Tithonia (Mexican Sunflower) in Zone 5a & 5b
Tithonia rotundifolia
Yes, tithonia (Mexican sunflower) grows in zones 5a and 5b. Start seeds indoors Mar 29–Apr 5 and plant out May 24–May 31.
When to plant tithonia (Mexican sunflower) in zone 5b
Zones 5a and 5b 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 | Mar 29–Apr 5 |
|---|---|
| Direct sow / transplant outside | May 24–May 31 |
| Estimated bloom | Aug 20–Aug 27 (~88 days after planting) |
Spacing: about 2 square feet per plant (square-foot-gardening spacing). Mature height: 4-6 ft.
Plant alongside it in zone 5b
These go outside within two weeks of tithonia (Mexican sunflower) in zone 5b, so one planting day can cover them.
- NasturtiumMay 17–May 24
- MarigoldMay 17–May 24
- Angelonia (Summer Snapdragon)May 24–May 31
- Bee BalmMay 24–May 31
- Black-Eyed Susan VineMay 24–May 31
- Chrysanthemum (Garden Mum)May 24–May 31
Tithonia, better known as Mexican sunflower, is a fast-growing, heat-loving annual that produces vivid orange-red blooms on tall, sturdy stems late in the season, just as many other cut flowers are winding down.
How tithonia (Mexican sunflower) fits zone 5's season
Zone 5b's frost-free window runs about 148 days, from May 10 to October 5. Tithonia (Mexican sunflower) needs about 88 days from sowing to first bloom.
Tithonia (Mexican Sunflower) planting windows in every zone
Zone 5b 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 8–Apr 15 | Jun 3–Jun 10 | Aug 30–Sep 6 |
| 3a & 3b | Apr 18–Apr 25 | Jun 13–Jun 20 | Sep 9–Sep 16 |
| 4a & 4b | Apr 3–Apr 10 | May 29–Jun 5 | Aug 25–Sep 1 |
| 5a & 5b (your zone) | Mar 29–Apr 5 | May 24–May 31 | Aug 20–Aug 27 |
| 6a & 6b | Mar 14–Mar 21 | May 9–May 16 | Aug 5–Aug 12 |
| 7a & 7b | Feb 27–Mar 6 | Apr 24–May 1 | Jul 21–Jul 28 |
| 8a & 8b | Feb 11–Feb 18 | Apr 8–Apr 15 | Jul 5–Jul 12 |
| 9a & 9b | Jan 4–Jan 11 | Mar 1–Mar 8 | May 28–Jun 4 |
| 10a & 10b | Dec 19–Dec 26 | Feb 13–Feb 20 | May 12–May 19 |
| 11a & 11b | Nov 20–Nov 27 | Jan 15–Jan 22 | Apr 13–Apr 20 |
Bloom dates are about 88 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 tithonia (Mexican sunflower).
Where to buy tithonia seeds
True Leaf Market · Burpee (each supplier's tithonia seeds)
Varieties we recommend, and where to get them:
- 'Goldfinger': The smallest of the three per Clemson, orange-gold flowers on a 2-2.5 foot plant, an even more compact option than Fiesta del Sol for the tightest spaces. Buy: True Leaf Market Full notes
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See it growing
Search YouTube for "growing tithonia (Mexican sunflower)" videos → (a live search, not a hand-picked video; results vary and aren't vetted by us)
← Back to the full zone 5b calendar · Plan your beds in the Garden Designer →
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Growing Tithonia (Mexican Sunflower) in USDA zone 5b: when to start seeds indoors, when to direct-sow, and when to expect a bloom.
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