Dahlia Growing Guide
Dahlia spp.
In most of Canada, dahlia tubers won't survive winter in the ground — digging them up before the first hard frost isn't optional the way it is in milder climates.
Light
Full sun, minimum 6-8 hours daily
Soil
Well-drained, fertile soil rich in organic matter
Water
Regular, consistent watering once shoots emerge
Hardiness
Tubers hardy outdoors only in zones 8+; dig and store elsewhere
Mature size
1-6 ft depending on variety
Growth rate
Fast once established; blooms from midsummer to frost
Dahlias reward the extra effort of digging and storing their tubers each fall with weeks of some of the showiest cut flowers in the garden, from midsummer right up until frost. Across most of Canada, the tubers can't survive winter in the ground, so successful dahlia growing really comes in two parts: getting them planted and staked well in spring, and storing them properly over winter.
Planting tubers
- Plant tubers after all risk of frost has passed and soil has warmed, since cold, wet soil can rot tubers before they sprout
- Plant with the eye (growth point) facing up, about 4-6 inches deep, laying larger tubers on their side
- Space tubers 18-24 inches apart depending on the mature size of the variety
- Hold off watering right after planting until shoots emerge above soil, to reduce the risk of rot in cool spring soil
Staking & support
- Install stakes at planting time for tall varieties, so you don't damage the developing tuber by driving a stake in later
- Use a sturdy 4-6 ft stake for taller varieties and loosely tie the main stem as it grows
- A single stake works for smaller varieties; taller or heavier-flowered types often do better with a small cage or corral of 3-4 stakes
- Pinch young plants back to about 12 inches to encourage bushier growth and more flowering stems
Watering, feeding & deadheading
- Water consistently once shoots are up and growing, increasing during hot, dry spells — dahlias are thirsty plants in full bloom
- Feed with a balanced or lower-nitrogen fertilizer through the season to support flowering rather than excess foliage
- Deadhead spent blooms regularly to keep the plant producing new flowers instead of setting seed
- Mulch around the base to conserve moisture and suppress weeds
Digging & storing tubers over winter
- Dig tubers after the first light frost blackens the foliage but before a hard freeze reaches the tubers themselves, typically mid-to-late fall across most of Canada
- Cut stems back to a few inches, gently lift the whole clump with a garden fork, and shake off excess soil
- Let tubers air-dry (cure) in a cool, dry, shaded spot for a few days before storage
- Store in a box layered with peat moss, vermiculite, or dry wood shavings, in a cool (4-10°C), dark, frost-free location such as a basement or unheated room
- Check stored tubers periodically through winter, removing any that show rot and lightly misting if they start to shrivel excessively
Common problems
- Tubers rotting in storage: usually from excess moisture or damage during digging — cure properly before storage and inspect regularly
- Slugs and earwigs chewing new spring growth: hand-pick in the evening or use targeted baits around emerging shoots
- Powdery mildew late in the season: improve airflow with adequate spacing and avoid overhead watering
- Weak, floppy stems: often insufficient staking or too much shade — stake early and ensure at least 6 hours of direct sun
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Frequently asked questions
In most of Canada, yes — dahlia tubers aren't reliably winter-hardy outside of the mildest coastal zones, and ground freezing will kill them if left in place. Dig after the first light frost and store indoors over winter.
More plant guides
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- Holly
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- Juniper
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