When Spaniard Hernando Cortez invaded Mexico in 1519, he found dahlias to be a long-established favorite in the gardens of the Aztecs. New World natives, dahlias are a beautiful but tender perennial flower with a fleshy tuber, or underground stem, that looks a lot like a sweet potato. Dahlias provide wonderful cut flowers, with blooms ranging in size from as big as a dinner plate to only an inch across, depending on the variety.
Flowers are showy from mid-summer until autumn.
Some of the low growing varieties can be used as a colorful, inexpensive summer hedge. If the soil's dried out in your flower garden, it's time to start planting dahlia tubers, advised Ross Penhallegon, horticulturist with the Oregon State University Extension Service. The tubers, planted in the spring, are then dug in the fall and stored during the winter in all but the mildest coastal climates. Starts are rooted cuttings taken from a mature dahlia plant. Dahlias from starts will usually die with the first frost in the fall, whereas tubers can be pulled and saved.