Petunia in Zone 3a & 3b
Petunia × hybrida
Yes, petunia grows in zones 3a and 3b. Start seeds indoors Mar 28–Apr 4 and plant out Jun 13–Jun 20.
When to plant petunia in zone 3b
Zones 3a and 3b share the same average frost dates, so this page covers both.
Method: Start indoors: Start indoors from seed, then transplant outside. It needs a head start most zones can't give it by direct-sowing alone.
| Start indoors | Mar 28–Apr 4 |
|---|---|
| Direct sow / transplant outside | Jun 13–Jun 20 |
| Estimated bloom | Aug 22–Aug 29 (~70 days after transplanting) |
Spacing: 1 per square foot (square-foot-gardening spacing). Mature height: 0.5-1 ft.
Plant alongside it in zone 3b
These go outside within two weeks of petunia 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
Petunias take the longest lead time of any flower on this list. Seed goes in about 9 weeks before last frost, and it needs light to germinate, so it's surface-sown rather than buried. That long runway is the price for having sizable, blooming plants ready to set out once the weather turns: a trailing or mounding 6- to 12-inch plant covered in trumpet-shaped flowers across a wide color range.
How petunia fits zone 3's season
Zone 3b's frost-free window runs about 98 days, from May 30 to September 5. Petunia needs about 70 days from transplant to first bloom.
Petunia 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 |
|---|---|---|---|
| 2a & 2b | Mar 18–Mar 25 | Jun 3–Jun 10 | Aug 12–Aug 19 |
| 3a & 3b (your zone) | Mar 28–Apr 4 | Jun 13–Jun 20 | Aug 22–Aug 29 |
| 4a & 4b | Mar 13–Mar 20 | May 29–Jun 5 | Aug 7–Aug 14 |
| 5a & 5b | Mar 8–Mar 15 | May 24–May 31 | Aug 2–Aug 9 |
| 6a & 6b | Feb 21–Feb 28 | May 9–May 16 | Jul 18–Jul 25 |
| 7a & 7b | Feb 6–Feb 13 | Apr 24–May 1 | Jul 3–Jul 10 |
| 8a & 8b | Jan 21–Jan 28 | Apr 8–Apr 15 | Jun 17–Jun 24 |
| 9a & 9b | Dec 14–Dec 21 | Mar 1–Mar 8 | May 10–May 17 |
| 10a & 10bFall window | Jul–Jan | Sep–Mar | ~70 days after transplanting |
| 11a & 11b | Oct 30–Nov 6 | Jan 15–Jan 22 | Mar 26–Apr 2 |
Bloom dates are about 70 days after the sow or plant-out date, not after starting seeds indoors.
Zone 2 sows before zone 3 here, which looks wrong and is not. USDA zones rank winter cold, not season length, and zone 2 is mostly interior Alaska, where hard winters come with warm summers. More on what a zone measures.
Good companions
No well-established companions for petunia.
Where to buy petunia seeds
Botanical Interests · True Leaf Market · Burpee (each supplier's petunia seeds)
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See it growing
Search YouTube for "growing petunia" 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 Petunia in USDA zone 3b: when to start seeds indoors, when to direct-sow, and when to expect a bloom.
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