Phlox (Annual) in Zone 3a & 3b
Phlox drummondii
Yes, phlox (annual) grows in zones 3a and 3b. Start seeds indoors Apr 25–May 2 and plant out May 23–May 30.
When to plant phlox (annual) in zone 3b
Zones 3a and 3b 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 25–May 2 |
|---|---|
| Direct sow / transplant outside | May 23–May 30 |
| Estimated bloom | Aug 1–Aug 8 (~70 days after planting) |
Spacing: 2 per square foot (square-foot-gardening spacing). Mature height: 0.5-1.5 ft.
Plant alongside it in zone 3b
These go outside within two weeks of phlox (annual) in zone 3b, so one planting day can cover them.
- NasturtiumJun 6–Jun 13
- MarigoldJun 6–Jun 13
- Bells of IrelandMay 23–May 30
- CarnationMay 23–May 30
- Orlaya (Laceflower)May 23–May 30
- RanunculusMay 23–May 30
Annual phlox is a compact, fast, and easy bedding flower in unusually bright, saturated colors, worth telling apart from the taller, perennial garden phlox that shares the common name but grows and behaves quite differently.
How phlox (annual) fits zone 3's season
Zone 3b's frost-free window runs about 98 days, from May 30 to September 5. Phlox (annual) needs about 70 days from sowing to first bloom.
Phlox (Annual) planting windows in every zone
Zone 3b 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 15–Apr 22 | May 13–May 20 | Jul 22–Jul 29 |
| 3a & 3b (your zone) | Apr 25–May 2 | May 23–May 30 | Aug 1–Aug 8 |
| 4a & 4b | Apr 10–Apr 17 | May 8–May 15 | Jul 17–Jul 24 |
| 5a & 5b | Apr 5–Apr 12 | May 3–May 10 | Jul 12–Jul 19 |
| 6a & 6b | Mar 21–Mar 28 | Apr 18–Apr 25 | Jun 27–Jul 4 |
| 7a & 7b | Mar 6–Mar 13 | Apr 3–Apr 10 | Jun 12–Jun 19 |
| 8a & 8b | Feb 18–Feb 25 | Mar 18–Mar 25 | May 27–Jun 3 |
| 9a & 9b | Jan 11–Jan 18 | Feb 8–Feb 15 | Apr 19–Apr 26 |
| 10a & 10b | Dec 26–Jan 2 | Jan 23–Jan 30 | Apr 3–Apr 10 |
| 11a & 11b | Nov 27–Dec 4 | Dec 25–Jan 1 | Mar 5–Mar 12 |
Bloom dates are about 70 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 phlox (annual).
Where to buy phlox seeds
Botanical Interests · True Leaf Market (each supplier's phlox seeds)
Varieties we recommend, and where to get them:
- 'Cherry Caramel' annual phlox (best for cut-flower stem length): Johnny's Selected Seeds describes this as having long stems and an antique look, a perfect cut flower and border plant, bred longer-stemmed than a standard bedding mix. Buy: Botanical Interests Full notes
See why we recommend these suppliers →
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See it growing
Search YouTube for "growing phlox (annual)" videos → (a live search, not a hand-picked video; results vary and aren't vetted by us)
← Back to the full zone 3b calendar · Plan your beds in the Garden Designer →
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Growing Phlox (Annual) in USDA zone 3b: when to start seeds indoors, when to direct-sow, and when to expect a bloom.
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