Mexican fan palm (Washingtonia robusta) is a palm species native to the western and southwestern United States. Mexican fan palm is one of the most frequently planted palm tree species. It has been planted all over the United States city of Los Angeles and is one of the tallest palm trees on the planet.
I. Appearance and Characteristics
Washingtonia robusta, known by common name as the Mexican fan palm, Mexican washingtonia, or skyduster, is a palm tree native to the Baja California peninsula and a small part of Sonora in northwestern Mexico. Despite its limited native distribution, W. robusta one of the most widely cultivated subtropical palms in the world. It is naturalized in Florida, California, Nevada, Arizona, New Mexico, Hawaii, Texas, parts of the Canary Islands, Spain, Portugal, France, Italy, Malta, Albania, Greece, Turkey, Cyprus, Israel, Palestine, Jordan, Lebanon, Syria, Iraq, Saudi Arabia, Bahrain, Qatar, United Arab Emirates, Oman, Yemen, Iran, Afghanistan, Egypt, Libya, Tunisia, Algeria, Morocco, and Réunion,.
W. robusta grows to 25 m (82 ft) tall, rarely up to 30 m (98 ft). The leaves have a petiole up to 1 m (3 ft 3 in) long, and a palmate fan of leaflets up to 1 meter (3 ft 3 in) long. The petioles are armed with sharp thorns. The inflorescence is up to 3 m (10 ft) long, with numerous small, pale orange-pink flowers. The fruit is a spherical, blue-black drupe, 6–8 mm (1⁄4–5⁄16 in) diameter; it is edible, though thin-fleshed.
It is one of two species in the genus Washingtonia. The other is the close relative Washingtonia filifera, which occupies a more northerly distribution. Compared with W. robusta, W. filifera has a thicker trunk and dull green leaves.
Like the closely related Washingtonia filifera (California fan palm), it is grown as an ornamental tree. Although very similar, the Mexican washingtonia has a narrower trunk (which is typically somewhat wider at the base), and grows slightly faster and taller; it is also somewhat less cold hardy than the California fan palm, hardy to about −8 °C (18 °F).
Field research conducted on W. robusta in its native habitat on the Baja California peninsula concluded that its potential longevity may exceed 500 years. Supporting research by Barry Tomlinson and Brett Huggett states that there is “evidence for extreme longevity of metabolically functioning cells of considerable diversity in palm stems.” Many of the iconic “sky dusters” of Los Angeles that have survived the chainsaws of progress are documented in photography from the 19th century.
II. How to Grow and Care
Sunlight
Like most desert plants, the Mexican fan palm grows best in full sun. It can withstand partial shade, though full sun is ideal. You should plant this tree in a location that receives 6 to 8 hours of sun each day.
Temperature and Humidity
Grown in warm desert regions, it follows that the Mexican fan palm is heat-tolerant. What may be surprising is that these trees are also considered to be cold-weather tolerant palms. They can withstand temperatures down to 20 degrees Fahrenheit. Across all temperature ranges, they prefer moderately humid conditions.
Watering
Water an establishing or transplanted Mexican fan palm enough to keep its soil consistently moist for the first few months. Once the roots have developed well enough, or when dealing with a mature tree, allow the soil around the tree to dry out fully between deep waterings. Cut watering frequency by half in winter.
Soil
Mexican fan palms prefer loamy, sandy soil that is well-draining. They are drought tolerant and do best when the soil is allowed to dry out between waterings. Acidic to neutral pH levels are best. They are tolerant of salty soil, which makes them a viable option for coastal areas.
Fertilizing
These tall palms are very fast growers and appreciate slow-release fertilizer monthly during the growing season. For the best results, choose a high-quality fertilizer specifically formulated for palms. As with other rapid growing plants, potassium deficiency can be an issue, so a palm-specific fertilizer is essential for good health.
Pruning
The large fan-shaped fronds droop and collect around the base of the trees as they age. This creates a large skirt around the palm. Although these begin to fall away with aging, spent fronds should be removed to keep the palm clean and to prevent fire hazard. A professional arborist might be needed if the palm is very large.
Propagation
Unlike other palms, the Mexican fan palm does not produce suckers. This means that to propagate this palm, it must be started from seed. This a great way to multiply your palm trees since they grow well from seed. You will need small pots, moist, well-draining soil, and a heating tray. Then follow these instructions:
- Some seeds require soaking in order to germinate. Check your package for details. If they require soaking, place the seeds in water and let them soak for 24 hours.
- Once the seeds have soaked, plant them in small pots with moist, well-draining soil.
- Place the pots in a warm environment. Setting the pots on top of a heating tray will help keep the seeds warm and encourage germination. This is especially helpful if you do not have a warm environment to start them in.
- Keep the soil moist. Germination should occur in 14 days.
Potting and Repotting
Despite their extremely tall mature size, young Mexican fan palms grow very well in containers. This is a great way to enjoy these palms even if you do not have the space needed for a mature tree. Keep them in sturdy, well-draining containers. Keep in mind that potted palms will need more frequent watering than those planted in the ground, so it is important for water to drain through.
If the palm outgrows the container and you want it to grow larger, you will need to repot it. Tip the pot onto its side and gently tap the pot to loosen the roots. Slide the palm out and plant it into a container that is several inches larger. Fill it with well-draining, fertile soil.
Overwintering
Because these palms grow in areas with warm winters, no extra care is needed to overwinter Mexican fan palms. Simply withhold fertilizer and slow down on watering.
Pests and Diseases
Fortunately, the Mexican fan palm is as tough as they come.
Indoor specimens may suffer from an infestation of mealybugs or whiteflies if they are kept in cramped, poorly lit, or overly humid conditions. Outside, there’s not a lot to be worried about.
Common Pests
Here’s a general overview of some pests you might encounter outdoors:
Palm Leaf Skeletonizer
The larvae of the palm leaf skeletonizer moth (Homaledra sabalella) create large translucent blotches on W. robusta leaves and can cause leaves to die and drop off.
Keep your eyes peeled for the droppings of the caterpillars, which look like teeny black or green balls.
If you find them, wash the leaves vigorously with a strong stream of water from the hose and remove any that remain by hand.
Palm Weevils
Palm weevils in the Rhynchophorus genus can cause major damage to palms.
The adult weevils lay eggs in the crown of the palm and the larvae feed on soft, juicy bud tissue. Because these trees can only produce shoots that grow up, and not laterally, damage to the plant’s sole point of growth is often fatal.
If you manage to catch the infestation early, remove and destroy the insects and/or apply neem oil.
Many other types of palm weevils feed on the crown of these trees, however, none are as destructive as the invasive R. palmarum and R. ferrugineus.
Common Disease
Most of the common issues affecting Mexican fan palms are related to an overabundance of moisture.
Butt Rot
Butt rot is caused by the fungus Ganoderma zonatum, and as it progresses the trunk decays and gradually turns hollow.
Among the first signs of infection are drooping or yellowing leaves. Unfortunately, there is no cure for butt rot.
G. zonatum is commonly found in soils, and sadly, the only way to control this condition is to destroy all diseased plants and avoid planting palms in the same location.
This fungus can affect both indoor and outdoor specimens.
Fusarium wilt
The easiest to identify symptom of this disease, caused by the fungus Fusarium oxysporum, is the rapid death of older leaves.
At first, leaves appear to be affected only on one side of the midrib, but the fungus eventually spreads across the entire leaf, killing it.
Ultimately, this disease will kill the tree. Currently, there is no cure for fusarium wilt and it can affect both indoor and outdoor trees.
Phytophthora Bud Rot
Phytophthora palmivora is a water mold (oomycete) that kills tender, developing tissues in new leaves and buds. The first signs of infestation are discolored, wilting leaves.
This pathogen typically gains a foothold when trees are damaged by cold or physical trauma.
Unfortunately, there is no cure for this disease. Any affected plants and their soil should be destroyed, and not composted, to prevent further spread.
Young specimens are generally more susceptible than those that are well established.
III. Uses and Benefits
If you’re lucky enough to live somewhere where sunshine and warm weather is constant, use one of these quick-growing trees to really make a statement in your garden.
W. robusta is a hardy, unfussy, and all around excellent choice for a landscape tree of epic proportions.
Just bear in mind it will grow tall – very, very tall – and can be toppled more easily than smaller trees in high winds.
If you live in the colder climes but are longing for the warmth of Baja, try this adaptable tree in a pot, either indoors as a houseplant or a patio specimen with winter protection.
