Root cuttings.

B&Bs have tubers. Cut them back leaving a couple of inches of stems (the new growth will come at the base of the old stems) and dig up the tubers carefully. Rinse them off, let them dry for a few days and put them in a paper bag. Store them in a cool dark place. Pot up in April and transplant when your weather is good. I did this last year in z6b and it worked brilliantly.

Or you could just move them to a cool, dark place in the containers. Withhold all water until you want dormancy to break.

Thank you both. I think I'll dig them up from the large containers, pot them up and place them in our crawl space. Wish me luck! :-)

Having had 'Argentine Sky' for quite a number of years, and only having accquired 'Black and Blue' last year, I understand your desire to keep it, it's so striking. Glad it's hardy here (z7).

They are stunning! I saw another variety that's new to me called, "Indigo Spires". I think that's the name! They had a huge planting at the Chicago Botanic Garden. The plants were at least 3 feet tall. I've never seen anything like it before. Definitely adding it to my 2018 plant list...keeps growing!

As I recall Indigo Spires is salvia farinacea. A worthy plant, but best treated as annual, even where it can be hardy.