Large palm, native to the mild areas of North America; to the genus Washingtonia also belongs the robust species, very similar to the filifera, a little less resistant to cold and with greater water requirements. The washingtonia filifera or palma della california develops a fairly thin stem, slightly enlarged at the base, which can reach 15-20 meters in height; the fronds are arched, with a long rigid petiole, up to 200-250 cm long, dark green, the foliage, at the apex of the long petiole, constitutes a wide rounded fan, consisting of pointed, ribbon-shaped segments, which are joined in the lower part, up to two thirds of their length. As with other palms, even in the case of washingtonies, the fronds are evergreen, and last on the plant for several months, before drying up. One of the distinctive features of the washingtonia lies in the fact that the dried fronds remain long on the plant, before falling; in fact, the foliage shows a good number of completely dry, straw-colored fronds in the lower part. During the summer months it produces long clusters of yellowish flowers, followed by small dark fruits, which contain the seeds.
These palms prefer very sunny, even direct, positions, although they can tolerate places with a few hours of light shade per day; they do not fear the cold, and can withstand very intense frosts, for periods not too long. As for the wind, the California palms can be damaged by too strong and cold gusts. This particularly concerns the youngest plants that will need a support or a guardian to grow at their best in those areas where the wind is regularly present.
For a good resistance of the species it is very important that during the winter period it does not receive watering of any kind; for this reason it is not widely used in coastal areas.
It is advisable to water the young plants of washingtonia filifera in the event of prolonged drought, during the hottest months of the year; during the cold months the watering must be suspended completely as the Washingtonia filifera does not need any type of irrigation but rainwater will be sufficient for their growth and development. In fact, the adult specimens are satisfied with the rains and can survive for months even without water. It is the rest of a plant of warm climates that has one of its main survival skills in the excellent use of water resources. When watering during the particularly hot or dry months, remember to avoid excesses and to wet the soil deeply.
The palms of California prefer medium rich, and above all very well drained soils; avoid damp and very heavy soils because the plant may experience problems during growth. When planting these plants it is advisable to work the soil well, mixing a good quantity of sand or pumice stone in such a way as to guarantee the plant of California the ideal soil for its development.
As for the fertilization, this must take place in spring or autumn. We will use humus or mature manure to be placed in the soil near the stem of the plant. During the spring season, to avoid the attack of parasites and the consequent development of diseases, it is advisable to perform an insecticide treatment in such a way as to prevent the problem and thus avoid the appearance of fungal diseases and the onset of parasites.
These palms propagate using the seeds contained within the fruits; sowing will be more successful the fresher the fruits from which the seeds are extracted; it is advisable to keep the soil of the seedbed quite humid, until the young seedlings have begun to develop and the foliage.
The multiplication of the species is carried out especially to create public trees in coastal areas or in private gardens. Thanks to the beauty of the Washingtonia filifera and its rusticity, it is chosen among numerous other species also to create evocative and characteristic avenues, especially in the Mediterranean areas and in the Po valley.
California palm - Washingtonia filifera: Pests and diseases
Usually the palms are ruined only by late frosts, which conspicuously stain the foliage, or by particularly rainy winters, which can cause radical rot.
Another problem that these palms may manifest is the attack of the red weevil. These are larvae that manage to penetrate the trunk of the plant by digging deep tunnels inside it, weakening it and bringing it, in the most serious cases, to death. Often this larva causes the death of entire families of palms causing their extinction.
Today, to address the problem a decree was issued in our country with the aim of reducing this problem. Anyone who notices the presence of this insect is required to take action by alerting the person in charge so that they can undertake a solution and end the problem once and for all.