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Buddleja davidii ‘Blue Knight’ (Butterfly Bush)

Butterfly Bush 'Blue Knight', Summer Lilac 'Blue Knight', Buddleja 'Blue Knight'

Buddleja davidii 'Blue Knight' (Monarch Series), Butterfly Bush Blue Knight, Summer Lilac Blue Knight
Buddleja davidii 'Blue Knight' (Monarch Series), Butterfly Bush Blue Knight, Summer Lilac Blue Knight

Buddleja davidii ‘Blue Knight’ is an enchanting addition to any garden, offering a profusion of deep blue flowers that stand out against its silver-green foliage. This butterfly bush, part of the Monarch® Series.

Buddleja ‘Blue Knight’: An In-depth Look

Native: This plant is a cultivar of Buddleja davidii, native to China. ‘Blue Knight’, like many cultivars, was bred for specific horticultural traits.

Plant Type and Habit: This deciduous shrub has a bushy, rounded habit, with arching branches that give it a casual yet elegant appearance. It’s typically grown as a border plant or as a stand-alone specimen in a garden.

Size: This butterfly bush can reach 3-4 feet in height (90-120 cm) and 6-7 feet in spread (180-210 cm).

Flowers: Remarkably elongated flower clusters, spanning 10 to 12 inches (25-30 cm), emerge as a soft lavender purple and mature into a deeper blue-purple. With both new and older blooms present simultaneously, the clusters showcase a captivating two-tone appearance that adds a dynamic visual effect.

Bloom Time: The blooming period extends from mid-summer into the autumn, providing a long-lasting display of color and interest. This extended blooming season is one of the reasons butterfly bushes are so prized in the garden.

Foliage: The foliage of opposite, lance-shaped, mint-green leaves provides a soft backdrop for the vibrant flower spikes.

Uses: With its moderate size and attractive features, this butterfly bush is well-suited for a variety of garden applications. It works well when planted in butterfly gardens, coastal gardens, cottage gardens, or city gardens in mixed borders or as a specimen plant, providing both aesthetic appeal and ecological benefits.

Hardiness: This plant is hardy in USDA zones 5-10, showcasing its ability to withstand a variety of climates.

Pollinators: The flowers attract various pollinators, especially bees, butterflies, and hummingbirds.

Toxicity: There is no known toxicity associated with this plant, making it safe for planting in gardens and communal spaces.

Deer and Rabbit: Butterfly bush is generally resistant to deer, making it a hassle-free choice for gardeners contending with these critters.

Drought: This plant shows a good level of drought tolerance once established, though regular watering during prolonged dry spells will encourage better growth and flowering.

Invasiveness: Buddleja davidii varieties have been known to be invasive in certain areas, spreading via their numerous seeds.

Butterfly Bush Growing Tips

Light: Full sun is ideal for Buddleja; it needs at least 6 hours of direct sunlight daily to flourish and produce abundant flowers.

Soil: Well-drained soil is crucial. Buddleja is adaptable to various soil types but thrives in soil enriched with organic matter.

Water: Establish a regular watering schedule. Buddleja is somewhat drought-tolerant but performs best with consistent moisture, especially in the first growing season.

Fertilizer: This plant needs no fertilizer other than a thin layer of compost spread over the root zone each spring.

Pruning: Prompt removal of spent flower spikes will usually promote blooms until frost. Prune in early to mid-spring to allow time for the new growth to mature and flower in the same year. Avoid pruning in winter, as it may lead to frost damage of new shoots.

Propagation: Propagate by hardwood cuttings in autumn or by semi-hardwood cuttings in summer

Pests and Diseases: Watch out for aphids, spider mites, and caterpillars. Buddleja can also be affected by root rot, downy mildew, and leaf spot.

Requirements

Hardiness 5 - 10
Heat Zones 1 - 9
Climate Zones 2, 2A, 2B, 3, 3A, 3B, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, H1
Plant Type Shrubs
Plant Family Scrophulariaceae
Genus Buddleia
Common names Butterfly Bush
Exposure Full Sun
Season of Interest Summer (Mid, Late)
Fall
Height 3' - 4'
(90cm - 120cm)
Spread 6' - 7'
(180cm - 210cm)
Spacing 72" - 84"
(180cm - 210cm)
Maintenance Low
Water Needs Average
Soil Type Chalk, Clay, Loam, Sand
Soil pH Acid, Alkaline, Neutral
Soil Drainage Well-Drained
Characteristics Cut Flowers, Fragrant, Showy
Tolerance Drought, Deer
Attracts Bees, Butterflies, Hummingbirds
Garden Uses Beds And Borders
Garden Styles Gravel and Rock Garden, Informal and Cottage, Coastal Garden, City and Courtyard
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Alternative Plants to Consider

Buddleja davidii ‘Dark Dynasty’ (Butterfly Bush)
Buddleja davidii ‘Queen of Hearts’ (Butterfly Bush)
Buddleja davidii ‘Princess Pink’ (Butterfly Bush)
Buddleja davidii ‘Prince Charming’ (Butterfly Bush)
Buddleja Humdinger® Little Angel (Butterfly Bush)
Buddleja Humdinger® Lavender Cupcake (Butterfly Bush)

Recommended Companion Plants

Echinacea (Coneflower)
Sedum (Stonecrop)
Hemerocallis (Daylilies)

Find In One of Our Guides or Gardens

Native Plant Alternatives to Buddleja davidii (Butterfly Bush)
Best Flowers to Attract Hummingbirds
While every effort has been made to describe these plants accurately, please keep in mind that height, bloom time, and color may differ in various climates. The description of these plants has been written based on numerous outside resources.
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Requirements

Hardiness 5 - 10
Heat Zones 1 - 9
Climate Zones 2, 2A, 2B, 3, 3A, 3B, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, H1
Plant Type Shrubs
Plant Family Scrophulariaceae
Genus Buddleia
Common names Butterfly Bush
Exposure Full Sun
Season of Interest Summer (Mid, Late)
Fall
Height 3' - 4'
(90cm - 120cm)
Spread 6' - 7'
(180cm - 210cm)
Spacing 72" - 84"
(180cm - 210cm)
Maintenance Low
Water Needs Average
Soil Type Chalk, Clay, Loam, Sand
Soil pH Acid, Alkaline, Neutral
Soil Drainage Well-Drained
Characteristics Cut Flowers, Fragrant, Showy
Tolerance Drought, Deer
Attracts Bees, Butterflies, Hummingbirds
Garden Uses Beds And Borders
Garden Styles Gravel and Rock Garden, Informal and Cottage, Coastal Garden, City and Courtyard
How Many Plants
Do I Need?
Explore Great Plant Combination Ideas
Buddleja (Butterfly Bush)
Not sure which Buddleja (Butterfly Bush) to pick?
Compare Now

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