Argentinian Vervain
Sacred sprig from Buenos Aires
The Argentinian Vervain comes from the tropical parts of South America. Vervain or Verbena means ‘sacred twig’. It got its name because the flower sprigs were used in rituals. The second name ‘bonariensis’ marks the link to Buenos Aires, the capital of Argentina. It was from there that seeds were sent to Europe in the early 18th century. Today, the giant verbena is a common sight in plantings, especially appreciated for its delicate flowers and tall silhouette.
Cold snap helps the seeds to germinate
Giant hogweed seeds germinate best when they are stratified, i.e. cold treated. Sometimes we get seedlings when sowing indoors without any cold treatment at all. So it’s worth trying! But if no seeds have emerged after about 3 weeks, then it is time to use the cold method. Here are two ways to stratify the seeds:
- Sow outdoors in autumn
Sow in Oct-Nov. Scatter the seeds sparsely in a pot or outdoors. Argentinian Vervain seeds are light-growing. Therefore, cover them only lightly with sowing soil. The seedlings will emerge the following spring.
- Sow indoors in spring-winter
Sow in January-March. Sprinkle the seeds sparsely in the growing container. The seeds of the Argentinian vervain are light-growing. Therefore, cover them only lightly with sowing soil. Place the seeds outdoors or in the refrigerator for 2-4 weeks. Then bring the pot back into the warmth. Now the seeds are ready to germinate at a temperature of 15-20 degrees.
Easy to take cuttings
When the Argentinian vervain has developed a few leaves, give each one a pot. When they have grown for a while in their own pot, prune them. This will make the plants strong and well-branched. Cut just above a leaf. The cut shoot can be planted in moist soil and become an independent plant.
Argentinian vervain outdoors
Plant out when the risk of frost is over. Harden off the giant vervain for a few days by leaving it outside for longer and longer periods. Choose a sunny or semi-shady spot.
Each plant will branch out and grow many stems. Therefore, give the giant vervain some space, about 50 cm between plants.
The light purple flowers appear in July. Or already in June if sown early. Because giant vervain grows to over a metre in height and the flowers are at the top, it makes an excellent background plant in a bed. It also looks great planted with ornamental grasses.
Water and fertilise regularly. The giant vervain is a problem-free plant that is usually free of diseases and pests.
In our garden, we like to have something that blooms throughout the season. Argentinian vervain is one of those brave plants that saves the day in late autumn. It carelessly keeps on flowering when the cold nights make many other summer flowers give up.
Argentinian giant vervain in a pot
Argentinian vervain is really nice to grow in a pot. Feel free to put leca balls in the bottom, because it doesn’t like to stand with its roots soaking wet. But remember to water regularly – especially if you use a clay pot. Clay is a breathable material and therefore releases more water than plastic.
Overwintering giant vervain
In southern Sweden, Argentinian vervain can be overwintered. Cover the plant with straw or leaves to increase the chances of it coming to life when spring arrives.
In the rest of the country, Argentinian vervain can be overwintered indoors, much like geraniums. Cut back the stems so that about 10cm is left. Store the roots in seed soil or sand. A pot-grown plant can easily be cut back and brought indoors. Leave it frost-free during the winter. When the sun comes out in the spring, it’s time to water and feed it again. The plant now has sturdy roots and gets a jump start on growth and flowering.
Author: Johanna Damm
Fact-checked by Erik Hoekstra
Last updated 2022-10-14