Plant Sunflowers in Zone 3b
Seed-starting, transplant & harvest dates for USDA Zone 3b
Zone 3b averages 128 frost-free days, running from a last spring frost around May 13 to a first fall frost around September 18. Sunflowers needs roughly 80 days from planting out to first harvest, so it uses about 63 percent of that window. Sunflowers is a half-hardy crop, which is what decides where in the window it belongs.
Sunflowers resents transplanting and hates cold soil, so direct sow around May 20, after the Zone 3b last frost has passed and the soil has warmed.
Fall planting: sunflowers in Zone 3b
Sunflowers has no useful fall window in Zone 3b. Sunflowers need a long run of warm, long days and will not finish from a late-summer sowing outside frost-free zones.
Sunflowers need a long run of warm, long days and will not finish from a late-summer sowing outside frost-free zones.
Fall dates are counted backward from the Zone 3b average first frost, not forward from a sowing date. See the fall planting calendar by zone for the full method.
Spring vs fall sunflowers in Zone 3b
| Planting | Sow or start | In the ground | Harvest |
|---|---|---|---|
| Spring | May 20 | May 20 | Aug 8 |
| Fall | — | — | — |
Sunflowers in nearby zones
Further reading on sunflowers
- Last frost date and what to plant before it
Why sunflowers can go out before your last frost, and how far before.
- Companion planting chart
What to plant with sunflowers and what to keep away from it.
Other crops in Zone 3b
Frequently asked questions
When should I start sunflowers in Zone 3b?
Direct sow outdoors around May 20.
Can I direct sow sunflowers in Zone 3b?
Yes, direct sow around May 20.
Can I plant sunflowers in the fall in Zone 3b?
Sunflowers has no useful fall window in Zone 3b. Sunflowers need a long run of warm, long days and will not finish from a late-summer sowing outside frost-free zones.
Will sunflowers survive frost in Zone 3b?
No. Sunflowers is a half-hardy crop and a single light frost ends it, so every Zone 3b planting has to finish before the average first frost.