Dahlias

Do you store your Dahlia tubers out of the frost or leave them in the ground?

Mine haven't been removed from the ground for at least 3 years.  Not only do they survive without lifting but have self sown themselves all over.  There is always something which will come up to give a show, even when I have as good as abandoned the borders.  

I've been looking out for the turning of the leaves but there's not much colour in the trees as yet, but the oranges from these beauties is absolutely in tune with the season.