Pacific Giant Delphinium, a gorgeous tall larkspur

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Spikes up to two metres tall, packed with large white, violet and blue flowers that give off a subtle fragrance: the Pacific Giant delphinium (Delphinium elatum ‘Pacific’) is among the finest of border and cutting plants. Give it moist, fertile soil in a spot sheltered from strong winds, and the display runs for nearly four months.

The giant Pacific delphinium’s large, eye-catching flowers densely cover the flower spike, emitting a subtle fragrance. The blooming occurs in summer and lasts for 100 to 120 days (nearly 4 months!).

Giant delphinium thrives along fences and mixed borders in sunny gardens.

Giant delphinium is perfect to pick beautiful cut flowers. It fits in small gardens, and copes well in windy areas where other large perennial plants are more prone to damage. However, remember to stake the plants to protect them from stronger winds.

Planting Pacific delphinium

Delphinium Pacific cultivars grow best in moist, fertile soil in a sheltered location away from strong winds. Giant delphinium prefers cool summers. Hot and dry summers are not ideal as they often cause powdery mildew issues.

While giant delphinium needs sunlight, it is better not to plant them wherever it gets too hot in the garden. Add plenty of organic matter or compost to the planting area: it’ll help retain moisture. Plant the delphiniums at ground level, not too deep. With good growing conditions and a summery climate, delphiniums can be absolutely fabulous.

Due to their heavy flower spikes upheld by slender, hollow stems, gusts of wind and rain can be a problem.

Sowing Pacific delphiniums

Pacific Giant delphinium is surprisingly easy to grow from seeds. Some varieties will even bloom in their first year! Seeds germinate easily, within 10-15 days, and quickly develop into robust plants.

• Simply sprinkle the seeds into small pots.
• Cover them with a bit of compost.
• Mist to moisten.
• Cover everything with plastic film (bag, etc.) tied down with an elastic band. This creates a better germination environment, like a miniature greenhouse.

Once the risk of frost has passed and the plant is of reasonable size:

• Plant the mixed-color seedlings about 1 to 2 feet apart (30 to 60 cm).
• Protect them from slugs.

Once well settled-in, Pacific Delphinium reliably grows back every year. The single main task in terms of care is helping the tall flowers stay upright early in the season, with stakes.

Which group of giant delphinium to choose

Giant delphiniums fall into a few clear groups, and the one you pick decides how tall the plant gets and how much support it will need. Compare them before you sow, especially if your garden is exposed.

If your plot is windy, the shorter groups will save you a great deal of staking.

Care, growing, and fertilizer

When cultivating Delphinium Pacific Giant, consider that:

• You’re dealing with quite a hardy herbaceous perennial plant: roots can withstand frosty winters down to 14°F (-10 °C).
• In late autumn and winter, the plant dies back completely and regrows each spring.
• Expect a few to die off completely, it’s normal.
• Water during the growing season.
• Fertilizer application is optional but beneficial in spring. If the soil is rich in organic matter, you can skip fertilizing alltogether.

Diseases and Problems

Pacific Giant candle larkspur requires protection against slugs. You need to pay careful attention to slug protection. Slugs are attracted to tender, fresh shoots that emerge in spring. Protecing against slugs is essential.

Staking Giant Delphinium

All delphiniums need staking as soon as they start growing and establishing themselves. Summer winds and rain can damage flower spikes. The flowers get heavy with rainwater, and it’s difficult to anchor plants deep enough to prevent stems from breaking, especially in strong winds. Delphiniums have hollow and brittle stems that are easily damaged.

• When inserting tall stakes or poles into the ground next to a Pacific Giant Delphinium, be careful not to damage the delicate stems.
• Set the stakes up early in the growing season to minimize risk of damage.
• Use flexible ties.
• Do not tie them too tightly (it may damage the stem).
• Leave room for the stem to grow as it continues to develop.
• For single-flowered varieties, place a stake alongside the flower and use a flexible tie to attach the flower stem to the stake.

For a bouquet of giant delphiniums, it may be easier to create a simple cage using 3 to 5 stakes and then use flexible ties to connect the stems to the supports. You can also use flexible branches, such as those from a Cornus, to create a round support.

Carefully check the variety, as many giant delphiniums can grow very tall. Some varieties of Delphinium Pacific Giant, once established, can reach over 6 feet (1.5 m)! Tall stakes are necessary to support the blooms.

If your garden is exposed and prone to windy conditions, it may be more practical to grow shorter varieties.

Varieties of Pacific Giant Delphinium

There are three main groups of giant delphiniums:

• Belladonna has single flowers and reaches 4 feet (1.2 m).
• Elatum has single, double, or eyed flowers and is the most commonly cultivated group. Within this group, there are short, medium, and tall varieties that grow between 4 and 6 feet tall (1.5 m and 2 m).
• Various hybrids that are short-lived annuals or biennials. They often have colorful names like ‘King Arthur’, ‘Blue Bird’…

Dwarf Elatum strains such as Magic Fountains reach roughly half the height of a full Pacific Giant and usually stand up without stakes.

Within the Pacific series the colours are named: Black Knight is deep violet, Galahad pure white, Summer Skies pale blue, and King Arthur violet with a white eye.

Belladonna types carry looser, branched spikes that shrug off wind and rain far better than the dense Elatum candles.