No-Fail Tips for Planting Dahlias
Follow these expert tips and learn how to grow dahlias up to a foot across.
When Kathy Whitfield took her mother to the mall in the fall of 1997, she had no idea that outing would change her life. The pair stumbled upon a sea of blooms in myriad shapes, sizes, and colors set up by the local dahlia society for its annual show. "I didn't know what a dahlia was," Kathy admits. "The flowers were so perfect—they didn't look real." People behind a nearby table invited visitors to join the dahlia society. She recalls, "My mother said, "You go join." And in the South, you do what your mama says."
A few months later, a letter arrived at the Whitfields' mailbox in Hoover, Alabama. Kathy retrieved it and told her husband, "Ed, I think I've joined something." Ed looked at the letter and announced, "I know what dahlias are! My grandmother grew them." The die was cast. Today, the Whitfields grow 550 dahlias of more than 75 kinds in their backyard.
For the uninitiated, dahlias are tender perennials that grow from tuberous roots. You have to dig up and store them over winter in the Upper and Middle South (USDA Zones 6 and 7), but they can stay in the ground year-round south of there. Dahlia fanciers divide them into many classes based on flower form. Blooms come in all colors except true blue, range from 2 to 12 inches wide, and are great for cutting. Plants grow 1 to 7 feet tall.
Anyone who grows more than 500 dahlias every year has our respect. We asked Kathy for her best tricks to help you get started on your first 100.
Beat the Heat
Dahlias dislike long, hot summers, making them challenging to grow in the Lower South (Zone 8), where Kathy lives, and not recommended for the Coastal and Tropical South (Zones 9 and 10). They wilt in hot sun and often stop blooming when the mercury tops 90 degrees. Big-flowered kinds are the most heat sensitive. Kathy addresses this by shielding them in summer beneath 50% polyethylene shade cloth (available from gemplers.com), which blocks half of the sunlight. She also sets up beach umbrellas to shade some plants at midday. Don't want to fool with adding shade cloth and umbrellas? Grow them in light afternoon shade.
Prepare the Soil
A dahlia plant prefers moist, well-drained soil that contains lots of organic matter. Every year, Ed and Kathy grind up and compost fallen leaves. In January and February, they dig these into the soil along with soil conditioner and mushroom compost. Plants growing in good soil don't need very much fertilizer.
Plant in Spring
April and May are good months. Plant the roots about 1 foot deep, spacing tall selections (over 4 feet tall) 4 to 5 feet apart and shorter ones 1 to 2 feet apart. Kathy sprinkles a teaspoon of Epsom salts and a teaspoon of Osmocote fertilizer in each hole.
Don't water dormant roots after planting until sprouts show aboveground or the roots will probably rot. After that, water only when plants look wilted in early morning before the sun hits them.
Support Your Plants
All but very short plants need to be tied to a 6-foot rebar stake driven into the ground beside them.
Make the Cut
Dahlia varieties with full, tight blooms (such as formal decorative, ball, and pompon types) make excellent, long-lasting cut flowers. "For Sunday church displays, we'll cut them on Saturday morning and make the arrangements, and they'll still look good for Wednesday night," says Kathy.
Buy dormant roots in February and March for best selection. Two great mail-order sources are dahlias.com and hilltopdahlias.com.