Q. I’ve wanted a pink-flowering butterfly bush in my yard for years. Last spring I finally found and planted a ‘Pink Delight’ butterfly bush. It grew like a weed and got way too big for the place where I planted it, so I kept cutting it back and only got a few small flowers. My questions are how far back can you cut butterfly bush without killing it, are they easy to transplant, and are there any kinds that only get four or five feet tall?
A. The first few years I lived in Central New York I hesitated to recommend this exotic-looking sub-shrub for fear that it wouldn’t survive our long, bitter winters. As it turns out, butterfly bush (Buddleia davidii) thrives as a herbaceous perennial in all but our most exposed and/or wet locations. In fact, the cultivar, ‘Pink Delight,’ that you planted happens to be my favorite butterfly bush!
In response to your specific questions let me offer the following thoughts.
First, you can cut the woody canes of butterfly bush to within four to six inches of the ground, at left. While some people prefer to do this in the fall to neaten up their garden before winter, I suggest waiting until spring so that the canes will trap and hold a layer of insulating snow around the base of the plant throughout the coldest parts of the winter.
Butterfly bush are also very easy to transplant. Just cut the canes back, dig as large of a ball of soil around the roots as manageable, then move the plant to a spot in full sun (while butterfly bush will grow in moderate shade, it won't flower well) that also has very well-drained to dry soils (butterfly bush will not survive in wet, heavy clay soils). And, as you've learned, butterfly bush needs plenty of space as most varieties can grow between six and eight feet tall in a single season!
Finally, as I just pointed out, most butterfly bush selections can become quite large. However, because of the incredible natural diversity within the genus Buddleia and because of its increasing popularity with the gardening public, an almost dizzying number of new introductions are now coming to market. Currently, the most reliably compact (though certainly not dwarf) forms are those having Buddleia davidii var. nanhoensis (say that three times fast) as a parent. These include ‘Nanho Alba,’ ‘Nanho Blue,’ ‘Nanho Purple,’ ‘Petite Indigo,’ and ‘Petite Plum’ among others. All of these cultivars will likely grow from the ground to between four to six feet tall and wide between May and September.