Growing Delphinium: A Complete Profile
By Growing Home Greens Team · July 29, 2026
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.
Starting it (from a nursery pot, not a seed packet)
Delphinium is almost always grown from a nursery start rather than seed. Its seed needs cold stratification and germinates slowly, often not blooming until its second year even when it does sprout. Set transplants out about 3 weeks after your last frost, and expect around 150 days to bloom. It struggles in hot summers above zone 7 under a normal spring planting. Zone 10 gardeners get around this by planting in fall instead, for bloom over the cooler winter months.
Keeping the spikes upright
Toppled stalks are the most common frustration with delphinium, and staking at planting time, not after the plant has already grown tall, prevents most of it. If staking every year sounds like too much upkeep, a compact type like Magic Fountains still needs support but carries less top-heavy risk than a full-height Pacific Giant.
Because every part of the plant is toxic if ingested, keep it out of reach of pets and children who might chew on it. This is worth deciding on before you place it, not after.
Back of the bed, away from kids and pets
Delphinium has no well-established companion pairings, and nothing it needs to be kept away from. Given its height and toxicity, place it toward the back of a bed or against a support in the Garden Designer, away from where kids or pets typically reach.
Sources: Magic Fountains Mix Delphinium Seed, Johnny’s Selected Seeds.
Companion planting guide for Delphinium · Find your planting dates
Typically viable in USDA zones 3-10. Not sure your zone? Look it up by ZIP code.
Mature height: 3-6 ft
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.
When to plant delphinium, by zone
Every zone delphinium grows in. Pick your zone in the header and it will be highlighted here. Each zone links to its full page.
| 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 | 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.
See exact start-indoors, direct-sow, and harvest dates for your zone →
How many Delphinium plants fit per square foot?
Spacing: 1 per square foot (square-foot-gardening spacing). Mature height: 3-6 ft.
Varieties worth considering
- Magic Fountains (Delphinium elatum, Dwarf Pacific type): Johnny's Selected Seeds lists it at 36-48 inches against the 5-6 feet a full-size Pacific Giant reaches, with the same wide color range. It still needs support, delphinium spikes are heavy no matter the height, but a shorter plant is a shorter lever arm, and it's noticeably less prone to snapping over in wind than the tall types. (source) Buy seeds: True Leaf Market
- Pacific Giant 'Galahad': Chicago Botanic Garden lists this white-flowered Pacific Giant at up to 6 feet, taller than Magic Fountains' dwarf 3-4 feet. Grow it if you want the full dramatic height and have a wall or sturdy stake ready, not a compromise on staking effort. (source)
- Pacific Giant 'Black Knight': Also a full-height Pacific Giant per Chicago Botanic Garden, deep indigo-blue rather than Galahad's white. Same staking commitment as Galahad, just a different color at the top of the spike. (source)
Why each variety is listed comes from the source shown next to it. We haven't grown these ourselves yet, so treat this as a research-backed starting point, not a personal endorsement. The buy links are separate from those sources: they go to seed suppliers that sell that exact variety, and we may earn a commission on some of them.
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: A tall, dramatic spike flower that needs staking, patience, and (in most households) placement well away from pets and kids.
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