Do not set young plants or small tuberous roots outdoors until danger of the last frost is past. Tuberous roots should be laid on their sides, with buds facing upward, in holes four to seven inches deep. Cover with about two inches of soil. Use the deeper planting on sandy soils and the shallower one on clay soils. Insert a four to six foot stake into the ground at the edge of the hole before the tuberous roots are planted.
Dahlias are large plants and require support.
The tall cultivars cannot support themselves and plant breakage will occur without support. As growth appears, remove all but the strongest shoot. Soil should be filled in around the plants as they develop until the surface is level. Spacing of the plants depends on the cultivars grown. Use a three foot by four foot spacing for large types and a two foot by three foot interval for small ones.