Lobelia in Zone 5a & 5b
Lobelia erinus
Yes, lobelia grows in zones 5a and 5b. Start seeds indoors Mar 8–Mar 15 and plant out May 17–May 24.
When to plant lobelia in zone 5b
Zones 5a and 5b share the same average frost dates, so this page covers both.
Method: Start indoors: Start indoors from seed, then transplant outside. It needs a head start most zones can't give it by direct-sowing alone.
| Start indoors | Mar 8–Mar 15 |
|---|---|
| Direct sow / transplant outside | May 17–May 24 |
| Estimated bloom | Aug 5–Aug 12 (~80 days after transplanting) |
Spacing: 4 per square foot (square-foot-gardening spacing). Mature height: 4-8 in.
Plant alongside it in zone 5b
These go outside within two weeks of lobelia in zone 5b, so one planting day can cover them.
- NasturtiumMay 17–May 24
- MarigoldMay 17–May 24
- Ageratum (Flossflower)May 17–May 24
- Annual Geranium (Pelargonium)May 17–May 24
- Butterfly Weed (Asclepias)May 17–May 24
- Campanula (Bellflower)May 17–May 24
Lobelia is the smallest flower here and one of the earliest to start indoors, which catches people out.
How lobelia fits zone 5's season
Zone 5b's frost-free window runs about 148 days, from May 10 to October 5. Lobelia needs about 80 days from transplant to first bloom.
Lobelia 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 |
|---|---|---|---|
| 3a & 3b | Mar 28–Apr 4 | Jun 6–Jun 13 | Aug 25–Sep 1 |
| 4a & 4b | Mar 13–Mar 20 | May 22–May 29 | Aug 10–Aug 17 |
| 5a & 5b (your zone) | Mar 8–Mar 15 | May 17–May 24 | Aug 5–Aug 12 |
| 6a & 6b | Feb 21–Feb 28 | May 2–May 9 | Jul 21–Jul 28 |
| 7a & 7b | Feb 6–Feb 13 | Apr 17–Apr 24 | Jul 6–Jul 13 |
| 8a & 8b | Jan 21–Jan 28 | Apr 1–Apr 8 | Jun 20–Jun 27 |
| 9a & 9b | Dec 14–Dec 21 | Feb 22–Mar 1 | May 13–May 20 |
| 10a & 10b | Nov 28–Dec 5 | Feb 6–Feb 13 | Apr 27–May 4 |
Bloom dates are about 80 days after the sow or plant-out date, not after starting seeds indoors.
Good companions
No well-established companions for lobelia.
Where to buy lobelia seeds
Botanical Interests · True Leaf Market · Burpee (each supplier's lobelia seeds)
See why we recommend these suppliers →
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See it growing
Search YouTube for "growing lobelia" 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 Lobelia in USDA zone 5b: when to start seeds indoors, when to direct-sow, and when to expect a bloom.
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