How to grow verbena
Overview
Verbena bonariensis is a tall, clump-forming herbaceous perennial from South America, grown for its wiry stems topped with clusters of small purple flowers. It is a classic 'see-through' plant that adds vertical interest and movement to garden beds without blocking views, and is highly attractive to pollinators.
Varieties
- Verbena bonariensis 'Lollipop' — A compact dwarf form reaching 60 cm, ideal for small gardens and pots without the tall, wispy habit of the species.
- Verbena bonariensis 'Purpletop' — The standard tall form (1.2–1.5 m) with deep violet flowers, widely available in Australian nurseries.
Soil Preparation
Verbena prefers neutral to slightly alkaline soil (pH 6.5–7.5) with sharp drainage. In heavy clay, improve with coarse sand or gravel and plant on a slight mound. Add a handful of slow-release organic fertiliser at planting time, but avoid rich compost that encourages lush, floppy growth.
Growing Guide
Plant Verbena bonariensis in full sun and well-drained soil; it tolerates poor soils but rots in heavy clay. Space plants 40–50 cm apart for an airy drift or 30 cm for a denser effect. Sow seed directly on the surface in spring or early summer (do not bury, as light aids germination) or transplant seedlings after frost risk passes. In Mediterranean climates, sow in autumn for winter-spring flowering. Pinch out tips when 15 cm tall to encourage bushiness.
Sowing
Sow seed on the surface of fine, moist seed-raising mix in spring or early summer; do not cover as light is needed for germination. Seeds germinate in 14–21 days at 18–22°C. Thin seedlings to 30 cm apart. Direct sowing is reliable in warm soils, but transplanting gives a head start in cooler zones.
Care
Feed lightly with a balanced liquid fertiliser every 4–6 weeks during the growing season. Deadhead spent flower stems regularly to prolong blooming and reduce excessive self-seeding. Cut back hard to 10 cm in late autumn after flowering to maintain a compact shape and prevent woody, leggy growth.
Companion Planting
Excellent companions include Gaura, Echinacea, Salvia, and ornamental grasses like Pennisetum for texture contrast. Avoid planting near low-growing groundcovers that may be smothered, as Verbena self-seeds freely and can become weedy in crowded borders.
Common Pests & Risks
Aphids may cluster on new growth in spring; blast off with water or use a mild soap spray. Powdery mildew appears in humid, crowded conditions; improve air circulation by spacing adequately and avoid overhead watering. Red spider mite can occur in hot, dry spells.
Harvesting
Cut flower stems for fresh bouquets when the lowest florets on the cluster just begin to open; they last 7–10 days in water. For dried arrangements, harvest when most florets are open but before they shatter. Leave spent stems on the plant for winter seed heads and insect habitat.
Troubleshooting
Yellow leaves: overwatering or poor drainage — reduce watering and improve soil. Brown leaf edges: underwatering or hot, dry wind — mulch and increase watering frequency. Leggy, floppy stems: too much shade or rich soil — move to full sun and reduce feeding. Powdery mildew on leaves: poor air circulation — space plants wider and avoid overhead watering. Self-seeding becoming invasive: deadhead promptly before seeds ripen.