How to Grow Delphinium
Delphinium At a Glance
Difficulty
Moderate
Category
Flower
Sun Exposure
Full Sun
Frost Tolerance
Frost Hardy
Cold Hardiness
Survives to -34°C
Plant Family
Ranunculaceae
Growing Season
Cool Season
Plant Lifecycle
Perennial
How to Start It
★ Recommended for beginners
The easiest start is a young plant from a garden centre, set out in spring around your last frost date, 50 cm from its neighbours. Plant it with the crown (where the stems meet the roots) right at soil level, never buried, and push in a tall stake at the same time.
Delphiniums love cool summers, which suits much of Canada well. Each plant only lives a few years, so take cuttings or divide it now and then to keep them going.
When To Start
Delphinium likes cool weather. Sow it in early spring, as soon as the ground can be worked.
We do not have exact sowing dates for this one yet.
When should you plant Delphinium?
Your planting dates depend on your local climate. Sign up and add your location to unlock personalized dates.
Your Delphinium Planting Window
Start planting
May 15, 2026
Last chance
Sep 10, 2026
Your Delphinium Calendar
Set your location to turn these into exact dates and reminders.
Plant delphiniums in full sun, out of strong wind
Around your last frost· every year
Stake delphiniums now and pick slugs off the shoots
1 week after your last frost· every year· optional
Cut finished delphinium spikes to the base for more flowers
60 days after your last frost· every year· optional
Water your new delphinium plants well while they settle in. Deep and slow is best.
About 1 days after you plant it
How is your delphinium settling in? Tie the stems loosely to the stake as they grow.
About 30 days after you plant it
Delphinium check! Once a flower spike fades, cut it off for a chance at more blooms.
About 90 days after you plant it
The Journey Ahead
Delphinium's Lifecycle
Seedling
Mature Plant
Seed Production
Step 1
Prepare Your Space
50 cm
Plant Spacing
30 cm
Row Spacing
Vertical Growing
No.
Succession Planting
No.
Good Companions
Bad Companions
Step 2
Planting & Sprouting
Growing Tips
- 1Give delphiniums full sun and shelter from strong wind, which snaps the tall hollow stems.
- 2Plant them in rich, well-drained soil with plenty of compost mixed in.
- 3Water deeply once a week so the soil stays moist, and spread mulch to keep the roots cool.
- 4Feed with compost tea or worm castings in spring as the shoots grow, and again after the first flowers.
- 5Tie each tall stem to a stake while it is still short, because once a spike flops or snaps it cannot be fixed.
- 6Slugs love the young spring shoots, so pick them off by hand at dusk every few days.
- 7All parts of delphinium are poisonous to people and pets if eaten, so keep children and animals away from the plants.
Seedling Phase
Step 3
Growth & Maturity
150 cm
Mature Height
50 cm
Mature Width
Pests to Watch For
Diseases to Watch For
Mature Plant
Step 4
Harvesting
When to Pick
Spires bloom early summer; cut the spent stalk for a second autumn flush
How to Harvest
- 1Cut spikes for a vase when about a third of the flowers on them have opened.
- 2Once a spike has finished flowering, cut it right down to the base.
- 3Feed and water well after that cut, and new shoots often bring a smaller second round of flowers in late summer.
- 4Thin crowded clumps in spring to the strongest few shoots for bigger spikes.
- 5Cut all the stems down to the ground after the first hard frost in fall.
Step 5
Saving Seeds
How to Save Seeds
Delphinium seeds are poisonous, so wear gloves and keep them away from children and pets. Many delphiniums are hybrids, so seedlings may differ in colour and height from the parent. Leave a few spikes on the plant until the pods turn brown and dry, then snip them into a paper bag before they split open. Shake out the seeds and store them labelled in a sealed jar in the fridge, since they lose their strength quickly and are best sown within a year.
Seed Production
Still have a question?
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