Umar bhai, absolutely right. I have never depended on dehlia tubers in the hotter areas. Cuttings do the best and is a far easier method than attempting to save the tubers.
rafique bhai, these dahlias are planted in full sun. To get a bigger bloom, soil preparation is very important. During march, I do not let the small plants grow at their own and keep cutting the tops with a sharp scissors. Initial buds are also plucked and the plant is not allowed to flower. It becomes a compact, healthy and bushy plant by end march. And than by second week april, it is set free. Now after a while I will again cut them to 6-8 inches height. This will reduce the surface area and the plant will be able to survive Okara heat better though it won't be easy. In the meanwhile, many cuttings have already been planted in the shade so even if I loose them in heat, new plants would be available. In monsoon, good drainage is to be ensured.
regards