California Palm - These palms are native to southern California parts of Arizona and northwest Mexico, growing as high as 90 feet in their native habitat.
California Washingtonia(W. filifera) is hardy to 18° degrees F. it prefers a dry Mediterranean climate, and will not grow taller than 40 to 50 feet in the Pacific NW. They grow in the desserts of Arizona, Mexico and California and like a well drained soil. Intolerance of wet & prolonged cold is the main reason the filifera species cannot grow properly in temperate marine climates. W. robusta (Mexican Fan Palm) is less sensitive to moisture than filifera, but far more tenderer to cold. Growth rate: moderate to fast Hardy to USDA Zone 8A
Note: the Mexican Fan Palm Washingtonia(W. robusta) Mexican Fan Palm is somewhat less hardy and will not with stand the colder winters in most of the Pacific NW .It has anarrower trunk and stiffer leaves than W. filifera, and is hardy to USDA Zone 9A about 20°F How ever the Brookings, Harbor & Gold Beach Oregon areas the Mexican fan palm does quite well.
To plant and grow them west of the Cascade Mountains in the Pacific NW, you will need to make a mixture containing 50% good potting soil, with 25% landscape sand & 25% small pea gravel, (never use beach sand in the soil mix). Have the root ball raised about 1/4 out of the hole but mounded up with the soil mixture. Plant in an area that will get early morning and mid day sun during the winter months. Protect from high off shore winds if planting on the coast.I recommend using a water meter the first few years. In colder areas plant on the South side of a fence or building this will generate radiant heat from the sun in the winter helping to protect the palm on colder nights. (may need some protection on colder winter days)