Sweet William in Zone 4a & 4b
Dianthus barbatus
When to plant sweet william 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. Sweet William needs a head start most zones can't give it by direct-sowing alone.
| Start indoors | Mar 27–Apr 3 |
|---|---|
| Direct sow / transplant outside | May 8–May 15 |
| Estimated bloom | Jul 7–Jul 14 (~60 days after transplanting) |
Spacing: 4 per square foot (square-foot-gardening spacing). Mature height: 1-2 ft.
Sweet William is a cottage-garden staple, grown for dense clusters of small, fragrant flowers that often come bicolor, a ring of contrasting color around each petal's edge. It's technically a short-lived perennial or biennial, but most gardens treat it as an annual for the most reliable bloom.
How sweet william fits zone 4's season
Zone 4b's frost-free window runs about 128 days, from May 15 to September 20. Sweet William needs about 60 days from transplant to first harvest.
Good companions
No standout companions recorded yet for Sweet William.
Where to buy sweet william seeds
See why we recommend these suppliers →
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See it growing
Search YouTube for "growing sweet william" 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 Sweet William in USDA zone 4b: when to start seeds indoors, when to direct-sow, and when to expect a bloom.
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