I've tried to kill potted plants (1gal) by putting them outside during sub-freezing weather. I live in the Sierra Nevada foothills in California, and while our cold temps don't normally hit as low as many areas, we see plenty of sub-freezing weather. I couldn't kill those plants! Put them out in December and left them there until the following June, and those damn things persisted until it got hot and too dry, then they finally died (I didn't have the heart back then to just yank them, I simply left them to die like old people in the forest). In-ground large plants like we have? I've never seen frosty nights do more than cause purpling. A bigger concern of course is mold, especially if the rains hit (which, this year, I'm praying for them, but not expecting them). Adding the straw mulch and having the fencing like you do, I bet they'll do just fine as long as it's not too wet. :) Even having to pull that one plant, I bet you'll do really well this year.
