Butterfly Bush Plants: Magnet for Swallowtails, Controversy

Buddleia Lives Up to Its Common Name

Image of a monarch on a butterfly bush flower.
A monarch enjoying a butterfly bush flower. David Beaulieu

Plant taxonomy classifies butterfly bush as Buddleja davidii, more commonly given as Buddleia davidii. It is often treated by gardeners as a perennial flower, but, botanically speaking, is considered a shrub. This plant is a magnet for swallowtails and other butterflies, but also for controversy.

Characteristics of Butterfly Bush Plants:

There are many cultivars of butterfly bush, and exact plant characteristics will vary from cultivar to cultivar.

Growing conditions will also have an impact on the plant's mature size. The species plant will grow to be 6-12 feet tall and have a spread of 4-15 feet, but the cultivars generally stay smaller than that.

Blooms on these shrubs develop in clusters on floppy panicles and can be purple, pink, white, or red in color, and they often have an orange "throat" in the center. The shrubs will bloom throughout the summer if deadheaded. Leaves are lance-shaped and grayish-green on their undersides. They are fast-growing shrubs with arching branches.

The climate is most favorable for growing this specimen in USDA planting zones 5-10. It is native to China, and it is with this fact that the story of the plant's controversial status begins.

That's because butterfly bush is considered invasive in many areas of the United States. Check with your local county extension to learn whether or not it's invasive where you live.

If it's not listed as invasive in your area but you're still worried that it might spread, confine the plant within the bounds of your garden by deadheading, since this shrub spreads via seed. Alternatively, grow a native shrub as a substitute (see below).

Butterfly bush is particularly adept at attracting tiger swallowtails and monarchs (see picture).

But this nectar plant also attracts hummingbirds, making it a tempting addition to hummingbird gardens, too. And don't forget the bees: the shrub will also attract the bees that will pollinate other plants in your garden. Fortunately, they are rabbit-proof flowers.

Care, Growing Conditions, Uses for Butterfly Bush Plants:

Apply garden mulch around your plants in the fall, then prune them back to the ground in late winter. This plant will re-emerge from its roots in spring. Butterfly bush flowers on new wood (new growth). Pruning tends to improve blooming, giving you incentive to prune it. You essentially want to treat butterfly bush plant as if it were an herbaceous perennial rather than a shrub.

This is a plant for full sun, and it needs a well-drained soil. It is a relatively drought-tolerant shrub.

Even those who don't care about attracting wildlife often use butterfly bush plant for aesthetic purposes. As a tall plant, it is a good choice for the back row of a perennial border. To achieve maximum visual appeal, mass plantings of butterfly bush together. The natural unruliness of the plant lends itself to use in "cottage gardens."

Controversy -- The Question of the Invasive Nature of Butterfly Bush Plants:

As stated above, the species plant, Buddleia davidii, is invasive in some regions of North America -- a serious point that demands clear-headed, dispassionate, rational debate.

We must not throw every argument in the book out there, hoping that they all stick and, as a result, make our case stronger. On the contrary, intermingling weaker arguments with the strongest argument only diminishes the cogency of the latter by muddying the waters. So allow me a few observations:

  1. The strongest argument to be made against growing butterfly bush is that the species plant (Buddleia davidii) is definitely invasive in some regions. Period. In addition, it may possibly become invasive even in other regions in the future. Furthermore, allegedly non-invasive sterile cultivars such as 'Blue Chip' butterfly bush may not turn out to be the solution to the problem, since other plants touted as "safe" sterile cultivars in the past have turned out to be disappointing in this regard.
  2. A weaker argument that has become popular is, "While it's a good source of nectar for butterflies, caterpillars don't feed on its leaves, so it's not a legitimate food plant." This may be true, as far as it goes, but it's an excessively narrow perspective. The crux of the matter is still the invasive nature of the plant. If it were to turn out that the 'Blue Chip' cultivar is truly non-invasive, there would be no reason why I shouldn't grow it, as long as I also grow "legitimate" food plants such as common milkweed. I can, after all, grow both. It's not an all-or-nothing proposition.  
  1. You will also hear an argument built on #2 that runs something like this: "Because caterpillars don't eat the leaves, it does nothing for the ecosystem, so it's useless -- basically just a guilty pleasure." OK, call me decadent, but I submit that life would not be worth living without guilty pleasures such as a love for beautiful paintings, poetry, gourmet food -- and, yes, plants that serve no function other than to delight my senses. Ascetic arguments of this sort only serve to turn off many of us. Stick to your strongest argument, folks!

If you're an activist on this issue, I challenge you to a thought experiment. I'm going to ask you to put a few questions to yourself. How you answer the questions will determine whether your main interest is in stopping the growing of invasive plants or is, instead, in limiting plant selection strictly to native plants. Here's the question: if it were eventually proven that 'Blue Chip' was, indeed, a non-invasive cultivar, would you be happy upon hearing the news? Would you rejoice that another choice had been introduced into the arena? Would you at least be mildly comforted that you could now (however reluctantly) suggest a non-invasive butterfly bush to those who feel they absolutely must grown one? Or would you be annoyed that the debate had just become more complicated?

It would be convenient if everyone found the native alternatives to butterfly bush equally beautiful, but let's not kid ourselves. We're faced with an inconvenient truth: everyone's tastes are different, and some people will not find the natives usually mentioned in this context to be as beautiful as what they would replace. We can ask them to avoid growing butterfly bush and, instead, grow the native plants, anyway, but we shouldn't be arrogant about it and smugly pretend that we're not asking gardeners to settle for what are, in their own minds, poor substitutes. It's important to be honest, rather than glossing over reality. So let me speak for myself -- and only for myself: I, personally, happen to prefer some native alternatives:

Native Alternatives and Final Thoughts:

Plants native to my region that are host plants (i.e., plants that caterpillars eat) include:

  1. Pussy willow
  2. New England aster
  3. Mountain laurel

Don't confuse butterfly bush plants (Buddleia davidii) with butterfly weed (Asclepias tuberosa). Butterfly weed is a type of milkweed and serves as a host for the caterpillars of monarch butterflies. Adult tiger swallowtails and black swallowtails enjoy its nectar. Both perennials are sometimes referred to simply as "the butterfly plant." They are, however, unrelated.

Buddleia davidii 'Black Knight' is one of the most popular cultivars of butterfly bush. Its purple blooms are so dark as to be almost black flowers.

For more, see Plants That Attract Butterflies.