Dahlia in Zone 3a & 3b
Dahlia spp.
Yes, dahlia grows in zones 3a and 3b. Plant it outside Jun 13–Jun 20.
When to plant dahlia in zone 3b
Zones 3a and 3b share the same average frost dates, so this page covers both.
Method: Direct sow: Direct-sow outside. It doesn't transplant well, or doesn't need the extra time indoors.
| Start indoors | Not typically started indoors |
|---|---|
| Direct sow / transplant outside | Jun 13–Jun 20 |
| Estimated bloom | Sep 11–Sep 18 (~90 days after direct-sowing) |
Spacing: 1 per square foot (square-foot-gardening spacing). Mature height: 1-5 ft.
Plant alongside it in zone 3b
These go outside within two weeks of dahlia in zone 3b, so one planting day can cover them.
- NasturtiumJun 6–Jun 13
- MarigoldJun 6–Jun 13
- Angelonia (Summer Snapdragon)Jun 13–Jun 20
- Black-Eyed Susan VineJun 13–Jun 20
- Cleome (Spider Flower)Jun 13–Jun 20
- ColeusJun 13–Jun 20
Dahlia is the one flower in this garden that doesn't start as seed at all. It grows from a tuber, planted like a potato, which changes the whole rhythm of how it goes in the ground and comes out at season's end. Blooms run from small pompoms to dinner-plate-sized flower heads, in nearly every color except true blue, on plants that range from 1 to 5 feet depending on type.
How dahlia fits zone 3's season
Zone 3b's frost-free window runs about 98 days, from May 30 to September 5. Dahlia needs about 90 days from sowing to first bloom.
Dahlia planting windows in every zone
Zone 3b is highlighted. Useful for comparing against a neighbouring zone, or for a garden somewhere else.
| Zone | Start indoors | Sow or plant out | Bloom |
|---|---|---|---|
| 3a & 3b (your zone) | Not usually | Jun 13–Jun 20 | Sep 11–Sep 18 |
| 4a & 4b | Not usually | May 29–Jun 5 | Aug 27–Sep 3 |
| 5a & 5b | Not usually | May 24–May 31 | Aug 22–Aug 29 |
| 6a & 6b | Not usually | May 9–May 16 | Aug 7–Aug 14 |
| 7a & 7b | Not usually | Apr 24–May 1 | Jul 23–Jul 30 |
| 8a & 8b | Not usually | Apr 8–Apr 15 | Jul 7–Jul 14 |
| 9a & 9b | Not usually | Mar 1–Mar 8 | May 30–Jun 6 |
| 10a & 10bSpring window | Not usually | Feb–Apr | ~90 days after direct-sowing |
| 11a & 11b | Not usually | Jan 15–Jan 22 | Apr 15–Apr 22 |
Bloom dates are about 90 days after the sow or plant-out date.
Good companions
No well-established companions for dahlia.
Where to buy dahlia bulbs
We haven't vetted bulb/tuber suppliers yet. Our seed-supplier list below doesn't carry these. The growing-guide source cited above is a good starting point for where to buy.
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See it growing
Search YouTube for "growing dahlia" videos → (a live search, not a hand-picked video; results vary and aren't vetted by us)
← Back to the full zone 3b calendar · Plan your beds in the Garden Designer →
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Growing Dahlia in USDA zone 3b: when to start seeds indoors, when to direct-sow, and when to expect a bloom.
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