Petunia in Zone 4a & 4b
Petunia × hybrida
When to plant petunia in zone 4b
Zones 4a and 4b share the same average frost dates in our data, so this page covers both.
Method: Start indoors: Start indoors from seed, then transplant outside. Petunia needs a head start most zones can't give it by direct-sowing alone.
| Start indoors | Mar 13–Mar 20 |
|---|---|
| Direct sow / transplant outside | May 29–Jun 5 |
| Estimated bloom | Aug 7–Aug 14 (~70 days after transplanting) |
Spacing: 1 per square foot (square-foot-gardening spacing). Mature height: 0.5-1 ft.
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 4's season
Zone 4b's frost-free window runs about 128 days, from May 15 to September 20. Petunia needs about 70 days from transplant to first harvest.
Good companions
No standout companions recorded yet for Petunia.
Where to buy petunia seeds
See why we recommend these suppliers →
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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 4b calendar · Full companion planting guide · Full plant profile · Plan your beds in the Garden Designer →
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Growing Petunia in USDA zone 4b: when to start seeds indoors, when to direct-sow, and when to expect a bloom.
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