Dahlia blooming, long roots but no tuber formed?

[Chipandcookie]

Hi everyone, I bought some nice blooming dahlias at the nursery yesterday. When I was transplanting them I realized that there was no tuber formed at all. The roots are very long and dont look like dahlia roots to me.
I need to store them in the garage over the winter becasue they are so pretty I don't want them to die. Is there anyway to form the tubes?

 

[Mike Allen]

Give them time. Gradually the roots will basically swell and begin to resemble what we recognize as tubers. As the season ages and eventually the plants tend to die back, the tubers will develope and to simplyfy, the receding nourishment will be stored in the tubers. So when the plants begin to shut down / die back, just like spring bulbs. Let nature take it's course so that the tubers/bulbs are full of goodies.
In general practice. I avoid being too cosmetic with plants, and let the first of the frosts tell me when to cut down.