually done so drastically is the costs involved in trimming the very tall specimens. So instead of trimming them four to six times a year as probably should be done , most get trimmed maybe two times a year and get butchered in the process to the point where only a few leaves are left sticking like small fountains out the top of the palms. Amazingly these palms often tolerate this abuse, but sometimes this can weaken the palm enough that it will succumb to something else, or starve itself from lack of photosynthetic activity. It is recommend ideally that these palms be pruned only as far as cutting the leaves that are parallel to the ground and not any higher. This less severe pruning is unlikely to weaken the palm in any way.
Palms way over-pruned
Removal of palms is a common activity in California as they show up everywhere. Removing small palms is fairly easy as they one can pull them out by the leaves, or they will snap off at the roots. This is OK as they will rarely grow back after this process. Round Up has little effect on palm seedlings I have discovered. However, as the palms start to make a trunk, they are not so easy to remove. Just topping them will sometimes result in complete recovery (I think this is fairly unique in the palm world). The taller and older the palm, the less like topping it will result in surival, though. But then one still has to deal with the dead trunk. Some elect to just leave it there and dead trunks seem to remain fairly solidly in place of many years, often being used as perches for epiphytes or for landscaping purposes. Most of the time they just get cut down to a stump, which will eventually rot out over many years. But until then, the stumps are useful benches or tables.
Here are shots of a palm that was beheaded, yet it's coming back... what other palm can do that? Not sure why the city did not just cut it off at the base... or did they just want to do a super trim, and if it came back, so be it. Still, the palm is in a bad location so they will have to remove it someday soon (under a traffic light)
This Washingtonia (left) had ALL its leaves cut off... but it came back, too; right photo shows successful removal evidence
There are several palms growing in cultivation in Southern California, Texas, Arizona and Florida that can look like Washingtonia palms. Below are a few of the ‘imposters' one might encounter.
Brahea brandegeis look a lot like smaller Washingtonia robustas, but the tell-tale retained leaf bases are not split. Photo on right shows a Brahea brandegei with a long skirt making it really hard to tell from the Washingtonias (behind to to the right of them), but again, the unsplit leaf bases give them away.
Brahea edulis are probably the most commonly planted look-alike, at least in southern California. These don't retain leaf bases so you can use that as clues, but the leaves are more costapalmate and flowers are very different. After a while you notice the overall shape of the palm is somewhat sqatter and the crowns are more full with less droopy leaflets
Livistona nititda can look a lot like a Washingtonia robusta, especially when young... but as it ages (left) it shows the unsplit retained leaf bases; right is a Sabal palmetto which has an overall appearance like a Washingtonia, and even has split retained leaf bases, but its leaves are very costapalmate and there are no teeth on the petioles
Differences between Washingtonia robusta and Washingtonia filifera:
Ht. Med. Climate
100 feet plus
Straight to curving or ‘s' shaped
Retained until very tall
Usually shed unless desert conditions
Red-brown fading to green at leaf
Densely leaved (often over 30 leaves)
Sparsely leaved 8-20 leaves (more in oasis desert conditions)
Deep shiny green
Medium to light green
Few to moderately fibrous
Moderately to very fibrous
Moderate (for a So California palm)
Moderate to good
Poor as it ages
Mexican Fan Palm, Skyduster
California Fan Palm, Desert Fan Palm, Petticoat Palm, Cotton Palm
Washingtonia robusta on left and all the rest are Washingtonia filiferas
Comments: personally I think this palm gets an unfair bad rap, mostly due to its weed-like nature, pest-harboring capabilities and messy leaf dropping. In addition, palm enthusiasts detest its commonality, thinking of these as ‘poor man's palms'. But whether you like them or not, mature, towering Sky Dusters are impressive and ornamental sights. They add so much beauty to the otherwise stark concrete landscape of southern California.
To me, the photo on the left says elegance and California, while the ugly trees on the right, planted all over southen California just show some archaic brain trying to relive its former life on the east coast by planting ugly reminders of the trees there, here in California. I realize some sycamores are native to California, but most landscaped sycamores are sickly and pathetic year round.
Even though they are common and may be weeds, their beauty is hard to deny