Delphinium grandiflorum Summer Blues® | Siberian Larkspur

Delphinium grandiflorum Summer Blues®, commonly known as Siberian Larkspur, is a compact perennial delphinium with beautiful blue flowers and a naturally neat, well-proportioned habit. Growing to only around 35 cm tall, it is very different from the tall traditional delphiniums and is particularly suitable for pots, mixed containers, borders and the front of perennial flower beds.

One of the greatest advantages of Summer Blues® is its FastraX perennial breeding: plants can flower in the first year from seed without requiring vernalization. This makes it an especially interesting perennial for gardeners who want results during the first growing season.

Its compact size also makes Summer Blues® an excellent choice for smaller gardens, patios and balconies where traditional tall delphiniums may be too large.

Plant Information

• Botanical name: Delphinium grandiflorum
• Common name: Siberian Larkspur
• Variety: Summer Blues®
• Plant type: Perennial
• Flower colour: Blue
• Growth habit: Compact, upright and naturally well-shaped
• Height: Approx. 35 cm
• Exposure: Sun – partial shade
• Spring crop time: Approx. 16–20 weeks
• Flowers in the first year: Yes
• Vernalization: Not required
• Sowing period: December–May
• Seed form: Raw seed
• Hardiness zone: 3b–7b
• Use: Pots, mixed containers, borders and perennial flower beds

What Makes Summer Blues® Special?

Flowers in the first year • No vernalization required • Compact 35 cm habit • Beautiful blue flowers • Perennial • Excellent for pots • Perfect for mixed containers • Ideal for borders and the front of flower beds • Easy to grow from seed

A Delphinium That Flowers in the First Year

Summer Blues® belongs to the FastraX perennial group, meaning it can flower during the first growing season from seed without requiring a cold period.

Traditional perennial cultivation can sometimes require waiting until the following season for flowering. Summer Blues® has been selected to shorten this process, making it especially rewarding when grown from seed.

With an early sowing and suitable growing conditions, the spring crop time is approximately 16–20 weeks, or 112–140 days.

Compact – Only Around 35 cm Tall

Unlike the tall, imposing flower spikes associated with many traditional delphiniums, Summer Blues® develops a naturally compact habit and reaches only around 35 cm in height.

This compact growth makes it particularly versatile. It can be planted at the front of perennial borders, along paths and garden edges, or grown in pots where taller delphiniums would be impractical.

Its smaller size also means the plants are generally easier to integrate into mixed plantings without overwhelming neighbouring flowers.

Beautiful Blue Flowers

Summer Blues® produces charming blue flowers that create a light, airy effect above the compact foliage.

The blue colour is particularly useful in garden combinations and works beautifully with white, cream, pale yellow, pink, lavender and apricot flowers.

For a soft romantic planting, combine Summer Blues® with pale pastel shades. For stronger contrast, pair its blue flowers with warm yellow or apricot tones.

Perfect for Pots and Mixed Containers

Summer Blues® has been specifically selected for its compact habit, making it an excellent perennial for pots and mixed container arrangements.

It can be used as the upright flowering element in a container and combined with lower or trailing plants.

For larger containers, several plants can be grown together to create a fuller flowering display. Professional cultivation recommendations suggest using three plants per larger container.

Choose a pot with drainage holes and a good-quality, well-drained growing medium.

Beautiful at the Front of the Border

At approximately 35 cm tall, Summer Blues® is particularly useful for the front and middle sections of perennial flower beds.

It adds blue colour without creating the considerable height of traditional delphiniums and can be repeated throughout a border to create rhythm and continuity.

Its perennial nature means established plants can return in following seasons where winter conditions are suitable.

Growing from Seed

Summer Blues® can be successfully grown from seed and does not require vernalization before its first flowering.

For the earliest flowering, sow indoors well before the outdoor planting season.

Sowing and Germination

• Sowing period: Approximately December–May, depending on the desired flowering time and local growing conditions.
• Sowing: Sow 2–3 seeds per cell or small pot.
• Covering: Cover the seeds lightly with fine growing medium or vermiculite.
• Germination temperature: Approximately 20–22°C.
• Germination time: Approximately 14–18 days.
• Moisture: Keep the growing medium consistently moist during germination, but avoid prolonged waterlogging.

After Germination

Once the seedlings have emerged, provide plenty of light and good air circulation.

The young plants can usually be transplanted approximately 6–8 weeks after sowing, once they have developed a healthy root system.

Do not plant the young plants too deeply. Keep the crown at approximately the same level as it was growing in the seedling container.

For further growth, temperatures around 13–16°C are suitable and help produce compact, sturdy plants.

Planting Outdoors

When to plant: Harden the young plants gradually before transplanting them outdoors.

Position: Choose a location in sun to partial shade. Good light supports compact growth and abundant flowering.

Soil: Summer Blues® prefers fertile, well-drained soil. Avoid heavy locations where water remains around the roots for long periods.

Good air circulation is also beneficial, particularly when plants are grown closely together.

Important Temperature Note

Delphinium Summer Blues® prefers relatively moderate growing temperatures.

Very high temperatures above approximately 29°C can negatively affect flower development. During periods of extreme summer heat, a position protected from the strongest afternoon sun may therefore be beneficial.

Cool conditions combined with very short days can also slow flowering, which is mainly relevant during very early indoor or greenhouse production.

For home gardeners, the most important points are simple: provide good light, moderate temperatures and good air circulation.

Watering and Feeding

Watering: Keep the soil reasonably and evenly moist during active growth, but avoid permanently wet conditions. Good drainage is particularly important when growing Summer Blues® in containers.

Feeding: The variety has moderate nutrient requirements. Once seedlings are established, use a balanced fertilizer regularly at moderate strength.

Avoid excessive fertilizer concentrations and salt accumulation in the growing medium.

Growing in Pots

For container growing, use a well-drained, high-quality potting mix and a container with drainage holes.

A single plant can be grown in a smaller pot, while three plants can be combined in a larger container to create a fuller display.

Because Summer Blues® is a perennial rather than simply a seasonal bedding plant, container-grown plants can potentially be kept for future seasons where suitable winter protection and drainage are provided.

Ideal for

Pots • Patio containers • Mixed containers • Perennial borders • Front of flower beds • Garden edging • Small gardens • Balcony and terrace planting • Blue garden colour schemes

Why Grow Delphinium Summer Blues®?

Delphinium grandiflorum Summer Blues® offers the beauty of a perennial delphinium in a much more compact and versatile form.

Its approximately 35 cm height, beautiful blue flowers and suitability for pots and borders already make it an attractive garden plant. But its greatest advantage is the ability to flower in the first year from seed without vernalization.

For gardeners who love delphiniums but do not have space for very tall varieties, Summer Blues® is an excellent way to bring the distinctive blue colour and delicate character of Delphinium into pots, smaller gardens and the front of perennial borders.