Dahlia in Zone 3a & 3b
Dahlia spp.
When to plant dahlia in zone 3b
Zones 3a and 3b share the same average frost dates in our data, so this page covers both.
Method: Direct sow: Direct-sow outside. Dahlia 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.
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 harvest.
Good companions
No standout companions recorded yet 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.
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 · Full companion planting guide · Full plant profile · 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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