Virtues: The dahlia flowers from midsummer to fall, with eye-catching blooms that are great for making fresh-cut bouquets.
Common name: Dahlia
Botanical name: Dahlia cultivars
Flowers: Dahlia flowers range from 2 inches to 10 inches in diameter and have a diversity of forms, from simple "single" types to the multipetaled "cactus" varieties (shown above). Colors are equally diverse in the dahlia; they are mostly bright, not pastel.
Habit: Herbaceous perennial. Dahlia cultivars range from 6 inches to 3 feet tall.
Season: Midsummer to fall, for flowers.
Origin: Garden dahlias are bred from species native to Mexico and Central America.
Cultivation: Grow dahlias in full sun, in fertile, well-drained soil. In hot climates the dahlia appreciates some afternoon shade. Plant dahlia tubers outside in spring after all danger of frost has passed. (Here's a trick for starting dahlias earlier in cold climates.) When planting tall dahlias, place the tubers about six inches below ground level and cover them with three inches of soil. Shorter varieties can be planted more shallowly. Be sure that the eye of the tuber is pointing up. Go back and add more soil as the dahlia tubers sprout and grow, until the hole is full. Put stakes in place before the stems get very tall, and tie the stems to the stakes as they grow. Dahlias like regular moisture and a light monthly all-purpose fertilizer. Begin watering only after the dahlia tubers have sprouted. Deadhead dahlias regularly for continued bloom. The dahlia is generally hardy to USDA Zones 8–11. In colder climates, treat the dahlia as an annual, or the tubers can be dug up and stored after the foliage is killed by fall frosts. Illustrated instructions are included in Horticulture's "Fall Tasks" download.
Order Horticulture's Bulbs CD, which includes searchable articles on bulbs and tubers for spring, summer and fall flowers.
Grow a garden for butterflies with Renee's Garden "Seeds for a Butterfly Garden" pack—it includes three easy-to-grow annuals: zinnias, cosmos and sunflowers, to sow outside after the last frost.