Well done, and guess what? I am originally from your "neck of the woods" - grew up in Vancouver, BC. It always amazes me that our winter weather in Florida is quite similar to your summers up there in the Pacific NW except for the shorter days.
Down here in Florida my Cordylines grow like crazy in the hot weather and pretty much go dormant in winter. So your problems might be related to not enough heat to make them break dormancy. If you have them in pots, try moving them around to the warmest spot in your garden - usually the south side of a building that will heat up during the day and keep the plants warm at night. They will (mostly) take some sun even here so your weaker sunlight should be ok for them.
Another trick to keep them warmer would be to always water them with warm water - let the hose warm up in the sun for a while before watering? I know how cold the water from the tap can be up there!
I'd also take them indoors before the nights start to be too chilly -
@50deg. is getting too cold - so you can maybe keep them growing slowly through the winter.
