Nancy Parker
Where to buy dahlia seeds and bulbs: Burpee Gardening
In cold North American climates, dahlias are grown as tuberous-rooted tender perennials from small brown biennial tubers planted in spring.
These colorful, spiky flowers bloom from midsummer to first frost, when many other plants have faded. They range dramatically in size—from giant 10-inch "dinnerplate" blooms to 2-inch lollipop-style pompons—and most varieties reach 4–5 feet tall.
Though unsuited to extremely hot, humid climates (like much of Texas and Florida), dahlias brighten any sunny garden with a growing season of at least 120 days. They thrive in the cool, moist Pacific Coast climate, where blooms may be an inch larger and deeper in color.
Planting Dahlias
- Don't rush—dahlias struggle in cold soil. Wait until ground temperature reaches 60°F and all frost danger has passed (around when tomatoes go in).
- Choose full sun (6–8 hours daily). Morning sun is best. Provide wind protection.
- Rich, well-drained soil with pH 6.5–7.0 (slightly acidic) is ideal. Amend heavy soil with sand, peat moss, or bagged steer manure for drainage.
- Spacing: bedding dahlias 9–12 inches apart; smaller types (3 feet tall) 2 feet apart; tall, large-flowered types 3 feet apart.
- Dig holes slightly larger than root balls. Incorporate compost or sphagnum peat moss, plus a handful of bonemeal. Don't fertilize otherwise at planting.
- Select firm tubers with a bit of green growth—avoid wrinkled or rotten ones. Don't cut individual tubers like potatoes.
- Plant whole, eyes facing up, 6–8 inches deep. Crowns should sit just above soil level.
- Stake tall, large-flowered cultivars at planting time (5–6 foot stakes). Tie stems as they grow.
- Large dahlias and cut-flower types do best in dedicated rows, free from competition. Medium-to-low heights mix well with other summer flowers. A vegetable garden row works perfectly for cutting dahlias.
- Blooms appear ~8 weeks after planting (mid-July onward).
- Some gardeners start tubers indoors a month early for a jump on the season.
- Don't water tubers right after planting—this encourages rot. Wait until sprouts emerge.
- Don't mulch with bark or similar—sprouting is hindered. Apply slug/snail bait instead.
Seasonal Care
- Don't water until plants appear; overwatering rots tubers. Once established, water deeply 2–3 times weekly for 30+ minutes (more in hot, dry climates).
- Feed with low-nitrogen liquid fertilizer (5-10-10 or 10-20-20) after sprouting, then every 3–4 weeks from mid-summer to early autumn. Avoid over-fertilizing, especially nitrogen—risks include few/no blooms, weak tubers, or rot.
- Large blooms may need attention before/after rain (water-filled blooms) or wind.
- Bedding dahlias: pinch growing point above third leaf set for bushiness; deadhead faded flowers. No staking or disbudding needed.
- Taller dahlias: stake at planting. Moderately pinch, disbranch, disbud, and deadhead for 3+ months of showy display.
- Foliage blackens with first frost.
- Hardy to zone 8. In zone 8, cut back and mulch deeply for overwintering. Elsewhere, lift and store tuberous roots. (Some zone 7 gardeners report success with heavy mulch.)
Pests and Diseases
- Slugs/snails: Bait 2 weeks after planting and continue all season.
- Spider mites: Spray from late July through September. Consult local garden center for recommended sprays.
- Earwigs and cucumber beetles: Eat petals but don't harm plants.
- Aphids
- Deer: Plant deer-resistant companions nearby.
- Powdery mildew: Common in fall. Preventative spray from late July to August.
Harvest and Storage: Lifting Tubers
In cold regions, dig tubers in early fall for winter storage.
Dahlias may overwinter in ground in USDA Zone 8. In frost-prone areas (most of Zone 5), a killing frost helps bulbs go dormant.
- Cut foliage to 2–4 inches above ground. Lift and separate clumps.
- Gently shake off soil.
- Remove rotten tubers; dry clumps upside down naturally.
- Pack in loose, fluffy material (vermiculite, dry sand, Styrofoam peanuts).
- Store in well-ventilated, frost-free place at 40–45°F (35–50°F acceptable).
- In spring, separate tubers from parent clump and restart.
- If storage seems daunting, simply buy new tubers each spring.
Recommended Varieties
Choosing a favorite dahlia is like browsing a button box—endless color, size, and shape options. Popular picks:
- 'Bishop of Llandaff' — small, intense scarlet flowers with handsome dark-burgundy foliage.
- 'Miss Rose Fletcher' — elegant spiky pink cactus type with 6-inch globes of long, quilled, shell-pink petals.
- 'Bonne Esperance' ('Good Hope') — foot-tall dwarf with 1½-inch rosy-pink daisies all summer (reminiscent of Victorian bedding dahlias; debuted 1948).
- 'Kidd's Climax' — 10-inch "dinnerplate" flowers with hundreds of pink petals suffused with gold.
- 'Jersey's Beauty' — 7-foot pink giant with hand-sized flowers, bringing energy to the fall garden.
Wit & Wisdom
The dahlia was named for Anders Dahl (botanist), born March 17, 1751.
The Dahlia you brought to our isle
Your praises forever shall speak
'Mid gardens as sweet as your smile
And colour as bright as your cheek.
—Lord Holland (1773–1840)
