Dahlias are perennial plants that grow from tubers, although most gardeners grow them as annual plants. These flowering plants form seeds, but planting them usually results in substandard growth and an appearance that differs from the parent plant. Dahlias are winter hardy in USDA zones 8 and warmer. Lifting and storing the tubers in cooler areas provides a method of shelter during the winter for renewed growth the next spring.
Dahlia variabilis is the scientific name for dahlia plants. These plants come in a variety of cultivars and are 1 to 6 feet tall at maturity. The showy blossoms appear in shades of yellow, white, pink, purple, red and orange. The double and single flower heads make good cut flowers and tend to retain their freshness for more than a week in a vase.
The time that dahlias begin producing blossoms depends on the time of planting. Gardeners in cool climates must wait to plant dahlias outside until after the last frost. Most dahlia cultivars take about two months to form the first flower bud. Pinching out this initial bud encourages the formation of numerous blossoms that begin to open about one month later. The peak season for dahlia blossoms occurs approximately four months after planting. Dahlias continue to bloom until the first killing frost wilts the exposed foliage and blossoms.
Longer Flowering Season
While gardeners in warm climates can enjoy a long flowering season, the length of time for blossoms to appear limits their display in colder climates. By starting the tubers indoors, you can enjoy a longer flowering season. Plant the tubers about six weeks before the final frost. Use 1-gallon pots and loamy potting soil. Plant them to a depth of about 6 inches and place them in a sunny, indoor location. Transplant them into the garden after soil temperatures reach at least 50 degrees Fahrenheit.
Dahlia plants grow readily in a variety of soils, but prefer loose, loamy mediums with even moisture. Pinching out the first flower bud as soon as it forms is an important factor in producing abundant blossoms over the entire plant. Snipping out wilted blossoms enhances the appearance of dahlia plants and encourages continued flowering. Dig the tubers in the fall and store them in a protected location that maintains an even temperature between 35 and 50 degrees Fahrenheit. Divide the dug tubers before replanting them in the spring.