Hi Flowerlover,
Pretty sure you don't have to worry about wind chill. I went through that a year or two ago and decided it was only what it felt like on your skin, and shouldn't bother the plants.
As far as actual temps, we've been down to -16 so far this year and crossing my fingers that they make it through the winter. - Hoping they do, if they can get through this one I think they're pretty hardy! -- Course they've still got to get through the freezing and thawing in the spring... but so far haven't lost an established plant yet.
Lots of gorgeous plants out there.. and if you keep an eye out, you can buy some of them reasonable.
