Updated: Jul 21, 2021
Meet my buddy, David. That might be a way to remember the Latin name, but it can also be called by its common name, butterfly bush. Butterflies do indeed take advantage of its nectar; shown below is a monarch on one such shrub. Buddleja davidii has been a favorite pollinator plant for sometime, but unfortunately there are concerns about invasiveness. Currently, the California Invasive Plant Council lists B. davidii as one to watch in California, because the northwest has experienced reseeding in mild areas. The Jepson Herbarium, however, has reported and mapped where several have been found, including within the Bay Area. I have not seen reseeding locally, but that may be due to our dry conditions or location. For now, butterfly bush is still available at most nurseries, and planted in the right location, the joyous flowers and proper maintenance might outweigh the concern.
I do wonder if the cultivars are as concerning than the species. If I find out I will pass on the information. There are numerous cultivars varying in color and shrub size, even leaf variegation, which will accommodate different design criteria. Dwarfs can be used in containers, whereas larger cultivars are well suited at the back of a flowering border. The specimen with the yellowing leaves (shown below) does not ever receive adequate moisture to thrive, but it still is a prolific bloomer. Next spring, it should receive a hard pruning, as Sunset recommends, then see what happens. I will include a healthy example from the internet for comparison.
Botanical Name: Buddleja davidii
Buddleja: Honoree, botanist and cleric Adam Buddle
Davidii: Honoree, naturalist and missionary Père Armand David
Common Name: Butterfly bush
Family Name: Scrophulariaceae
Origin: East Asia
Positioning: Coastal, lawn edge, slopes, background (for larger specimens)
Garden Themes: Pollinator/hummingbird, drought/Mediterranean, cottage/informal
Uses: Border, mass, specimen, informal hedge, cut flower
Type: Evergreen to semi-evergreen shrub
Form: Upright, vase to arching vase
Size: 5' (dwarf cultivars) to 15' tall and wide
Outstanding Feature(s): Flower
Bark: Medium gray
Color: Silver, gray, gray green above, lighter underneath
Surface: Lightly hairy
Flower: Summer into autumn. Terminal and axial panicles of small, light lavender blue, and tubular. Cultivars may be white, pink, shades of purple, blue, magenta, and yellow. Slightly fragrant.
cultural requirements, tolerances & problems
Sunset Zones: 2-24; H1
USDA Zones: 5-9
Light: Full sun
WUCOLS SF Bay Area Hydro Zone: Moderate
Texture: Sand, loam, clay, rocky (well-drained and well composted)
Moisture Retention: May dry between watering
Tolerances: Drought, heat, deer
Problems: May become floppy with too much water and/or too little sun; considered invasive
Insects: Spider mites
citations & attributions
Bayton, R. (2019). The Royal Horticultural Society's the Gardener's Botanical: An Encyclopedia of Latin Plant Names. London: Mitchell Beazley.
Missouri Botanical Garden. "Buddleja davidii 'Black Knight'." Accessed on July 11, 2021 from https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=b750.
NC State Extension. "Buddleja davidii." North Carolina State University, Raleigh. Accessed on July 11, 2021 from https://plants.ces.ncsu.edu/plants/buddleja-davidii/.
Norris Brenzel, K. (Ed.). (2012). The New Sunset Western Garden Book. New York: Time Home Entertainment, Inc.
Water Use Classification of Landscape Species. "WUCOLS IV Plant List." University of California, Division of Agriculture and Natural Resources, Davis. Accessed on June 28, 2021 from https://ucanr.edu/sites/WUCOLS/Download_WUCOLS_IV_List/.