Dahlias are the undisputed queens of the late summer garden, producing an astonishing variety of flowers from dinner-plate-sized blooms to delicate pompons in virtually every color except blue. A single dahlia tuber planted in spring can grow into a 4-foot-tall plant producing dozens of cut-worthy flowers from midsummer through the first hard frost. While they require a bit more attention than some perennials, the spectacular payoff makes dahlias one of the most rewarding flowers you can grow.
Choosing Dahlia Tubers
Dahlias are classified by flower form and size. Dinnerplate dahlias (8 to 12 inches across) are the showstoppers — varieties like Café au Lait (creamy blush), Thomas Edison (deep purple), and Kelvin Floodlight (bright yellow) are perennial favorites. Decorative dahlias (4 to 8 inches) are the most popular garden type. Ball and pompon dahlias produce perfectly round, tightly-petaled flowers ideal for arrangements. Cactus and semi-cactus types have spiky, rolled petals for dramatic texture. For beginners, start with 5 to 10 tubers of mixed types to discover your preferences.
Planting Dahlias
Plant dahlia tubers outdoors after all danger of frost has passed and soil temperature reaches 60 degrees Fahrenheit — typically 2 to 4 weeks after your last frost date. Dig a hole 6 to 8 inches deep and lay the tuber horizontally with the eye (growing point) facing up. Cover with just 2 to 3 inches of soil initially, then gradually fill in the hole as the shoot grows. This prevents rotting in cold, wet spring soil. Space tubers 18 to 24 inches apart for smaller varieties and 24 to 36 inches for dinnerplates. Do not water at planting — wait until sprouts emerge, then begin regular watering.
Pinching for More Blooms
When the plant reaches 12 to 16 inches tall with 3 to 4 sets of leaves, pinch out the center growing tip just above the top set of leaves. This single action is the most important thing you can do for dahlia production — it forces the plant to branch into multiple stems, potentially doubling or tripling your flower count. It feels counterintuitive to remove the tip of a healthy plant, but the results are dramatic. You can also disbud (remove the two smaller side buds flanking each central bud) for fewer but larger individual blooms — essential for dinnerplate varieties.
Staking and Support
Most dahlias over 3 feet tall need staking to prevent the heavy flower-laden stems from snapping in wind or rain. Install stakes at planting time (not later, to avoid damaging tubers) — a single sturdy 5-foot stake per plant works well. Tie the main stem loosely with soft garden twine as it grows. For a more natural look, use a cage made from concrete reinforcing wire or a tomato cage.
Overwintering Tubers
In zones 8 and warmer, dahlias can be left in the ground with a thick layer of mulch over winter. In zones 7 and colder, tubers must be dug and stored indoors. After the first killing frost blackens the foliage, cut stems to 4 inches and carefully dig up the clump of tubers with a garden fork. Rinse off soil, let them dry for a day in a sheltered location, then store in a box of slightly damp peat moss, vermiculite, or wood shavings in a cool (40 to 50 degrees), dark, frost-free location like a basement or garage. Check monthly and mist if tubers begin to shrivel. Replant in spring.
Frequently Asked Questions
When do dahlias bloom?
Dahlias typically begin blooming 8 to 12 weeks after planting, with peak production from August through October. They get better as the season progresses, producing their best blooms in the cool nights of early fall.