Carthamus (Safflower) in Zone 4a & 4b
Carthamus tinctorius
Yes, carthamus (safflower) grows in zones 4a and 4b. Start seeds indoors Apr 17–Apr 24 and plant out May 15–May 22.
When to plant carthamus (safflower) in zone 4b
Zones 4a and 4b share the same average frost dates, so this page covers both.
Method: Either: Start indoors for an earlier harvest, or direct-sow outside for less fuss. Either works.
| Start indoors | Apr 17–Apr 24 |
|---|---|
| Direct sow / transplant outside | May 15–May 22 |
| Estimated bloom | Aug 13–Aug 20 (~90 days after planting) |
Spacing: 4 per square foot (square-foot-gardening spacing). Mature height: 1.5-2 ft.
Plant alongside it in zone 4b
These go outside within two weeks of carthamus (safflower) in zone 4b, so one planting day can cover them.
- NasturtiumMay 22–May 29
- MarigoldMay 22–May 29
- African DaisyMay 15–May 22
- Amaranthus (Love-Lies-Bleeding)May 15–May 22
- Ammi (False Queen Anne's Lace)May 15–May 22
- Ammobium (Winged Everlasting)May 15–May 22
Carthamus, better known as safflower, is a thistle-like cut flower historically grown as an oilseed and dye crop, with bright orange-yellow blooms that hold their color well once dried.
How carthamus (safflower) fits zone 4's season
Zone 4b's frost-free window runs about 128 days, from May 15 to September 20. Carthamus (safflower) needs about 90 days from sowing to first bloom.
Carthamus (Safflower) planting windows in every zone
Zone 4b 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 | Apr 22–Apr 29 | May 20–May 27 | Aug 18–Aug 25 |
| 3a & 3b | May 2–May 9 | May 30–Jun 6 | Aug 28–Sep 4 |
| 4a & 4b (your zone) | Apr 17–Apr 24 | May 15–May 22 | Aug 13–Aug 20 |
| 5a & 5b | Apr 12–Apr 19 | May 10–May 17 | Aug 8–Aug 15 |
| 6a & 6b | Mar 28–Apr 4 | Apr 25–May 2 | Jul 24–Jul 31 |
| 7a & 7b | Mar 13–Mar 20 | Apr 10–Apr 17 | Jul 9–Jul 16 |
| 8a & 8b | Feb 25–Mar 4 | Mar 25–Apr 1 | Jun 23–Jun 30 |
| 9a & 9b | Jan 18–Jan 25 | Feb 15–Feb 22 | May 16–May 23 |
| 10a & 10b | Jan 2–Jan 9 | Jan 30–Feb 6 | Apr 30–May 7 |
| 11a & 11b | Dec 4–Dec 11 | Jan 1–Jan 8 | Apr 1–Apr 8 |
Bloom dates are about 90 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 carthamus (safflower).
Where to buy carthamus seeds
None of the seed suppliers we list carries carthamus seeds right now. A local garden center or a specialty seed house is the place to look.
See why we recommend these suppliers →
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See it growing
Search YouTube for "growing carthamus (safflower)" videos → (a live search, not a hand-picked video; results vary and aren't vetted by us)
← Back to the full zone 4b calendar · Plan your beds in the Garden Designer →
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Growing Carthamus (Safflower) in USDA zone 4b: when to start seeds indoors, when to direct-sow, and when to expect a bloom.
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