Fragrant summer lilac - Buddleja davidii 'Empire Blue' (Butterfly Bush)

Buddleja davidii 'Empire Blue' is a variety of ornamental shrub in the Scrophulariaceae family, commonly known as the “butterfly bush” (Butterfly Bush). This plant is valued for its spectacular, fragrant flowers, which attract butterflies, bees, and other pollinating insects, making it an excellent choice for gardens that aim to support biodiversity.

Flower appearance

• Shape: The flowers are small and tubular, grouped in long, dense panicles (large clusters) that can reach 20–25 cm in length. They are arranged at the ends of the branches, creating an impressive visual effect, and are major nectar producers—a true attraction for bees and butterflies.
• Colour: They have a deep intense blue-violet shade (sometimes described as a true blue), with a small orange “eye” in the centre of each flower, offering a subtle yet attractive contrast.
• Fragrance: They emit a sweet, fruity fragrance that enhances their appeal to pollinators and adds a pleasant note to the garden.
• Flowering period: It blooms abundantly from June to October, sometimes until the first frost, especially if spent flowers are removed regularly (deadheading), which encourages continuous flowering.

Growth characteristics

• Height: It grows compactly, reaching a height of 1.5–2 metres and a similar width, making it smaller and easier to integrate into gardens than other Buddleja davidii varieties.
• Foliage: The leaves are lance-shaped and silvery grey-green, with a fine texture and a slightly downy appearance on the undersides. They are arranged opposite one another along the branches and provide an elegant backdrop for the vibrant flowers.
• Vigour: It is a fast-growing shrub, but remains well proportioned, with arching branches that give it a graceful, airy form.

Growing conditions

• Exposure: It prefers full sun for abundant flowering, but also tolerates partial shade, although it will produce fewer flowers.
• Soil: It requires well-drained, moderately fertile to fertile soil and adapts to various types, including clay and sandy soils, provided that water does not remain stagnant. It tolerates a variable pH (acidic, neutral, or alkaline).
• Watering: Moderate watering is required. Once established, it is relatively drought-tolerant, but its performance declines in excessively wet conditions.
• Pruning: Severe pruning is recommended in February–March, cutting the plant back to 15–30 cm above ground level, to encourage vigorous growth and abundant flowering on new wood. Removing spent flowers throughout the season prolongs flowering. This pruning also helps delay flowering, reducing the risk of the plant being affected by late frosts.

Care and hardiness

• Hardiness: It is hardy to temperatures as low as −20°C (USDA zones 5–9), but in colder climates it may die back to ground level in winter, behaving like a herbaceous perennial. In spring, it resumes vigorous growth from the roots.
• Fertilisation: A balanced fertiliser applied in spring supports flowering, but is not strictly necessary in fertile soil.
• Pests and diseases: It may be affected by aphids, spider mites, or mullein moth, but is generally resilient when well ventilated. It may develop mould in damp, poorly drained conditions.

Garden uses

Buddleja 'Empire Blue' is ideal for borders, cottage gardens, or as a standalone plant in mixed landscapes. Thanks to its compact size, it is also suitable for containers on terraces or balconies. Its blue-violet flowers combine beautifully with yellow plants (e.g. Kniphofia) or white plants (e.g. white roses), creating vibrant contrasts. It is also excellent as a cut flower, thanks to its fragrance and durability.

Origin

Buddleja davidii is native to China and Japan, where it grows naturally on rocky slopes and in disturbed areas. The 'Empire Blue' variety was developed in the United Kingdom in the 20th century as part of horticultural selections intended to enhance the plant’s intense colours and hardiness. Although there are no precise details about the exact year or breeder, 'Empire Blue' is one of the first varieties to popularise true blue shades in Buddleja cultivation and is valued by gardeners for its colour and reliability.