Dahlias will grow in nearly any soil as long as you have 12-14 inches of tillable depth. Sunlight is important to dahlia growth and flower production. Your dahlias should receive a minimum of 8-10 hours of direct or slightly filtered light. Plant them in a bright spot. Deep shade promotes lanky growth and few blooms.
Dahlias do very well when grown in large pots or garden boxes. This is a good strategy if you have limited space and want to use dahlias as patio decorations. They are heavy feeders and will benefit from additional fertilizer. They also do best if the foliage is kept dry. Wet blooms are prone to disease and can cause plants to topple. If your plants appear to be wilting, increase the water frequency. Afternoon wilting on extremely hot days is natural, as long as the plants appear to recover in the evening after the temperature has gone down.