Caren White is a Master Gardener and instructor at Home Gardeners School. She has been associated with Rutgers Gardens for over a decade.
I tend to grow the same flowers every year. Once in while, though, I find a new favorite flower. I only had to see Verbena bonariensis once to make it a mainstay in my garden. It’s perfect in a cottage garden style garden, attracts butterflies and hummingbirds and readily reseeds itself in my garden so I am never without it. It’s a winner.
What is Verbena Bonariensis?
Verbena bonariensis is a flowering perennial that is a member of the Verbena family. It is native to Argentina and Brazil. Bonariensis refers to the Argentinian capital, Buenos Aires. It is also known as Purpletop and Purpletop Vervain.
Verbena bonariensis was first grown in England in 1726 when James and William Sherard received seeds from Argentina. It was spread to the US, Australia and South Africa by English colonists. It has naturalized in all of those countries and is considered a weed in some areas because of its tendency to self-sow and its drought tolerance.
Verbena bonariensis is perennial on zones 7 – 11. In colder climates, it is grown as an annual. I garden in zone 6 and love that these plants will bloom the first year from seed unlike most perennials which do not bloom until their second year of growth.
The plants grow 3 to 6 feet tall in full sun to partial shade. They grow in almost any kind of soil. Once established, they are drought tolerant. The stems are square like many members of the mint family. The leaves are lance-shaped and set far apart on the stems giving the plants an airy feel. That airy feel is completed by the flowers. The flowers are borne in 2 inch clusters of purple flowers. Butterflies find them irresistible. Bloomtime is mid-summer through frost.
How to Grow Verbana Bonariensis
Verbena bonariensis grows in full sun to part shade. It is not fussy about soil. You do not need to do any special preparation of your soil. You do not need to fertilize at all during the growing season. I add compost to all of my gardens yearly. Adding compost, which is not as nutrient dense as commercial fertilizer, not only adds nutrients to the soil, but also helps to texturize the soil, adding drainage to heavy soils and helping sandy soil to retain moisture.
You should space your plants 2 feet apart. Since they are so light and airy looking, it is recommended that you plant them in large swathes to make them really stand out. My preference is to use them as accents in my garden, popping up in unexpected places to add spots of purple throughout my beds. You should plant them in whatever way pleases you.
If you have planted seeds and have seedlings to care for or have added plants purchased from a nursery, you will want to keep them well-watered until they become established. Once established, these plants are drought tolerant. They can tolerate long periods of dryness but do best with 1 inch of water or rainfall per week.
Verbena bonariensis will freely self-seed in your garden. My own experience is that they are a little too free with those seeds! Every spring I have several dozen seedlings to remove from places in my garden where I don’t want them to grow. There is no need for me to transplant them into other spots because there are already plenty of seedlings growing where I want new plants. Deadheading the flowers during the summer will prevent them from making seed that will produce new seedlings the following year.
How to Grow Verbena Bonariensis From Seed
Because these plants grow so readily from seed, they are very seldom sold as plants. Most gardeners grow them from seed.
You can direct sow your seeds in your garden after your last frost. Plant them about ¼ inch deep and keep them well-watered. The seeds take a while to germinate. They will germinate sporadically until June. Thin the seedlings to 2 feet apart.
You can also start your seeds indoors 6 to 8 weeks before your last frost. Plant them ¼ inch deep and keep the soil moist. Be patient. Germination will take a while and be spotty. You can transplant your seedlings into your garden after your last frost when the soil has warmed, spacing them 2 feet apart.
© 2020 Caren White