Good for cut flowers
Select a site with full sun to light shade and well-drained soil. Tall and large-flowered varieties should be sheltered from strong winds. Dahlias adapt well to growing in containers.
Plant dahlia tubers in spring after all danger of frost has passed and the soil has warmed. Prepare the garden bed by using a garden fork or tiller to loosen the soil to a depth of 12 to 15 inches, then mix in a 2- to 4-inch layer of compost. Dig a hole about three times as deep as the diameter of the tuber, usually between 3 and 8 inches. Set the tuber horizontally in the hole with the buds facing up, cover it with soil, and press firmly. Space tubers 1 to 3 feet apart, depending on the variety, and water thoroughly. Stake tall varieties at planting time, being careful not to damage tubers when installing stakes.
Apply a 2- to 4-inch layer of mulch around dahlias to retain moisture and control weeds. To reduce the height of tall-growing varieties, pinch back shoots when the plant is about 1 foot tall. Dahlias prefer consistently moist soil, so water plants during the summer if rainfall is less than 1 inch per week, and water container-grown plants frequently to keep soil moist but not saturated. Remove flowers as they fade. In autumn, after frost kills the foliage, cut plants back to the a few inches in height. Wait a few weeks so tubers can cure, then carefully lift clumps, brush off any clinging soil, and put them in a plastic-lined box filled with perlite or peat moss, spacing them so that none are touching. Store boxes off the floor in a dry area at 45 to 55 degrees F. Replant in the spring, dividing large clumps into sections each containing one or more buds, which appear as small bumps.