<em>Washingtonia</em>, skirt palm: to plant, to grow and to 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 the south-west of the United States (California, Arizona) and the north-west of Mexico (Baja California, Sonora). It occurs in arid zones, mainly in gorges and canyons, sometimes close to 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, and therefore belongs to the Arecaceae family, which comprises more than 2,500 species. Palms are impressive, highly structural plants in the garden. Their mere presence brings a strong exotic feel and creates a distinctive atmosphere. They have a characteristic silhouette, with a tall, very straight stipe from which a crown of leaves unfolds at the top, often of considerable span, all attached directly to the stipe by a petiole.

Washingtonia owes its name to the first president of the United States, George Washington (1732–1799). In English this palm is nicknamed sky duster. The specific epithet filifera refers to the long white threads that detach from the tips of the fronds.

Washingtonia grows very quickly. It develops a single, obviously unbranched stipe. It is very tall and straight, vertical, and can reach up to 80 cm in diameter. A palm stipe is made up of the stacked bases of the petioles and cannot really thicken in diameter, only gain height. If the top of the stipe is cut or dies, the entire palm will be lost (unlike other trees and plants that can produce branches). Largest Washingtonias reach up to 20-25 m in height. Washingtonia filifera has a stipe that is stouter, thicker and broader than Washingtonia robusta.

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

Washingtonia bears large, attractive palmate leaves, fan-shaped. They are thick and rigid, with a pleasant light green colour. They form a rounded outline but are cut into numerous plicate leaflets, long and narrow. The leaflets of Washingtonia carry long whitish fibres (fibres that detach from the margin of the leaflets), which gives Washingtonia filifera its species name. Leaves of Washingtonia are borne on long petioles (up to 2 m), which are edged with orange teeth or thorns. Washingtonia robusta has broader, more pronounced and more aggressive thorns than Washingtonia filifera.

When old, leaves dry out and form a sort of skirt around the stipe beneath the still-green leaves. This is how the palm earned its common name of “skirt palm”.

Bases of the petioles of old leaves remain in place for several years, then eventually fall, revealing a smooth brown bark.

Washingtonia flowers in summer, producing large inflorescences that can reach up to 4 m in length in Washingtonia filifera! They emerge among the leaves at the same level and extend well beyond them. They are highly visible and impressive. These are long, pendulous, branched panicles made up of small cream-white flowers. Flowers are cream-white, tending towards pale yellow or pale pink. They 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 the ground. Likewise, a plant must reach adult size before flowering; younger palms do not flower.

After flowering, Washingtonia produces numerous small rounded fruits, which replace the flowers. These are drupes, brown to black in colour, measuring between 0.5 and 1 cm in diameter. Each fruit contains a single seed. A single Washingtonia plant is sufficient to produce viable seeds. Fruits are edible and were used by Native Americans. They are also enjoyed by birds, which disperse the seeds after digesting the 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 hardy than Washingtonia robusta, able to tolerate 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 resembling W. filifera, but with a thinner, more graceful stipe and slightly shorter petioles and inflorescences. It is also appreciated 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 in full sun, in a location sheltered from cold winds. It will be happy in a free-draining soil that does not retain too much moisture in winter. Washingtonia also prefers soils rich in organic matter, fertile. Do not hesitate to add well-rotted compost from time to time. Likewise, Washingtonia prefers slightly calcareous soil.

Washingtonia is a large palm, with leaves and inflorescences that take up space: allow enough room for it to develop properly. Avoid, for example, planting it too 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 back out in spring when temperatures become milder. You can then place it on your terrace or in an inner courtyard, preferably in sun.

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

Washingtonia palms make magnificent avenue trees, for example when 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 will be able to make the most of summer to get off to a good start before facing colder winter temperatures.

How to plant?

For planting in open ground:

1. Start by digging a large planting hole, which should be two to three times the volume of the rootball.
2. Place soil at the bottom, mixed with a little well-rotted compost and, if necessary, 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 digging slightly around the stipe, to retain watering water and help it infiltrate at the base of the palm.
5. Water generously.

Continue to water in the weeks that follow, 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 pots, clay balls or gravel. It will prevent water from stagnating at the bottom of the pot.
3. Add potting compost mixed with garden soil and coarse sand.
4. Plant your palm.
5. Replace soil around and firm down gently.
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, give a few waterings in spring and summer during the first years. If grown in a pot, waterings should be more frequent, as the potting compost tends to dry out quickly. Water mainly during the growth period, but reduce watering in autumn and winter.

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

If you grow Washingtonia in a pot, remember to bring it indoors in autumn to place it in a bright, frost-free shelter, then take it back out in spring. Acclimatise them gradually (especially when young!): avoid placing them directly in full sun, but initially put them out temporarily in semi-shade, bringing them in at night before placing them outside permanently. Also remember to repot, on average every two years, preferably in spring. If you grow it 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 horticultural fleece, and applying a thick mulch at their base. They will become more cold-hardy as they age.

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 tunnels and consumes palm stipe. New leaves that appear are deformed, perforated and dry out. You may also observe sawdust, cocoons, gallery holes, with viscous gum at entrance. You can spray a nematode-based solution that parasitises these larvae. Also do not hesitate to call in a professional.

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

You may also encounter problems with red palm weevil, Rhynchophorus ferrugineus. It is a beetle native to Asia, red and black in colour, about 3 cm long. It attacks heart of palm, causing central fronds to fall. Crown of leaves becomes bare and collapses. If left untreated, palm may die. Nematodes or a pathogenous fungus (Beauveria bassiana) can be used against the weevil. If you have other palms, protect them to prevent 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, 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 plants of Washingtonia by sowing seeds. Sowing takes place in spring.

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

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

Association

Washingtonia is an imposing palm; its mere presence is ideal for recreating an exotic, lush atmosphere. Plant alongside it other plants with generous, very green, well‑developed foliage. Choose, for example, arborescent ferns, other palm trees, Tetrapanax, Persicaria polymorpha, bamboos… You can also include a few climbing plants, such as Akebia quinata, bignonias or passionflowers. At pond edges, 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, lavender, cistus, phormium, yuccas and opuntias… Also make use of Senecio cineraria, valued for its elegant, finely divided silvery foliage. If you wish to include a few trees, consider mimosa or Lagerstroemia. For hedge or specimen planting, include oleander, Nerium oleander, admired for both foliage and generous flowering.

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