(Editor's Note: This article was originally published on August 25, 2010. Your comments are welcome, but please be aware that authors of previously published articles may not be able to respond to your questions.)
Buddleia (also spelled Buddleja) has the distinction of being almost impossible to kill! For gardeners in some parts of the world, this beautiful woody perennial is considered invasive. Perfect growing conditions and lack of attention are two reasons why the butterfly bush can get out of control. The flowers also produce seeds that, apparently, can remain dormant for many years until conditions are right for them to sprout. However, in my long experience with these shrubs here in Zone 6a, I've never found any seedlings anywhere near the four shrubs on the property. Gardeners considering Buddleia should check to see if it is considered invasive in their respective growing zones.
Something important to consider when choosing butterfly bush for your landscape is size; these shrubs can grow to over eight feet and spread six to seven feet. Blooms begin in July on panicles that are 5 to 6 inches long; the tiny flowers open from the base upward toward the tip. A happy Buddleia will provide a lush, lovely privacy screen all season long, and pinching back or deadheading will stimulate even more blooms through the first frost.
Buddleia species number about 100, and are a genus of the figwort family (Scrophulariaceae). They are native to warm parts of the world. Most of the varieties available today are hybrids of Buddleia davidii and include a wide range of colors, including a bicolor called, of all things, Buddleia 'Bicolor'! These blooms are not flowers made up of two colors, rather they are two different colored flowers on one inflorescence.
Butterfly bushes are very tolerant of both drought and wet conditions (although I haven't had any experience with rain for several months, so can't test that theory!). My soil is heavy clay in some places and sandy clay in others. Shrubs in both soil types have done very well, seeming to adapt to whatever conditions they have. Buddleia seems immune to insect pests, although new shoots in the spring are attractive to slugs; however, that doesn't seem to keep the shrub from growing. The biggest plus for this beauty is deer resistance; it is a good choice for properties which have a high concentration of deer during the season.
The one thing this shrub must have is full sun. I recently planted a new one in a new garden, placing it between some sea holly plants. It is in good condition and continues to bloom, but has not made any upward progress due to the shade of the two tall perennials on either side. Choose your site carefully, as these shrubs do not appreciate transplanting once established. (And they produce deep thick roots that are impossible to dig without damaging. Trust me. I've tried.)
In early spring, cut back mature shrubs to one-third of the original height. I go further than that with my two oldest plants which have reached over 9 feet the past two years; in late March, I prune the stalks to about 15 inches and by late April, the new growth measures at least 12 inches. So don't be afraid to prune.
Here is a list of some of the most popular varieties of Butterfly Bush, with flower color, growing zone, and maximum height by width.
B. davidii 'Adonis Blue'. Zones 5 to 10, blue flowers, 60 inches tall and wide
B. davidii 'Black Knight'. Zones 5 to 10, dark purple flowers, 72 inches by 48 inches (Photo 1)
B. davidii 'Butterfly Heaven'. Zones 5 to 10, lilac purple flowers, 72 inches by 60 inches
B. davidii 'Butterfly Hybrids'. Zones 5 to 10, mixed color flowers, 50 inches by 60 inches
B. davidii 'Dartmoor'. Zones 5 to 10, deep purple flowers, 72 inches by 48 inches
B. davidii 'Harlequin'. Zones 5 to 10, red flowers, 72 inches by 48 inches
B. davidii 'Ile de France'. Zones 5 to 10, purple flowers, 120 inches by 84 inches
B. davidii 'Nanho Alba'. Zones 5 to 10, white flowers, 60 inches by 48 inches
B. davidii 'Nanho Blue'. Zones 5 to 10, blue flowers, 60 inches by 48 inches
B. davidii 'Peacock'. Zones 5 to 10, pink flowers, 60 inches tall and wide
B. davidii 'Pink Delight'. Zones 5 to 10, pink flowers, 72 inches by 60 inches (Photo 3)
B. davidii 'Purple Butterfly'. Zones 4 to 10, purple flowers, 48 inches by 60 inches
B. davidii 'Purple Emperor'. Zones 5 to 10, purple flowers, 60 inches by 60 inches
B. davidii 'Royal Red'. Zones 5 to 10, purple-red flowers, 72 inches by 48 inches
B. davidii 'White Ball'. Zones 5 to 10, white flower, 72 inches by 48 inches
B. davidii 'White Profusion'. Zones 5 to 10, white flower, 72 inches by 60 inches
Buddleia 'Attraction'. Zones 5 to 10, almost red flowers, 72 inches by 60 inches
Buddleia 'Bicolor'. Zones 5 to 10, lavender and yellow flowers, 96 inches tall and wide
Buddleia 'Miss Ruby'. Zones 5 to 10, pink flowers, 60 inches by 48 inches
Buddleia 'Santana'. Zones 5 to 10, purple-red flowers, variegated leaves, 84 inches by 72 inches
Buddleia 'Silver Frost'. Zones 5 to 10, white flowers, silvery foliage, 72 inches by 60 inches
Buddleia x weyeriana 'Sungold'. Zones 5 to 10, butterscotch yellow flower, 14 feet by 12 feet (Photo 2 and thumbnail)
Buddleia x weyeriana 'Honeycomb'. Zones 5 to 10, pink flower, 18 feet tall and wide
Credit: List of Buddleia varieties created from information on http://www.daytonnursery.com