Our Buddleia davidii bloom most of the year from late spring onwards. Of Chinese origin, quite common here in Japan.
The article below says a lot about the bush.
Buddleia: Butterfly Bush Extraordinaire
by Claire Hagen Dole
From Number 12, Spring 1997
With a name like butterfly bush, you might expect a plant to be attractive to butterflies. In fact, it’s more than attractive; it’s a magnet for all the butterflies who pass through your garden seeking nectar. Many butterfly gardeners plan their garden around Buddleia (pronounced BUD-lee-ah), a genus that includes over 100 species and cultivars. Also called summer lilac, the medium- to large-sized shrubs can anchor a perennial bed or form a hedge.
You’ll be happier with Buddleia if you accept its growth habit, which is not neat and tidy. Its narrow branches support lilac-like clusters of blossoms a foot or two in length, with side branches and blossoms. After a rainfall, the flower-laden branches of some species can droop all over your flower bed. You’ll want to allow at least six feet between bushes to keep some semblance of neatness.
But wait till you see the bush covered with fritillaries and tortoiseshells! Even a large swallowtail can land on the cluster, to sip from the many individual blooms.
Butterflies and bees will flock to the honey-scented blossoms, whose dilute nectar is sweetest in midday sun. Near a path or patio, the shrub provides delightful fragrance for you, too.
Do butterflies prefer certain colors of Buddleia? In my garden, Western Tiger Swallowtails visited all varieties (white and various shades of purple/pink/red). But Red Admirals preferred the white Buddleia while it was in bloom. Gardeners in other parts of the country may notice other preferences, if any.
History of the Butterfly Bush
Where did the name Buddleia come from? A seventeenth-century amateur botanist named Reverend Adam Buddle was honored posthumously, when the first butterfly bush reached England in 1774. Though most of today’s offerings have Chinese ancestors, this shrub (Buddleia globosa) came from Chile. Its unfamiliar name prompted one nursery tradesman to call it the “Globose Buddlebush.” Fortunately, the name didn’t stick, but common names like Chilean orange ball tree aren’t much better. It’s more precise to call it what it is: Buddleia globosa.
Victorian-era explorers brought all kinds of exotic plants back to England. From China came seeds of Buddleia davidii, the hardy species that is most familiar to gardeners today. Named after a French Jesuit missionary, Pere Armand David, B. davidii reached London’s Kew Gardens in 1896. Today, nurseries continue to develop new cultivars, like ‘Raspberry Wine’ (Carroll Gardens) and ‘Twilight’ (Mountain Valley Growers).
And horticulturists are still combing the Himalayan foothills for as-yet undiscovered Buddleia varieties. Heronswood Nursery lists three acquisitions from recent expeditions to China and Sikkim: new specimens of B. colvilei, B. fallowiana, and an unverified species (feel adventurous?).
Easy to Grow
Another reason for Buddleia’s popularity is that it’s easy to grow, even hard to kill. After one of my bushes was flattened by a windstorm, it was pruned and uprighted with little fuss. Buddleia davidii tolerates urban pollution and alkaline soil. It’s generally pest-free, except for spider mite infestations during drought or stress. It performs adequately in spare soil but prefers a sunny spot with well-drained soil, a light application of fertilizer in spring, and a few deep waterings in summer.
Spanning the Seasons
Some Buddleia species, like B. alternifolia, B. asiatica, B. colvilei and B. globosa, bloom on last year’s wood. They provide nectar for spring and early-summer butterflies, and they shouldn’t be pruned until after blossoming. In mild climates, cut back right after blooming for a second show in fall. Prune these bushes judiciously in fall, to maintain shape and remove old, woody stalks.
Among the many other varieties of Buddleia which bloom on new growth, it’s possible to stagger bloom times for a continuous nectar supply. Deadheading (cutting off) spent blossoms will force the plant to keep blooming, in an attempt to produce seed. My Buddleia ‘Lochinch,’ kept in bloom well into October, brought a Red Admiral into my garden when I’d given up seeing another.
In cold climates, mulch in the fall. Cut back to about a foot high in late winter, before new growth appears. You’ll be amazed by the height the shrub attains by midsummer. You’ll also get larger flowers and a neater-looking shape.
Hummers and Crawlers
Red-flowering varieties like B. davidii ‘Royal Red’ will attract hummingbirds, who supplement their nectar diet with protein-rich insects on the bush. Watch for other birds, like bushtits and orioles, seeking an insect meal.
An occasional butterfly chooses Buddleia as a host plant; the Western Checkerspot is the only species listed in the host plant index of James A. Scott’s The Butterflies of North America. Butterfly gardeners in northern California report seeing Buckeye caterpillars on Buddleia alternifolia and Echo Blue butterflies laying eggs on Buddleia ‘Lochinch.’
Read the rest of the article here.
Reprint permission pending.