Dahlias move easily if grown from a tuber. Just dig up the plant with as much of the root ball as possible and place into a gallon or larger pot. Cover with some dirt. When planting in the new location, it will wilt a bit for as long as a week but will grow just fine. It will probably bloom a few weeks later than normal but should do fine otherwise.

I moved mine when they were about that size. They wilted for a few days, but they were okay. Try to keep as much of the root ball as you can, and don't damage the tuber. The main stem near the tuber seemed quite brittle, so be careful of that.

Thank you. My dahlias are always wonderful -- but when I purchase a small potted plant (looking beautiful) - they often wilt, only to return in spring and look great. I was afraid of the same reaction from a move..