Pot them into 6 or 8 inch pots, with the crown at least 2 inches under the
compost, Stand them outside, and just bring them in if there is any chance
of frost.
You could "Stop" them when you have 3 or 4 pairs of leaves on the stems,
this will give you a better plant and more flowers.
for more info see http://www.dahlia-nds.co.uk/web2d.htm
and do use slug pellets.......I had a customer who planted out 16 plants,
forgot to put down slug pellets and lost the lot the first night.
--
David Hill
Abacus Nurseries
www.abacus-nurseries.co.uk