Updated: Nov 22, 2021
Unlike most perennials, Verbena bonariensis provides a unique texture and height in a border garden. Rigidly upright and topped with clusters and very small flowers, its peak bloom is quite showy for a long period. If I can be truly candid here, I have only been successful designing with and growing two Verbenas: V. bonariensis and the very similar blooming but different growth habit, V. rigida. For the latter, it would be understandable if the name leads to confusion, since rigida implies stiffness, which perfectly describes the erect form of the former. Bonariensis tells us nothing about its form but a reference to its origin, Buenos Aires, yet both are native to South America, including Argentina, so...interesting but not helpful. If one were to close-clip the flowers from both, it would be difficult to distinguish the two with untrained eyes.
For landscape design, the main distinction is their form. In full bloom, V. rigida is no more than 2' tall and can reach 4' wide, behaving as a loose mound. V. bonariensis will reach a height of 6' but only half as wide. Where we can further experience confusion, unfortunately, is a newer cultivar, V. bonariensis 'Lollipop' (last two photos below) maintains a more upright form but is the size of V. rigida, about 2' tall by 3' wide. Have I lost you in the comparisons? Let's look at some similarities and concerns.
All three plants are loved by butterflies, are drought tolerant, and share a propensity for a long, showy, summer bloom period. Only V. bonariensis is on California Invasive Plant Council's watch list for readily reseeding, and I can attest to this nature in my own garden. Fortunately, their offspring have not been that strong; while drought tolerant, sprouting up in areas with no water leads to a slow withering decline. This tells me that V. bonariensis is still worthy of specifying in gardens, but location, location, location! It may be more suited for urban gardens over rural edge where there may be a risk of escape.
I started this post by referencing its texture and height as a desirable element in a perennial border. The first photo below attests to its unique qualities, providing an almost ethereal presence when planted in masses. A single plant works well, too, lending contrast with lower, perhaps broadleaf perennials. V. bonariensis compliments informal designs, but I think that informality could take on modern forms as well as traditional cottage garden styles.
Tom Attwood is a garden designer in the United Kingdom that shares great footage of V. bonariensis being visited by their native butterflies.
Botanical Name: Verbena bonariensis
Verbena: Latin for sacred bough, however the reference may not be linked to the species we know today.
Bonariensis: Buenos Aires
Common Name: No common name
Family Name: Verbenaceae
Origin: South America (Sunset adds "naturalized in California")
Positioning: Middle ground, background, drifts, silhouette, slopes
Garden Themes: Mediterranean/dry, rock, container, courtyard/patio, meadow, pollinator, cottage
Uses: Border, mass, accent, specimen, embankment cover
Type: Herbaceous perennial
Form: Clump, erect
Size: 6' tall by 3' wide
Outstanding Feature(s): Flower, form
Stem: Green, square, tomentose
Leaf: Enters dormancy after spring rains stop.
Arrangement: Opposite with sessile attachment (no leaf stem)
Shape: Lanceolate, elliptic, oblong
Color: Dark green
Surface: Scabrous above, tomentose underneath
Flower: Summer to Autumn. Corymb (cluster) of small, purple flowers set atop a peduncle (stalk). Showy
Fruit: Autumn to Winter. Elongated nutlets with the potential to readily reseed.
cultural requirements, tolerances & problems
Sunset Zones: 8-24
USDA Zones: 7-11
WUCOLS SF Bay Area Hydro Zone: Very low
Texture: Sand, silty loam, clay, rocky
Moisture Retention: Well-drained but performs better with moisture without extended dry periods
pH: Slightly acidic to neutral
Tolerances: Drought, deer, poor soils
Problems: Reseeding, may be invasive
Branch Strength: N/A
Insects: Not recorded at time of posting.
Disease: Powdery mildew
citations & attributions
Bayton, R. (2019). The Royal Horticultural Society's the Gardener's Botanical: An Encyclopedia of Latin Plant Names. London: Mitchell Beazley.
BioNET-EAFRINET. "Verbena bonariensis (Purple Top)." Lucid Key Server, Queensland. Accessed on September 10, 2021 from https://keys.lucidcentral.org/keys/v3/eafrinet/weeds/key/weeds/Media/Html/Verbena_bonariensis_(Purple_Top).htm.
Cal-IPC Plants A to Z. "Verbena bonariensis." California Invasive Plant Council, Berkeley. Accessed on September 10, 2021, from https://www.cal-ipc.org/plants/profile/verbena-bonariensis-profile/.
Extension Gardener. "Verbena bonariensis." North Carolina State University, Raleigh. Accessed on September 10, 2021, from https://plants.ces.ncsu.edu/plants/verbena-bonariensis/.
Jepson Herbarium, Taxon Page. "Verbena bonariensis." University of California, Berkeley. Accessed on September 10, 2021, from https://ucjeps.berkeley.edu/eflora/eflora_display.php?tid=47885.
Norris Brenzel, K. (Ed.). (2012). The New Sunset Western Garden Book. New York: Time Home Entertainment, Inc.
Plant Finder. "Verbena bonariensis." Missouri Botanical Garden, St. Louis. Accessed on September 10, 2021, from http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=a111.
Water Use Classification of Landscape Species. "WUCOLS IV Plant List." University of California, Division of Agriculture and Natural Resources, Davis. Accessed on September 7, 2021.
Butterflies: "Monarch on Verbena Bonariensis" by Dwight Sipler is licensed under Creative Commons Attribution 2.0 Generic (CC BY 2.0).
Feature flower detail: "Verbena bonariensis" by Linda De Volder is licensed under Creative Commons Attribution-NonCommercial-NoDerivs 2.0 Generic (CC BY-NC-ND 2.0)
Leaf detail: "Verbena bonariensis (purpletop vervain, tall verbena), single plant in new plug bed near Hourglass Lake, likely a garden stray; stem & leaves" by Tom Potterfield is licensed under Creative Commons Attribution-NonCommercial-NoDerivs 2.0 Generic (CC BY-NC-ND 2.0).
Mass planting: "Verbena Bonariensis, Merriments gardens" by Oast House Archive is licensed under Creative Commons Attribution-NonCommercial-NoDerivs 2.0 Generic (CC BY-NC-ND 2.0)
Single plant in bloom: "Verbena bonariensis Prague 2011 1" by Karelj is licensed under Creative Commons Attribution-ShareAlike 3.0 Unported (CC BY-SA 3.0).
All other photos by TELCS.