Dahlias flower mainly in late summer and autumn, so there's no need to be in any hurry to plant the tubers out. They won't start into growth until the soil is far warmer than at present. I assume you are talking about tubers? In which case getting them to sprout under a little heat, shallowly buried in compost, would enable you to take cuttings from the new shoots, all of which will produce a new plant. Just carefully cut off the new shoots as close as you can to the tuber and pot them into a very gritty compost or one with perlite or vemiculite, contained in a polythene bag to stop the leaves wilting. They root after a couple of weeks.
If you are talking about seed, then sow in late April or May. They will make good plants which can be lifted in the autumn and the tubers stored in the usual way.