Dahlias can be planted outdoors after the last frost in your area. In central Iowa, dahlias can be planted around May 10 to 15. Gardeners in southern Iowa can plant a few days earlier. Wait several additional days in northern areas. A frost or freeze can damage or destroy the plants.
Dahlias perform best in full sun and a well-drained soil.
Avoid wet poorly drained soils as tubers may rot. Tubers radiate out from the dahlia crown like the spokes of a wagon wheel. Viable tubers must have an eye originating from the crown portion, plus a neck that connects the crown to the body of the tuberous root. Before planting, drive a support, such as a metal fence post stake, wooden stake, or other device into the ground. Placing the supports into the ground prior to planting ensures that the tubers will not be impaled.