Butterfly Bush ‘Black Knight’ (Buddleia ‘Black Knight’)

The Black Knight Butterfly bush is a must-have to attract butterflies and hummingbirds to the garden. The shrub is an excellent addition, and the butterflies and birds will enjoy the sweet nectar from the flower clusters. The butterfly bushes you can grow as a single shrub or use them in a mass planting. The deciduous shrub also received an Award of Garden Merit from the Royal Horticultural Society. But how do you care for this great shrub to ensure it keeps thriving in cottage gardens to enjoy the gorgeous scented blooms, nearly black flowers, and fall flower color?

Please keep reading to find out, and read our care guide on the Butterfly bush ‘Black Knight’.

I. Appearance and Characteristics

Buddleja davidii is called the butterfly bush, and the Black Knight is a cultivar with nearly black flowers. The parent plant is a deciduous shrub native to China growing on stream banks.

It can reach up to eight feet tall and wide when not killed by cold winter temperatures. It grows with a bushy habit with arching stems and showy, fragrant flower clusters and can grow vigorously.

It is classified as a noxious weed in Hawaii, Oregon, Washington, and California. The Black Knight Butterfly bush forms cone-shaped panicles looking like lilacs in purple with orange-yellow throats.

The sweet nectar attracts butterflies and hummingbirds to the garden. When the blooms are left alone, it develops a two-valved seed capsule that splits open when ripe and is self-seeding. The foliage is a sage green above with white tomentose color beneath.

Another common name for the Black Knight Butterfly Bush is the Summer Lilac Black Knight, with another genus listed as Buddleia.

II. How to Grow and Care

Sunlight

Choose a spot in the garden where your Black Knight Butterfly bush can receive eight hours of full sun in the morning. In warm climates with extreme heat, provide your plant with bright sunlight in the morning with afternoon shade.

Temperature and Humidity

As a hybrid, the Black Knight Butterfly bush tolerates cold temperatures and can survive winter.

It may act as a herbaceous perennial in some USDA hardiness zones and die back to the ground in winter.

But with the spreading habit and rapid growth, it is not a problem and still provides fall flowers before winter arrives. These blooms make for exceptional cut flowers.

Watering

Originating from a habitat with moderate moisture, butterfly bush ‘Black Knight’ thrives in conditions that mimic its native environment. This species exhibits a preference for consistent moisture but is resilient to brief dry spells. Its watering schedule should reflect this balance, ideally with hydration provided twice a week. As an outdoor plant renowned for attracting pollinators, butterfly bush ‘Black Knight’ benefits significantly from rainwater during its peak growing season, which enhances its flowering potential and supports its lush, deciduous nature.

Soil

As you know, most plants prefer growing in well-drained instead of firm soil. The same applies to the Black Knight, whether grown as potted perennials or in the landscape.

The shrub prefers a neutral to alkaline soil rich in nutrients. It can tolerate alkaline soil pH levels of up to 8.5, but a range between 5.5 to 7.0 is ideal.

It can cope with most types of soil, even chalk, and grows well in coastal areas as it is tolerant to salt. But it does not do well in clay soil.

Fertilizing

Though butterfly bush ‘Black Knight’ can tolerate poor soils, the addition of fertilizer will improve growth and quantity of blooms. Using a good quality rose fertilizer is a good choice, as it will usually have a high potash (potassium) content, which encourages flowering.
Another alternative is to use fish, blood, and bone meal with the addition of homemade wood ash. Using the meal on its own would be too high in nitrogen and would result in strong growth. If many blooms are desired, the ash is a necessary addition.

Planting Instructions

The best time to plant the butterfly bush is when the soil surface warms up after the last frost. Hence, late spring or early summer is the best time for planting. The recommended planting instructions are as follows:

• Dig a hole three times wider than the root ball and a little deeper if you use additions like fertilizer, limestone chippings, or compost.
• If your soil type is too acidic, the limestone chippings can help amend it and provide good drainage for clay soil.
• If you fertilize when planting, you need not feed your butterfly bush for the first two years.
• You can apply the feed around the root zone.
• Plant your butterfly bush at the same level as in the container you received your plant.
• If you need to move your plant, the best time is in late autumn or early winter.

Pruning

Pruning should be carried out in early to mid-spring. Earlier in the spring will allow more time for butterfly bush ‘Black Knight’ to recover, which should result in more blooms. Cut back flowering stems from the previous year to within 1-2 buds of the older, woodier framework of the plant. Remove any thin, dead, or weak growth. Cutting the plant annually back to around 61 cm in height will keep the plant from getting too large.

If the plant is in an exposed and windy site, reduce its height by about half in the autumn to avoid wind damage. Alternate-leaved butterfly bush and orange ball tree both flower on the previous year’s growth, so spring pruning would likely reduce the number of flowers that year. These types benefit from pruning after flowering. Deadheading regularly will encourage flowering.

Propagation

Butterfly bush ‘Black Knight’ is a robust and attractive flowering shrub prevalent among gardeners for its appeal to butterflies. The most effective method to propagate butterfly bush ‘Black Knight’ is via cuttings. Softwood cuttings taken in the late spring or early summer are preferable. Select healthy, non-flowering shoots for the best success rate, and ensure cuttings are about 4-6 inches long with several sets of leaves.

Cutting the base at a slight angle can facilitate rooting which should be done in a well-draining, moist soil mix, under partial shade. Keeping the cuttings humid, through the use of a plastic cover and regular misting, helps establish roots. Once rooted, gradually acclimatize the new plants to outdoor conditions before transplanting them to their final growing location.

Pests and Diseases

Like most plants, the Black Knight Butterfly bush can be bothered by aphids, spider mites, and scale insects. You can use insecticidal soap or neem oil to resolve these issues. Another problem is flower clusters withering.

• Aging Butterfly Bushes

The butterfly bush flowers can dry out due to sudden environmental changes as your plant has completed its natural flowering period. If your plant is aging, you can do nothing about it to slow the process down, and best to harvest the seeds or take a cutting.

• Brown Spots and Underwatering

Another problem is brown spots appearing as new growth appears, and it does not need any treatment. If the problems become severe, they can be treated by applying organic fungicides. You can dissolve 1/2 a tsp. of baking soda in a teaspoon of liquid soap in a gallon of water in a spray bottle.

Spray the solution on the foliage to coat the top and bottom of the lance-shaped pointed leaves. Lastly, leaves can wilt for different reasons, and the first place to start is to check if you underwatered your plant.

So water your plant slowly if dry allowing the water to seep into the soil to reach the roots gradually.

III. Uses and Benefits

Butterfly bush ‘Black Knight’ is perfect for shrub borders, foundation plantings, butterfly gardens, or cottage gardens.

IV. Harvesting and Storage

Butterfly bush ‘Black Knight’ can be used as cut flowers. It has a honey-like fragrance. Cutting the flowers also encourages the plant to produce more blossoms.