Hybrid

Guardian Blue

Delphinium elatum

Photo: Anton Hartinger · Wikimedia Commons · (Public domain)

Uniform flowering time and plant height allows for efficient harvesting. The Guardian series is bred to perform well under short days for greenhouse production. Guardian also performs well in our field trials, blooming under long days. Vigorous plants with excellent bloom and stem quality for cut flowers. Also suitable for garden beds and landscaping. Bloom color is dark royal blue with a white bee (flower structure at the center of each bloom). Attracts bees and butterflies. This species of delphinium is also known as candle larkspur. Perennial in Zones 3-7.

Harvest

105-125d

Days to harvest

📅

Sun

Full sun

☀️

Zones

3–7

USDA hardiness

🗺️

Height

3-5 feet

📏

Planting Timeline

Zone:

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Start Indoors

Transplant

Direct Sow

Start Indoors

Transplant

Direct Sow

Showing dates for Guardian Blue in USDA Zone 7

All Zone 7 flower →

Zone Map

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Guardian Blue · Zones 3–7

What grows well in Zone 7? →

Growing Details

Difficulty

Easy

Spacing18-24 inches

SoilWell-drained loam

WaterRegular

SeasonPerennial

ColorDark royal blue with white center

Zone-by-Zone Planting Calendar

Zone	Indoor Start	Transplant	Direct Sow	Harvest
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	—
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	—

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

Guardian Blue reaches harvest at 105 - 125 days from sowing per Johnny's Selected Seeds.

Edibility: Toxic if eaten.

Storage & Preservation

For cut flowers, place Guardian Blue delphiniums in a clean vase with cool water (35-45°F) immediately after harvest. Keep in a cool location away from direct sunlight and ripening fruit. Change water every 2-3 days and remove lower leaves to prevent bacterial growth. Fresh blooms last 7-14 days in a vase. To preserve longer: (1) air-dry upright stems in a dark, well-ventilated space for 2-3 weeks; (2) glycerin preservation by absorbing a glycerin-water solution for prolonged color retention; (3) freeze-drying for specialty arrangements, though this requires professional equipment.

History & Origin

Guardian Blue is an F1 hybrid developed through controlled cross-pollination. Listed in the Johnny's Selected Seeds catalog.

Origin: Europe to Mongolia

Advantages

+Uniform flowering time and height enable efficient mechanical harvesting operations
+Thrives under both short and long day conditions for flexible production
+Dark royal blue color with white bee attracts pollinators naturally
+Vigorous plants produce excellent quality stems suitable for premium cut flowers
+Perennial in Zones 3-7 allows multi-year garden and landscape installations

Considerations

-Delphiniums susceptible to powdery mildew in humid greenhouse conditions
-Requires well-draining soil; poorly drained areas cause root rot issues
-Tall plants may need staking or support in windy locations
-Relatively long production cycle of 105-125 days ties up growing space

Companion Plants

Marigolds and Sweet Alyssum do the most work here — marigolds repel aphids that cluster on delphinium stems, while alyssum draws in parasitic wasps that knock back caterpillar pressure from species like Polychrysia moneta. Catmint and lavender make good low-growing neighbors because they share Guardian Blue's preference for sharp drainage and don't compete hard at root depth. Fennel causes problems through root exudates that stunt nearby plants, and eucalyptus releases allelopathic volatile compounds that suppress germination and establishment — give both a wide berth.

Plant Together

Marigolds

Repel nematodes and aphids while attracting beneficial insects

Sweet Alyssum

Attracts beneficial insects and provides ground cover protection

Nasturtiums

Act as trap crop for aphids and cucumber beetles

Lavender

Repels moths, fleas, and mosquitoes with aromatic oils

Catmint

Deters ants, aphids, and rodents while attracting pollinators

Zinnia

Attracts ladybugs and other beneficial predatory insects

Cosmos

Attracts beneficial insects and provides structural support

Chives

Repel aphids and improve soil health with sulfur compounds

Keep Apart

Black Walnut

Releases juglone toxin that inhibits growth of many flowers

Eucalyptus

Allelopathic compounds suppress growth of nearby plants

Fennel

Inhibits growth of most garden plants through allelopathy

Pests & Disease Resistance

Common Pests

Spider mites, powdery mildew moths, slugs

Diseases

Powdery mildew, crown rot, leaf spot

Troubleshooting Guardian Blue

What you'll see, why it happens, and what to do about it.

White powdery coating on leaves and stems, usually appearing first on older growth mid-season

Likely Causes

Powdery mildew (Erysiphe spp.) — thrives in warm days and cool nights with poor airflow
Crowded spacing under 18 inches that traps humidity around the crown

What to Do

1.Cut off and bag the worst-affected stems — don't compost them
2.Spray remaining foliage with a diluted potassium bicarbonate solution (1 tablespoon per gallon of water) every 7 days
3.Next season, space plants at the full 24 inches and avoid overhead irrigation

Stems collapsing at the soil line, crown turning soft and brown, often after a wet stretch

Likely Causes

Crown rot (Sclerotium rolfsii or Phytophthora spp.) — triggered by waterlogged soil or heavy mulch piled against the crown
Poor drainage in clay-heavy beds

What to Do

1.Dig and discard the affected plant — crown rot doesn't recover, and leaving it in the ground infects neighbors
2.Before replanting, work in 2–3 inches of coarse grit or compost to open up the soil structure
3.Keep mulch pulled back at least 3 inches from the crown

Ragged holes chewed in young leaves and flower buds, damage concentrated near soil level and worst after rain

Likely Causes

Slugs — they feed at night and hide under debris during the day
Delphinium moth (Polychrysia moneta) caterpillars on upper foliage

What to Do

1.Set out iron phosphate bait (Sluggo or equivalent) around the base of plants after any rainfall
2.Check stems and buds after dark with a flashlight for caterpillars; pick them off by hand
3.Clear leaf litter and debris from around the crowns — slugs need daytime shelter to persist

Frequently Asked Questions

How long do Guardian Blue delphiniums last as cut flowers?▼

Guardian Blue blooms typically last 7-14 days in a vase with proper care. To extend vase life, change water every 2-3 days, keep flowers in a cool location (35-45°F), and remove lower leaves to prevent bacterial growth. Using flower preservative and ensuring clean stems at harvest will maximize longevity.

Is Guardian Blue delphinium good for beginner gardeners?▼

Yes, Guardian Blue is excellent for beginners. It's rated as 'Easy' difficulty and doesn't require specialized care. The variety thrives in full sun with well-drained soil and standard watering. Its uniform flowering time and vigorous growth make it reliable even for novice growers in zones 3-7.

Can you grow Guardian Blue delphiniums in containers?▼

While primarily bred for garden beds and field production, Guardian Blue can grow in containers, though it may be less ideal than in-ground planting. Use large containers (15+ gallons) with well-drained soil and ensure adequate sunlight (6+ hours daily). Container-grown plants may require more frequent watering and monitoring.

When should I plant Guardian Blue delphinium seeds?▼

Guardian Blue should be started indoors 6-8 weeks before your last frost date, or direct sown outdoors after the last frost danger passes. Seeds typically germinate in 7-14 days under cool conditions. Plant in full sun locations and space plants 18-24 inches apart for optimal air circulation and bloom quality.

What zone can Guardian Blue delphiniums grow in?▼

Guardian Blue is a perennial delphinium hardy in USDA Zones 3-7. It performs exceptionally well in cooler climates and can return year after year. In warmer zones (8+), it's typically grown as an annual. The variety thrives in both greenhouse production under short days and field gardens under long days.

Do Guardian Blue delphiniums attract pollinators?▼

Yes, Guardian Blue delphiniums are excellent pollinator plants. They attract bees and butterflies with their dark royal blue flowers and distinctive white bee (central flower structure). Their vertical spike growth and abundant blooms make them valuable additions to pollinator gardens and landscapes seeking to support beneficial insects.