Delphinium in Zone 5a & 5b
Delphinium elatum
Yes, delphinium grows in zones 5a and 5b. Set out nursery plants May 31–Jun 7.
When to plant delphinium in zone 5b
Zones 5a and 5b share the same average frost dates, so this page covers both.
Method: Buy as a start: Buy as a nursery start and transplant outside. It's slow or unreliable from seed, so most gardeners skip seed-starting it entirely.
| Start indoors | Not started from seed; buy as a nursery start |
|---|---|
| Direct sow / transplant outside | May 31–Jun 7 |
| Estimated bloom | Oct 28–Nov 4 (~150 days after transplanting) |
Spacing: 1 per square foot (square-foot-gardening spacing). Mature height: 3-6 ft.
Plant alongside it in zone 5b
These go outside within two weeks of delphinium in zone 5b, so one planting day can cover them.
- NasturtiumMay 17–May 24
- MarigoldMay 17–May 24
- Hyacinth Bean VineMay 31–Jun 7
- Angelonia (Summer Snapdragon)May 24–May 31
- Bee BalmMay 24–May 31
- Black-Eyed Susan VineMay 24–May 31
Delphinium produces some of the tallest, most dramatic flower spikes of any garden annual or perennial, in blues and purples that are hard to find elsewhere in a flower bed. It also comes with a serious caveat: every part of the plant is toxic if ingested.
How delphinium fits zone 5's season
Zone 5b's frost-free window runs about 148 days, from May 10 to October 5. Delphinium needs about 150 days from transplant to first bloom.
Delphinium 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 | Buy as a start | Jun 20–Jun 27 | Nov 17–Nov 24 |
| 4a & 4b | Buy as a start | Jun 5–Jun 12 | Nov 2–Nov 9 |
| 5a & 5b (your zone) | Buy as a start | May 31–Jun 7 | Oct 28–Nov 4 |
| 6a & 6b | Buy as a start | May 16–May 23 | Oct 13–Oct 20 |
| 7a & 7b | Buy as a start | May 1–May 8 | Sep 28–Oct 5 |
| 8a & 8b | Buy as a start | Apr 15–Apr 22 | Sep 12–Sep 19 |
| 9a & 9b | Buy as a start | Mar 8–Mar 15 | Aug 5–Aug 12 |
| 10a & 10bFall window | Buy as a start | Sep–Nov | ~150 days after transplanting |
Bloom dates are about 150 days after the sow or plant-out date.
Good companions
No well-established companions for delphinium.
Where to buy delphinium starts
Delphinium is almost always bought as a nursery start rather than seeded. Check a local nursery or garden center; we haven't vetted online start/plant suppliers yet.
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See it growing
Search YouTube for "growing delphinium" videos → (a live search, not a hand-picked video; results vary and aren't vetted by us)
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Growing Delphinium in USDA zone 5b: when to start seeds indoors, when to direct-sow, and when to expect a bloom.
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