Hardiness figures are approximate and often based on speculation. They are meant to apply to plants growing in Washington's wet winters and cool summers. 9 F Chamaerops humilis var. F Trachycarpus var. Others will certainly grow in a sheltered spot though they have not been adequately tested here.
Familiarity is still a factor.
Some, however, may indeed be fully hardy here and are not included on either of the above lists simply because they are largely unknown or have not been tested here. Archontophoenix maxima , high elev. Calamus acanthospathus, muelleri, other sp. I have begun working on a web page about palms but it does not look like I will finish for quite some time to come. This is such a broad subject, I am going to have trouble narrowing it down, so I guess my main purpose here will be give a quick taste of what I am growing and what I am interested in, rather than going into a whole lot of detail about each.