You can leave in ground but you run risk of tubers being damaged by frost , better to wait to first frosts in November dig them up store somewhere dry remove most of dirt around tubers . I put them in pots of compost in mid February in a warm room give a good water plant out end of May
I had a lovely orange dahlia in a pot. I moved house and brought the pot with me. I admit I haven't looked after it and now for the last 2 years it hasn't flowered. Lovely leaves. Have recently transferred it to the garden. Will it flower again? If so how can I revive it to flower again.? Still growing lovely leaves.