Native to mountainous central Mexico, dahlias grow well in sunny locations with well-drained soil. Poorly drained soil may lead to disease or even rotting dahlia tubers. Dahlias range in size from ½-inch pompoms to 12-inch or larger flowers on plants that reach several feet tall. They exist in single, double and intermediate forms and come in nearly every color except true blue. Stakes or cages are helpful in supporting dahlias and their potentially heavy flowers during wind and rainstorms. Start dahlias indoors, and place stakes in the ground before you plant the dahlias outdoors.
Start dahlias indoors six to eight weeks before the last frost in your area. Fill flowerpots half-full of moistened potting mix. Set a dahlia tuber in each pot horizontally on top of the potting mix.
Cover each tuber with 1 to 2 inches of potting mix. Leave the crown sticking out. Water until the soil is thoroughly moistened. Place planted dahlia tubers in a shaded location where the temperature is between 70 and 80 degrees F.
Keep the potted dahlias moist. When shoots emerge, place the pots in a sunny window.
Transplant the dahlias into the garden after the danger of frost has passed. Or move them outside, leaving them in their pots.