What dahlias need
Set tubers in the ground when the soil has warmed to about 60°.
Planting: Plant in full sun (afternoon shade in hot climates) and well-drained soil; mix in organic matter. Dig holes 1 foot deep and 1 to 1½ feet wide, and space tubers 1 to 5 feet apart, depending on plant size.
Lay tubers horizontally with growth buds facing up; cover with several inches of soil and water only if the soil is dry. Gradually fill in the hole as shoots grow.
Fertilizing: Mix ¼ cup low-nitrogen fertilizer into the bottom of the planting hole.
Watering: Once shoots appear, water regularly.
Pinching: Snip off growing tips when plants have their third set of leaves.
Winter care: In wet or cold climates, dig up tubers in fall.