Botanical Name: Verbena bonariensis L.
Synonyms: Verbena patagonica Gillies & Hook. ex Hook.
Family: Verbenaceae
Common names: Purpletop vervain, Tall verbena, Argentinian vervain
Plant type: Short-lived perennial (self-seeds freely)
Height & Spread: 1.2–2 m × 30–45 cm
Habit: Tall, airy, see-through stems with clusters of purple flowers
Native Range & Habitat
Native to subtropical South America (Brazil, Argentina, Uruguay, Paraguay). Found in grasslands, disturbed ground, and open woodland edges. Prefers full sun and well-drained soils in the wild.
Planting & Position
- Light: Full sun is essential for sturdy stems and prolonged flowering.
- Soil: Moderately fertile, well-drained, pH 6.0–7.5.
- Spacing: 45–60 cm apart.
Botanical Description
Erect, quadrangular stems; opposite lanceolate leaves, rough to touch. Terminal, branched inflorescences bearing clusters of small lilac-purple, five-lobed flowers. Fruits are schizocarps with four nutlets.
Seasonal Interest
- Flowering period (UK): June–October
- Wildlife: Attracts bees, butterflies, and hoverflies.
- Winter: Dried seed heads add structure and feed birds.
Watering
- Establishment: Keep evenly moist during the first season.
- Established plants: Drought-tolerant — water only in prolonged dry spells.
Feeding
- Low feeding needs — a light application of balanced fertiliser in spring.
- Overfeeding can cause leggy growth.
Maintenance & Pruning
- Leave stems standing over winter for frost protection and habitat.
- Cut back to ground level in early spring before new shoots appear.
- Self-seeds readily — deadhead if control is needed.
Winter Care
- Hardy to –5 °C; mulch crowns in frost-prone areas.
- Young plants are less frost-hardy than established clumps.
Pests & Problems
- Generally pest-free.
- Powdery mildew possible in hot, dry, stagnant air — improve ventilation.
Garden Uses & Companions
Perfect for naturalistic, prairie-style, or wildlife gardens.
- Companions: Echinacea purpurea, Rudbeckia fulgida, Gaura lindheimeri, ornamental grasses (Miscanthus, Panicum).
- Excellent cut flower; long vase life.
Quick UK Care Calendar
| Month | Task |
|---|---|
| Feb–Mar | Sow indoors (18–21 °C); germinates in 2–4 weeks |
| Apr–May | Harden off, plant out after frost |
| Jun–Oct | Flowering, water if dry, deadhead if controlling seedlings |
| Nov–Feb | Leave stems for winter interest |
| Mar | Cut back to ground, mulch in cold areas |
Propagation
By Seed (most common)
- Sowing time (UK): February–March indoors, or April outdoors in mild areas.
- Method:
- Fill trays or modules with fine seed compost.
- Sow on the surface — Verbena bonariensis needs light to germinate.
- Press gently into the compost but do not cover.
- Mist lightly to settle the seeds.
- Maintain 18–21 °C; germination takes 14–28 days.
- Prick out seedlings into individual pots when large enough to handle.
- Harden off before planting out after frost risk has passed.
- Self-Seeding
- Plants readily self-sow; seedlings often appear around the parent in spring.
- Thin or transplant seedlings to prevent overcrowding.
- To encourage reseeding, leave some flower heads to mature and drop seed in autumn.
By Cuttings (less common but useful for identical clones)
- In spring, take basal cuttings from new shoots 5–7 cm long.
- Remove lower leaves, insert into free-draining compost with added grit.
- Keep in a propagator or under a clear cover at 18–20 °C until rooted.
- Pot on and grow until ready for planting out.
Award
- RHS Award of Garden Merit (AGM) — recognised for reliability and garden performance.
Top Tips for Success
- Plant in full sun for best flowering and sturdy growth.
- Let it mingle through borders for a natural, airy look.
- Leave some seed heads for self-seeding — but be ready to thin seedlings.