<em>Washingtonia</em>, Mexican fan palm: plant, grow and care for

Description and botany

Washingtonia, also called Skirt palm, is a large palm with an imposing stipe and palmate foliage. It is native to south-west United States (California, Arizona) and north-west Mexico (Baja California, Sonora). It occurs in arid areas, mainly in gorges and canyons, sometimes near watercourses. Only two species exist: Washingtonia filifera and Washingtonia robusta, which can be easily confused. There is also a hybrid between these two species, Washingtonia x filibusta.

Washingtonia is a palm, therefore part of family Arecaceae, which includes more than 2,500 species. Palms are impressive, highly structural plants in garden. Their presence brings a strong exotic feel and creates a particular atmosphere. They have a characteristic silhouette, with a tall, very straight stipe from which, at the top, a crown of leaves unfolds, often of large span, all attached directly to stipe by a petiole.

Washingtonia is named after first president of United States, George Washington (1732–1799). In English this palm is nicknamed Sky duster (“plumeau du ciel”). Species name filifera refers to long white threads that detach from tips of fronds.

Washingtonia grows very quickly. It forms a single, obviously unbranched stipe. It is very tall and straight, vertical, and may reach up to 80 cm in diameter. Palm stipes are formed by stacking bases of petioles and cannot really increase in diameter, but only in height. If crown of stipe is cut or dies, whole palm will be lost (unlike other trees and plants that can branch). Largest Washingtonias reach up to 20–25 m in height. Washingtonia filifera has a stipe stockier, thicker and wider than Washingtonia robusta.

Stipe of a Washingtonia filifera (photo F. D. Richards), its leaves (photo Marija Gajić), and thorns covering petiole of a Washingtonia robusta (photo Forest and Kim Starr)

Washingtonia has large, attractive palmate leaves. They are thick and stiff, with a lovely pale green colour. They form a rounded outline but are divided into numerous plicate, long fine leaflets. Leaflets of Washingtonia bear long whitish threads (fibres that detach from leaflet margins), which gives species name to Washingtonia filifera. Leaves are borne on long petioles (up to 2 m), which are fringed with teeth or orange thorns. Washingtonia robusta has broader, more pronounced and more aggressive thorns than Washingtonia filifera.

When old, leaves dry and form a kind of skirt around stipe beneath still-green leaves. This is why this palm is commonly called Skirt palm.

Bases of petioles of old leaves remain in place for several years, then finally fall away, leaving smooth brown bark.

Washingtonia flowers in summer, producing large inflorescences that can measure up to 4 m in length in Washingtonia filifera! They appear among leaves at same level and extend well beyond them. They are highly visible and impressive: long, pendulous, branched panicles composed of small cream-white flowers. Flowers are cream-white, tending to pale yellow or light pink, and measure up to 1 cm in diameter. Flowers are tubular and consist of three petals, three sepals, six stamens and a style. Indeed, Washingtonia flowers are hermaphrodite: they bear both male organs (stamens) and female organs (pistil). Generally Washingtonia does not flower when grown indoors, only when planted in ground. Likewise, plant must reach adult size; younger palms do not flower.

After flowering, Washingtonia bears numerous small rounded fruits, which replace the flowers. These are drupes, brown–black, measuring between 0.5 and 1 cm in diameter. Each fruit contains a single seed. A single Washingtonia plant can produce viable seeds. Fruits are edible and were used by Native Americans. They are also eaten by birds, which enable seed dispersal after digesting fruits.

Impressive flowering of Washingtonia, in panicles of cream-white flowers, and its fruits (photo Filo gèn’)

Main varieties

Washingtonia filifera - California Fan Palm

Washingtonia filifera is a superb palm, with a fairly thick, imposing stipe and palmate leaves, deeply divided into fine, elongated leaflets. It is slightly hardier than Washingtonia robusta, able to withstand down to −10 °C in dry soil.

• Flowering time August, September
• Height at maturity 17 m

See the product sheet

Washingtonia robusta - Mexican Fan Palm

Washingtonia robusta is a handsome palm similar to W. filifera, but has a finer, more slender stipe, with slightly shorter petioles and inflorescences. It is also valued for its superb palmate foliage. Less hardy than W. filifera, it nevertheless tolerates down to −5 °C.

• Flowering time August, September
• Height at maturity 24 m

See the product sheet

Planting Washingtonia

Where to plant?

Washingtonia needs warmth: plant it in full sun, in a spot sheltered from cold winds. It will thrive in free-draining soil that does not retain too much moisture in winter. Washingtonia also favours soils rich in organic matter, fertile. Do not hesitate to add well-rotted compost from time to time. Likewise, Washingtonia prefers slightly calcareous ground.

Washingtonia is a large palm, with leaves and inflorescences that become expansive: allow enough room for it to develop properly. Avoid, for example, planting it very close to a building.

You can also grow it in a large container. This will allow you to bring it indoors in winter to protect it from cold, then take it out again in spring when temperatures become milder. You can then place it on your terrace or in an inner courtyard, preferably in the sun.

It is also possible to grow Washingtonia under a greenhouse or conservatory all year round. In that case, place it in a well-lit spot, preferably without direct sun during the hottest hours.

Washingtonia are magnificent as lining trees, for example planted along a path.

When to plant?

Best time to plant Washingtonia is spring, in May or June. Temperatures become milder, which will improve establishment, and it can make the most of summer to begin growth before facing colder winter temperatures.

How to plant?

For planting in the ground:

1. Start by digging a large planting hole measuring two to three times the volume of the rootball.
2. Place some soil at the bottom, mixed with a little well-rotted compost and possibly draining materials: coarse sand, gravel…
3. Plant your palm. Its collar should be at the same level as when it was in the pot. Take care not to bury it, which could cause it to rot.
4. You can create a watering basin by slightly digging around the stipe to retain irrigation water and help it infiltrate at the base of the palm.
5. Water generously.

Continue watering in the following weeks until the palm is well established.

For planting in a pot:

1. Choose a large pot or container. It must have drainage holes in the bottom to allow water to escape.
2. Place a drainage layer at the bottom, made of broken pot shards, clay pebbles or gravel. This will prevent water from stagnating at the bottom of the pot.
3. Refill with potting compost mixed with garden soil and coarse sand.
4. Plant your palm.
5. Replace soil all around and firm lightly.
6. Water generously.

Place the pot in a sunny spot, sheltered from cold winds.

Washingtonia robusta (photo A. Bayer Tamayo)

Care

If you grow Washingtonia in open ground, carry out a few waterings in spring and summer during the first years. If grown in a pot, waterings will need to be more frequent, because the substrate tends to dry out quickly. Water mainly during the growth period, but reduce waterings in autumn and winter.

Older leaves of Washingtonia gradually dry out and remain attached against the stipe, beneath the crown of green leaves. You can choose to cut away this skirt of dried leaves for aesthetic reasons, but we advise leaving it in place.

If you grow Washingtonia in pots, bring them indoors in autumn to place in a frost-free, well-lit shelter, then take them out again in spring. Remember to acclimatise them gradually (especially when young!): avoid placing them directly in full sun, but put them out temporarily in partial shade at first, bringing them in at night before finally leaving them outdoors. Also remember to repot them, on average every two years and preferably in spring. If you grow them in a pot, you can apply liquid fertiliser.

In winter, during the first years, we recommend protecting your palms from cold by wrapping them in several layers of winter fleece, and by applying a thick mulch at their base. They will become more resistant to cold as they get older.

Diseases and parasitic pests of Washingtonia

Washingtonias are sometimes attacked by the palm moth, Paysandisia archon. Larva of this lepidopteran native to South America bores galleries and consumes the palm trunk. New leaves that emerge are deformed, perforated and dry out. You may also find sawdust, cocoons, gallery holes, with viscous gum at the entrance. You can spray a nematode-based solution that parasitises these larvae. Don’t hesitate to call in a professional.

For more information, see our article: “Palm moth, Paysandisia archon: control and treatment”

You may also encounter problems with the red palm weevil, Rhynchophorus ferrugineus. This is a beetle native to Asia, red and black in colour, and about 3 cm long. It attacks the heart of the palm, causing central fronds to fall. Crown becomes bare and droops. If left untreated, palm may die. Nematodes or a pathogenous fungus (Beauveria bassiana) may be used to attack the weevil. If you have other palms, remember to protect them to prevent the weevil or palm moth attacking them.

Palm moth (photo Daniel Villafruela) and red palm weevil (photo Katja Schulz)

When grown indoors, Washingtonias can be attacked by scale insects. In that case, you can use black soap to get rid of them. They may also be targeted by red spider mites, tiny mites that pierce foliage and extract sap. Mist your palm, as red spider mites dislike humidity.

Propagation by sowing

You can obtain new young Washingtonia plants by sowing seeds. Sowing is done in spring.

1. Start by soaking seeds in hot water for 24 hours.
2. Prepare a pot with potting compost mixed with some coarse sand.
3. Remove seeds from water and sow them.
4. Cover with a thin layer of substrate.
5. Water gently.
6. Place pot at about 25 °C in a bright spot out of direct sunlight.

Germination of Washingtonia is fairly rapid (in 1 to 2 months, or even less when seeds are still fresh), compared with other palms. As soon as seedlings are large enough, you can repot them into individual pots.

Association

Washingtonia is an imposing palm; its mere presence is ideal to recreate an exotic, luxuriant atmosphere. Plant alongside it other specimens with generous, lush foliage. Choose, for example, tree ferns, other palms, Tetrapanax, Persicaria polymorpha, bamboos… You can also add some climbers, such as Akebia quinata, bignonias or passionflowers. At pond edge, consider Gunneras and osmundas.

You can also use Washingtonia to create a Mediterranean-style garden with plants adapted to drought and full sun. Choose, for example, santolinas, lavenders, cistuses, phormium, Yuccas and Opuntias… Also take advantage of Senecio cineraria, prized for its elegant, silver-cut foliage. If you want to include a few trees, consider Mimosa or Lagerstroemia. In hedge or as specimen, you can include oleander, Nerium oleander, admired both for foliage and generous flowering.

Washingtonia fits easily into a Mediterranean-style garden! From left to right: Opuntia microdasys (photo Stan Shebs), Helianthemum ‘Ben Fhada’, Washingtonia robusta (photo Alejandro Bayer Tamayo), Nerium oleander (photo Challiyan), and Agave mediopicta ‘Lutea’

Finally, Washingtonia easily finds a place in a modern, graphic-style garden. Plant it in a large designer pot on terrace or in a patio. It will pair beautifully with agapanthus, grasses, Alliums, Eremurus, Ophiopogon, ferns… Include structural plants that draw the eye and add height. Play with lines by introducing verticality and laying out very straight paths to contrast with curved shapes. Stick to very sober colours: purple, chocolate, black, white… The result is a timeless effect, a garden both chic and timeless.