Dahlias not growing

Vivien

i bought six Dahlias last year, all in pots. I over wintered them and then repotted in fresh compost in the Spring but while three of them are already nearly two foot high the other three aren't showing any signs of growth whatsoever. I dug one up today to see if the tubers were still healthy and they looked absolutely fine. What's going on?

Hostafan1

It's got little white fibrous roots so it's ,technically, growing . I'd repot and wait