Dahlia spp. Ht. 2′–6′ Spread 2′–4′ Spacing 12 - 24"
HABIT: Colorful flowers from spring to fall. Does not bloom well in the hotter parts of the summer. Dwarf varieties are the best here.
CULTURE: Needs sun, rich porous soil, and heavy amounts of fertilizer. Plant in February or March. Cultivate around plants until blooms form, then mulch heavily.
USES: Summer flowers, background plant for perennial beds, cut flowers.
PROBLEMS: Heat, red spider mites.
NOTES: Dahlia is the national flower of Mexico.
Mid- to late-summer flowering plants that offer more varied flower colors and shapes than most other garden plants (only tulips top dahlias in number of colors). Choose from nearly every color under the sun (except true blue or black), and from flower types as varied in shape and size as cactus, decorative, water lily, pom pom, collarette, peony-like, dinner plate (which are truly that big) and more. In fact, official registries list thousands of named varieties.
Dahlias are tender summer bulbs (tubers, to be exact). They grow quickly and flower profusely, reaching their peak in the sun-dappled months of late summer and autumn.
Native to Mexico, dahlias are sensitive to frost and should not be planted outdoors until the threat of frost has passed. To get a jump on the season, start up tubers indoors in pots in early spring then plant them outdoors when the weather has warmed garden soil to approximately 60º F (or slightly warm to the hand). Appealing selections of bare bulbs and pre-grown nursery plants are available in spring at garden centers, home centers and via mail-order or internet gardening firms.
Dahlias come to flower in July and continue to flower till the hard frosts of fall. The more you cut dahlias, the more flowers they produce.
As tender bulbs, dahlias will not survive exposure to harsh winter weather. At summer's end, either leave the bulbs as you would annuals, compost them, or store them in peat moss in a protected spot over-winter for replanting the following summer.