Delphiniums Pacific Giant Series
Delphinium elatum 'Pacific Giant'
These towering cottage garden classics produce magnificent spikes of densely packed flowers in shades of blue, purple, pink, and white, reaching impressive heights that create stunning vertical drama. The Pacific Giant series is renowned for producing the tallest and most robust delphiniums, with flower spikes that can extend 3-4 feet in length. Though challenging to grow, their spectacular display rewards dedicated gardeners with one of the most breathtaking sights in the flower garden.
Sun
Full sun
Zones
3–7
USDA hardiness
Height
3-5 feet
Planting Timeline
Showing dates for Delphiniums Pacific Giant Series in USDA Zone 7
All Zone 7 flower →Zone Map
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Delphiniums Pacific Giant Series · Zones 3–7
Growing Details
Zone-by-Zone Planting Calendar
| Zone | Indoor Start | Transplant | Direct Sow | Harvest |
|---|---|---|---|---|
| Zone 3 | April – May | June – July | June – August | — |
| Zone 4 | March – April | June – June | June – July | — |
| Zone 5 | March – April | May – June | May – July | — |
| Zone 6 | March – April | May – June | May – July | — |
| Zone 7 | February – March | April – May | April – June | — |
| Zone 8 | February – March | April – May | April – June | — |
| Zone 9 | January – February | March – April | March – May | — |
| Zone 10 | January – January | February – March | February – April | — |
| Zone 1 | May – June | July – August | July – September | — |
| Zone 2 | April – May | June – July | June – August | — |
| Zone 11 | January – January | January – February | January – March | — |
| Zone 12 | January – January | January – February | January – March | — |
| Zone 13 | January – January | January – February | January – March | — |
Complete Growing Guide
Light: Full sun (6 or more hours of direct sunlight a day). Soil: High Organic Matter. Soil pH: Alkaline (>8.0). Drainage: Good Drainage. Height: 3 ft. 0 in. - 5 ft. 0 in.. Spread: 2 ft. 0 in. - 3 ft. 0 in.. Spacing: 12 inches-3 feet, 3 feet-6 feet. Growth rate: Medium. Maintenance: Medium. Propagation: Seed. Regions: Mountains, Piedmont.
Harvesting
Edibility: Toxic if eaten.
Storage & Preservation
Fresh delphinium cuts should be processed immediately after harvesting for maximum longevity. Place stems in deep, cool water (around 40-50°F) and store in a cool location away from direct sunlight. They'll maintain quality for up to a week when properly conditioned.
For preservation, delphiniums excel at air drying due to their dense flower structure. Harvest spikes when flowers are just beginning to open, strip lower leaves, and hang upside down in small bundles in a warm, dry, dark location with good air circulation. They'll dry completely in 2-3 weeks, retaining much of their original color intensity.
Silica gel drying produces superior results for individual florets, maintaining better color and form. Press individual flowers in a flower press or heavy book between absorbent paper for craft projects. The dried flowers work beautifully in wreaths, potpourri, and permanent arrangements, though remember all parts remain toxic even when dried.
History & Origin
Origin: Europe to Mongolia
Advantages
- +Attracts: Butterflies, Hummingbirds
- +Edible: Toxic if eaten.
Considerations
- -Toxic (Flowers, Leaves, Stems): Medium severity
- -Causes contact dermatitis
Companion Plants
Catmint (Nepeta spp.) is the most practical pairing here. It sprawls low and covers the bare ankles of delphinium stems, and its scent slows aphid colonization — aphids move onto Pacific Giants fast if nothing deters them. Roses share the same preference for soil pH around 7.0–7.5 and the same deep-watering schedule, so the two plants don't undercut each other the way shallow-rooted annuals can. Larkspur and campanula fill the mid-border without crowding the root zone.
Black walnut is a non-starter. Juglone — the allelopathic compound the roots and decomposing husks release — is reliably lethal to delphiniums, and the damage doesn't require direct root contact. Skip brassicas in the same bed too: they're heavy nitrogen feeders, and delphiniums already need consistent fertility to push those 4–5 foot spikes through summer.
Plant Together
Roses
Delphiniums provide natural support structure and both benefit from similar growing conditions
Larkspur
Similar care requirements and creates layered cottage garden effect with complementary flower forms
Peonies
Bloom timing complements delphiniums and both prefer rich, well-drained soil
Campanula
Provides ground cover and contrasting flower shape while sharing similar moisture needs
Astilbe
Thrives in partial shade created by tall delphiniums and adds textural contrast
Monkshood
Similar growing requirements and extends the blue color palette in the garden
Hollyhocks
Creates dramatic height variation and both are classic cottage garden plants
Catmint
Repels pests and provides low-growing complement to tall delphinium spikes
Keep Apart
Black Walnut
Produces juglone toxin that can severely damage or kill delphiniums
Crown Imperial Fritillaria
Allelopathic compounds can inhibit delphinium growth and establishment
Brassicas
Compete for similar nutrients and can attract pests that also damage delphiniums
Pests & Disease Resistance
Resistance
Susceptible to crown rot, bacterial black spot, and powdery mildew
Common Pests
Aphids, spider mites, slugs, snails, delphinium leaf miner
Diseases
Crown rot, bacterial black spot, powdery mildew, fusarium wilt
Troubleshooting Delphiniums Pacific Giant Series
What you'll see, why it happens, and what to do about it.
Stems collapsing at the base, with dark brown or black mushy tissue at the crown, often appearing after a wet spring stretch
Likely Causes
- Crown rot (Sclerotium rolfsii or Phytophthora spp.) — triggered by waterlogged soil or mulch piled against the crown
- Planting too deep, which keeps the crown wet and poorly ventilated
What to Do
- 1.Pull any mulch back at least 3 inches from the base of the plant
- 2.Dig and discard heavily affected plants — don't compost them; crown rot persists in soil
- 3.Improve drainage before replanting: work in coarse grit or perlite and raise the bed 4–6 inches if needed
Ragged, irregular holes in leaves and flower buds at or near ground level, most visible in the morning after a damp night
Likely Causes
- Slugs or snails — Pacific Giants are a preferred target, especially in cool, moist springs
- Delphinium leaf miner (Phytomyza delphinivora) — produces winding pale tunnels inside leaves rather than clean holes, but often misidentified at first glance
What to Do
- 1.Set out iron phosphate bait (Sluggo) around the base of plants at dusk; reapply after rain
- 2.If tunneling is visible inside the leaf tissue, pinch off and bag the affected leaves to break the leaf miner's life cycle
- 3.Keep the area around the crown clear of debris — slugs shelter under it during the day