Purpletop Vervain

Verbena bonariensis is a tall, airy flowering plant reaching 100–120 cm, bearing dense clusters of small, vivid purple-violet blooms on slender, branching stems. Originally from South America, it is grown as an annual in Nordic climates, though it readily self-seeds and returns year after year. It thrives in full sun with well-drained soil and tolerates dry spells once established. An excellent cut flower and a magnet for pollinators.

Growing

Seeds require cold stratification before sowing: place damp seeds in the refrigerator for 14 days, or expose the sown tray to light frost for a few nights (not below −4 °C). Start seeds indoors 10–12 weeks before the last frost period, sowing very shallowly at just 0.2 cm depth into moist seed compost. Germination is slow — allow 3–6 weeks and maintain temperatures around 18–20 °C. Prick out seedlings when large enough to handle and pot on. Harden off transplants gradually and plant out at 35 cm spacing once nights reliably stay above 5 °C.

Care

Water moderately; established plants tolerate short dry periods but perform best with consistent moisture during flowering. Apply a balanced liquid feed every 3–4 weeks once in active growth. Deadhead regularly to extend the flowering period, or leave some flowerheads to set seed for natural self-seeding. Tall plants may need light staking in exposed positions. No pruning is required during the growing season.

Harvest

Cut stems for the vase when approximately half the florets in a cluster have opened — this maximises vase life. Use sharp scissors or snips and cut stems long, early in the day. Flowers continue until the first hard frost. For dried flowers, harvest when clusters are fully open and hang upside-down in a dry, airy space.

In the kitchen

Verbena bonariensis flowers are edible and can be used as a delicate garnish on salads, desserts, and cocktails. The tiny purple florets add colour to summer drinks and are sometimes crystallised for cake decoration. The flavour is mild and slightly herbal.

Storing

Fresh-cut stems last 7–10 days in clean water in a cool spot, changing the water every 2 days. Dried flower clusters keep for several months stored in a cool, dry, dark place in a paper bag or open box. Do not seal in airtight containers as this encourages mould.