Dahlias are large flowers that grow from bulblike tubers, much like potatoes. They require warm soil to sprout and eight hours of sunlight a day to thrive. Varieties range from 30 cm (12 inches) tall to 1.8 m (72 inches) with flowers from 5 cm (2 inches) across to 30 cm (12 inches) in diameter. Dahlias come in a range of colour except blue. Some petals are flat, others quilled. Several varieties are multicoloured. It's not difficult to plant them in pots.
Fill the container with fresh potting soil. Don't reuse old potting soil. It may contain the fungus that causes dampening off, which will kill the tuber and sprouts.
Dampen the soil so it's moist but not soggy. If you were planting the dahlia tubers in the garden you wouldn't plant in damp soil, but pots dry out much quicker than the garden, so moist soil will help the tubers get going.
Place the tuber in the middle of the pot, or if you are planting more than one, place them equidistant from each other and the edges of the pot. Plant no more than two tubers in a 60 cm (24 inch) pot.
Cover the tuber with 15 cm (6 inches) of soil. Pat the soil down gently.
Place the pot in its permanent location where it will receive a minimum of eight hours of sunlight.
Water only after the tuber has sprouted. Keep the soil moist but not soggy. Wet soil encourages the tuber to rot. Because dahlias require warm soil and lots of sunlight, the pot may require frequent light watering.
Select low-growing or dwarf dahlias for containers. If you're not sure of the capacity of the pot, note the cubic measurement on the bag of potting soil and determine the capacity from how much of the soil fills the pot. Don't set the pot in a saucer unless you put pot feet under the pot so there is air space between the pot and the saucer.
It's difficult to grow dahlias in hot, dry climates.