A lovely, under-utilized flower for midsummer through fall is purpletop vervain, or verbena bonariensis, often called simply verbena. This tender perennial is native to South America, sometimes erroneously called Brazilian vervain (a different plant entirely). ‘Bonariensis’ derives from Buenos Aires, but this plant is native to all warm areas of the southern continent from Columbia to Chile, Brazil, and Argentina.
Similar species
When we hear the word verbena, what comes to mind first are the bright annual or trailing verbenas (Glandula x hybrida) used extensively in hanging baskets and pots. There are also low-growing moss verbenas. Hoary or blue vervain (Verbena hastata) is a wildflower native to the central US, a nice choice for native meadows.
Here, I’m only discussing the tender perennial verbena bonariensis. While ‘vervain’ and ‘verbena’ are used interchangeably in the US, I’ll refer to it below as verbena or just bonariensis, to be as clear as possible. A rating chart follows.
Description
Individual verbena plants are airy, tall, sparsely-leaved and slim, commonly reaching 4 – 5 feet and occasionally taller. Wiry stems bear tufts of rosy-lavender florets at their tips, which are irresistible to butterflies. The neat, lanceolate, toothed leaves are spaced far apart in opposing pairs along the square stems, so it’s never thuggish or smothering. These plants weave easily among their companions and never need staking. I find they are effortless to care for.
Placement
Bonariensis need not be relegated to the back just because of its height; in fact, its best quality is the ability to create a see-through layer of color in the mid-border. Because it’s so slender it fits in anywhere. I love how its cool hue coordinates with or compliments everything else, knitting disparate colors together. The unique form is welcome, too. Good companions include helenium, asters, cleome, tiger lilies, agastache, Queen Anne’s lace, foxgloves and fall anemones, just to name a few.
Perhaps bonariensis’s most endearing quality is how well it attracts butterflies all season long. Pollinators can’t leave it alone. When nearly everything else but the asters are over, this plant continues to provide nectar to the last stragglers of the season. I’ve even seen hummingbirds poking it when they’re tanking up for fall migration. It looks equally at home in a meadow or informal border, as long as it gets at least 6 hours of sun a day.
Culture
Nothing could be easier to grow. While verbena bonariensis is not hardy to zone 6, it self-seeds readily if not deadheaded, and isn’t particular about soil. I let mine self-seed in fall with abandon (foregoing mulch for best germination). Then I weed out any unwanted volunteers in the spring. Seedlings are distinctive and easy to identify. Once up, verbena grows quite fast and will start blooming in July. The only affliction they get is the occasional bout of mildew, but I’ve found that is rarely a problem. They are otherwise disease-free, and pests don’t bother them.
Like other verbenas, bonariensis is appreciated for its drought tolerance, and it does well in xeric landscapes. However, it needs good moisture and well-drained soil to get started. It can be little slow to germinate in wet springs. Humidity and heavy rain doesn’t do much except spur more growth. At season’s end, just pull them out during your regular garden cleanup. If the flowers weren’t deadheaded, the seeds will have already sown, already in the ground for next spring. That’s it! So easy.
New hybrid ‘Lollipop’? Not so much
In 2020, a shorter hybrid of this plant came widely available called ‘Lollipop’. It has the same flower form in a slightly paler shade of lavender, averaging just 2 feet tall. So I tried it last year, hoping to use it in the front of the border.
I was quite disappointed. Growth was not very vigorous, it mildewed quickly and the blooms were lackluster. Because it’s so much shorter, it completely lost the charming veil-like quality of its taller cousin. Butterflies ignored it. Perhaps others have had better luck, but I can’t recommend Lollipop based on this experience. After all, not every introduction is “new and improved”. I’ll stick with the original.
In the photo below, airy bonariensis on the right balances agastache’s vertical form in the foreground. Behind, it helps make white and magenta cleome pop – a pretty contribution to the September garden!
I hope you give verbena bonariensis a try. If you can’t find it for sale at a local nursery, both seeds and plants are available via mail order. Sow a packet of seeds now for a season of color next year.
