Answer: Mexican fan palms (Washingtonia) is hardy to 20F. If winter temperatures remain above 20F, your palm trees should be just fine. If weather threatens to get colder, the fronds may be damaged. I've heard that wrapping the trunk and fronds with plastic bubble wrap during very cold snaps will help the palm survive (leave the very top open so the tree can breathe). Of course, this only works on small trees! Be sure to remove the wrap when the sun comes out or the tree might overheat.
Best wishes with your palms!
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