The purpletop vervain is a delicate and worth seeing companion in the bed. In summer, it has its big appearance and inspires with great possibilities of combination. Here are some tips on sowing, planting and caring for this short-lived perennial.
Profile of purpletop vervain:
Scientific name: Verbena bonariensis
Plant family: verbena family (Verbenaceae)
Other names: clustertop vervain, Argentinian vervain, tall verbena, pretty verbena
Sowing time: autumn
Planting time: spring
Flowering period: July to October
Soil quality: sandy to loamy, nutrient rich, humus rich
These information are for temperate climate!
Use in: flowerbeds, bouquets, group planting, planters, rose companion, borders, cottage garden, flower garden, natural garden, prairie garden, potted garden
Winter hardiness: hardy, USDA Plant Hardiness Zones: 8 (-10 °C / +15 °F)
Bee and insect friendly: Yes
Plant characteristics and classification of purpletop vervain
Plant order, origin and occurrence of purpletop vervain
The purpletop vervain (Verbena bonariensis) belongs to the genus Verbena, which comprises more than 250 species. This verbena is a perennial originating from South America, but in our latitudes it is not sufficiently hardy and therefore rather short-lived. Therefore it is often used as a summer flower – even though it can grow in the garden for years by self-sowing.
Purpletop vervain owes its botanical species name ‘bonariensis’ to the fact that it was first discovered by Europeans in the Argentine capital Buenos Aires. For this reason it is often called Argentinian vervain. Like all verbenas, Verbena bonariensis belongs to the verbena family (Verbenaceae).
Characteristics of purpletop vervain
Purpletop vervain grows erect and appears somewhat spindly due to its long, bare stems with terminal flowers. Even though it appears rather filigree at first glance, the stems are very strong and reach growth heights of up to 2 meters (80 in).
The green leaves stand very far apart on the stem, which gives the plant an airy appearance. They are arranged in pairs in opposite directions, sessile, about 13 centimeters (5.2 in) long, lanceolate and toothed towards the tip.
Purpletop vervain carries flat, up to 5 centimeters (2 in) wide violet cyme on the stem ends. They consist of many star-shaped individual flowers of a maximum size of 6 millimeters (0.24 in). The first flowers open already in July and then remain until the first frosts. The plant is equally popular with bees and butterflies.
After flowering, purpletop vervain forms small seeds, through which it survives by self-seeding.
Purpletop vervain – cultivation and care
The purpletop vervain prefers a full sunny location. Due to its low winter hardiness it survives winter only with an appropriate protection. But even if the mother plant should freeze to death, it provides for sufficient offspring by self-sowing.
Purpletop vervain thrives on nutrient-rich, sandy-humic and permeable soils, which should be as dry as possible, especially in winter, because like most steppe plants the verbena reacts quite sensitively to winter wetness.
The best time of year to sow the purpletop vervain is autumn, because the seeds need a cold stimulus to germinate. If you want to grow the perennial from seeds, it is best to do this in November. The sowing can be done directly in the field. The seeds should be thinly covered with soil and kept well moist during the first few weeks. Alternatively, you can also prefer to plant Verbena bonariensis from February on the windowsill or in the greenhouse, in order to plant it out in spring in specific places in the bed. The seeds grow at a temperature of 18 to 22 °C / 64 ot 72 °F within 14 to 20 days.
Planting purpletop vervain
Since purpletop vervain is only conditionally hardy, it should be planted in spring so that it can grow well until winter.
The plant is very easy to care for in the right place. If you want it to stay in the bed by self-sowing, you should leave the withered stems until spring. Otherwise, you can cut the plant back to about 20 centimeters (8 in) above the ground. In the spring, the dried stalk remains are then removed once again.
Purpletop vervain is one of the short-lived perennials, but it ensures its survival in the bed by self-sowing – and that without getting out of control. If this is desired, you should leave the flower heads until spring so that the plants can be seeded. Also, be careful not to confuse the seedlings with unwanted wild herbs in spring. Wait until the foliage is clearly visible.
Diseases and pests
Occasionally an infestation with powdery mildew can occur. A far greater problem for purpletop vervain is waterlogging, as it can quickly lead to root rot. Therefore, before planting in heavy, loamy soils, work in some sand to loosen them up.
Purpletop vervain is hardy down to -10 °C / +15 °F. In order for the frost-sensitive plant to survive winter, it needs a protective cover of fir brushwood and autumn leaves.
Use in the garden
At the latest since the trend of prairie beds purpletop vervain must not be missing in any planting: Airy and light, the small, densely filled, purple flower umbels dance over the bed partners and gently surround them. The tall plant is an ideal structure builder and brings balance to the bed. It is particularly popular because of its sparse growth and its slightly unruly appearance. Combined with foxglove, Lindheimer’s beeblossom (Gaura lindheimeri) or Jerusalem sage (Phlomis) it attracts all eyes. The big advantage of purpletop vervain: It has a very open growth, i.e. the stems are mostly leafless and allow a view of the flowering of the other plants in the bed. Above them the violet flower umbels seem to float and set pretty accents. Great partners are, for example, coneflower (Rudbeckia), common sneezeweed (Helenium) or tickseed (Coreopsis), whose bright flowers form a beautiful contrast to the purple flower umbels of verbena.
purpletop vervain has a variety called ‘Lollipop’, which is often called the “little sister” of the species: With a growth height between 50 and 60 centimeters (20 and 24 in), it remains significantly smaller than the species, otherwise there are no significant differences.