About Dahlias
Dahlias are the undisputed queens of the late-summer garden. Double dahlias produce elaborate, many-petalled blooms that resemble pom-poms or dinner plates in stunning pinks, peaches, and blues. Single dahlias offer simpler, daisy-like flowers with open centers that pollinators love, in warm peach and striking red-and-white bicolors. Both bloom prolifically from midsummer until the first hard frost — often the last flowers standing in the garden.
Planting Tubers
Plant dahlia tubers outdoors after the last frost, once soil temperature reaches at least 60°F. Dig a hole 6 to 8 inches deep in rich, well-drained soil. Place the tuber horizontally with the eye (growth point) facing up — it's similar to a potato eye. Cover with 2 to 3 inches of soil initially, and backfill as shoots grow. Space 12 to 18 inches apart for bushier varieties, up to 24 inches for dinner-plate types. Do not water until sprouts emerge — moisture on dormant tubers causes rot.
Growing Conditions
Choose a spot with full sun (6 to 8 hours daily). Dahlias need rich, well-drained soil — amend with compost or aged manure before planting. They're heavy feeders that produce their best in fertile ground. Good drainage is critical — soggy soil rots tubers. Dahlias grow best in zones 7-10 (lift and store tubers in colder zones).
Staking & Pinching
Install stakes at planting time — tall varieties with large blooms absolutely need support, and staking after the fact risks damaging roots. Use 5-to-6-foot garden stakes. When plants reach 12 inches tall, pinch the center growing tip to encourage branching and more flowers. Continue to tie stems to stakes as they grow.
Watering, Feeding & Overwintering
Once growing, water 2 to 3 times per week, more during hot weather. Feed every 2 to 3 weeks with a balanced fertilizer, switching to a high-phosphorus formula once buds form. Deadhead spent blooms to keep new flowers coming. After the first killing frost, cut stems to 4 inches, dig up tubers, let them dry for a day, then store in peat moss or vermiculite in a cool (40-50°F), dry location until spring. Dahlias make spectacular cut flowers (5-7 day vase life) and pair wonderfully with sunflowers, cosmos, and lisianthus in arrangements.