It's time to wrap your borderline plants or perhaps - kiss them goodbye. When temperatures drop into the low 20's (It was 23 degrees on my deck in Langley early this morning) night after night, the sustained chill damages and kills off plants like melianthus, ceanothus, hebes, phormium, fan palms, big-leafed rhodies...don't even get me started on all those marginal beauties from New Zealand and Australia.
Of course, it depend on the microclimate where you live, on wind-chill, if you've already mulched well to protect your plants.
But I lost an entire, established hedge of escallonia years ago in a deep freeze that lasted an entire week - sunny days get the plants juices flowing, then a precipitous drop in temperatures, night after night, finished the plants off.
Our forecast is a similar scenario. Friday night in Seattle is supposed to drop to 19 degrees! And not to rise above freezing at night until next Tuesday. You can drape old bath towels around the base of your plants, wrap them in bubble wrap...or start dreaming of what you'll replace them with come spring....
My poor, potted big-leaf rhodie was not happy this morning....it's folding its leaves down to protect itself from what's to come (predicted 21 degrees in Langley by tomorrow night...).