Questions about chocolate cosmos

I lost mine in the past , it didn't come back, although it says zones 6 to 9 so I thought I was safe but not. I just wanted to know how fast they multiply, or do they multiply, I also heard you can dig them up like dahlias and store them in the garage? or perhaps greenhouse? is this true?

I thought i'd try them again this spring.

kathy

Plant Files only lists it as hardy to zone 8, that could be why they didn't make it for you. I haven't grown them so I can't be any help on the rest of your questions.