Dig an area twice the size of the pot you are going to put in it. Incorporate some compost or well rotted manure or other form of fibrous material to help the soil hold water. Give the back filling mixture a small handful of blood fish and bone or other fertiliser, and mix well in. Plant and remember to give it plenty of water. Smaller dahlias don't need a stake, but larger ones will. It should then flower until the first frosts so long as you remember to deadhead it.
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First flower!
If you have to behave like a twat, at least learn English Grammar first.