Answer: Mediterranean fan palms are among the hardiest of palms, which makes it a good choice for your Seattle area garden. It can be damaged by frost, however, so protection is key to keeping one healthy. It's normal for the lowest (oldest) fronds to die off after 2-3 years, to be replaced by healthy new fronds from the crown of the plant. Frost damage can prematurely turn the fronds brown. Frost can also kill the crown, which will eventually kill the plant. It's a little late in the year for frost damage to be showing up so we'll eliminate that and concentrate on the two other possiblilities. Browning fronds can be the result of over- or under-watering, of fertilizer burn or of a disease called Phytophthora palmivora. This disease also attacks Mexican and California fan palms, Washingtonia robusta and W. filifera respectively, causing bud rot and destruction of young plants. Infected plants exhibit a general decline in plant growth, with the spear leaf becoming pale green then greenish-brown followed by light brown, as leaves become desiccated. The bases of infected leaf stems develop tan-colored necrotic rots with brown margins, and plants are slowly killed as buds are entirely rotted. It is a fungus and once you notice the symptoms, the plant is usually fully involved with no chance of saving it.
Palms in general are easy care plants. They need well-draining soils and adequate water during the growing season. The soil should be allowed to dry out between waterings (difficult in the Pacific Northwest!) and when it is time to water (every 7-9 days), it's best to flood the entire root zone rather than apply a small amount on a daily basis.
Hope this information sheds some light on the possible causes of the problem with your fan palm.
Best wishes with your garden!
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