Dahlias are a beautiful addition to any garden, but also make nice container plants. They bloom in a variety of colors and sizes, depending on variety. Dahlias have tuber roots that are most commonly divided and replanted for propagation. However, you can plant dahlias from seeds, but plant more than you desire since many may not thrive.
Select a potting soil that contains both peat and vermiculite. In a planting tray, sow dahlia seeds about a half an inch into the soil. Cover the seeds with more soil. Water the seeds until the soil is evenly moist and cover the tray with clear plastic or glass.
Keep the tray in a warm area (70-80 degrees F), but out of the sun until after germination, which usually occurs in 5 to 7 days and at which time, take the cover off. Allow the dahlias to grow and become stable plants until replanting in individual containers, as described below.
Use the same kind of potting soil as described in step 1 to plant dahlia tubers or plants. These can be purchased tubers, tubers that were cut from a larger tuber or the plants you grow from seeds. Be sure the container has holes for good drainage and is at least 12 inches deep and wide.
Plant the tuber so that the bud--also called an eye--is pointing up and is just below the soil's surface (1/2 inch to 1 inch).
Keep dahlias evenly water and in an area that receives approximately 5-6 hours of sunlight. If you place the container outside, once the plant reaches 3-6 inches high, spray insecticide (which kills most pests) and miticide (mite killer) on its leaves every week.
Use a stake if necessary to keep your dahlias stable as they grow larger. Loosely tie the dahlia to the stake once you notice it needs support to continue growing.