This is a rarer tree Dahlia that I find in many ways better suited to my garden and climate that the common D. imperialis.
For a start it is usually slightly smaller topping out at about 3.5 metres tall with smaller and more interesting leaves. The flowers are a richer mauve and with a flatter daisy form but best of all in cool to cold climates I find that it flowers several weeks earlier so that I normally get flowers before the frost knocks it to the ground.
Like the better known species plant it in a sunny spot with a bit of shelter from the strong winds and stand back!
I have plants in 25cm. pots at the moment for $24.50