I was wondering why my little Potentilla was growing so much suddenly. Then I picked the pot up and found this, the pot is stood on some soil to help keep moist and I have not moved it for a while. I will leave it now as it is doing well.
It is also used to grow very small mame-bonsai in Japan this way. I have seen them at nurseries standing on a plastic grass mat with water at the bottom, growing their roots through the bottom of the pots to reach the water underneath. Growing more healthy this way. Also double potting is an option.