Purpletop vervain

Sun

Full sun; light shade is tolerated, but flowering is reduced and stems may lean.

Water

Water regularly while establishing. Once rooted, it tolerates dry spells; water during prolonged drought to maintain flowering.

Soil

Well-drained soil, including sandy, chalky or gravelly ground. Avoid winter waterlogging and heavily enriched soil.

Height

4-6 ft (1.2-1.8 m)

Spread

1-3 ft (0.3-0.9 m)

Flowers

Small violet-purple flowers in flattened clusters from summer into autumn, often until frost.

Foliage

Rough, narrow, toothed green leaves, mostly low on the plant, with smaller opposite leaves along square stems.

Growth

Fast; can flower in its first year from an early sowing.

Care needed

Low

• Water new plants through their first growing season, letting the soil surface dry between waterings.
• Avoid heavy feeding; rich soil encourages soft, floppy growth.
• In colder gardens, mulch around the crown after the ground cools, keeping wet material away from the stem bases.
• Use discreet stakes or nearby sturdy plants for support on exposed sites.
• Remove unwanted seedlings while small, and deadhead before seed ripens where spreading is a concern.

Pruning. Cut old stems back to new basal growth in early spring, once the risk of severe frost has eased. Where self-seeding is unwanted, remove faded flower heads throughout the season rather than leaving them over winter.

Late winter

Sow seed under cover for early flowering; germination can be slow and uneven.

Early spring

Cut down old stems as new basal shoots appear, delaying in areas still facing severe frost.

Spring

Remove excess self-sown seedlings or transplant a few while they are small.

Late spring

Plant out after frost, allowing about 1.5-2 ft (0.45-0.6 m) between plants.

Summer

Water during prolonged dry spells and support leaning stems if necessary.

Autumn

Remove seed heads where spread is a concern; otherwise leave some standing stems for winter structure.

Late autumn

Apply a loose mulch around the crown in colder gardens, without covering it with wet, compacted material.

• Thread through mixed borders to create a veil of purple without hiding plants behind it.
• Combine with ornamental grasses, coneflowers and black-eyed Susans for a loose, late-season planting.
• Repeat small groups along a sunny path to link separate planting areas.
• Use in well-drained gravel gardens for height above lower, drought-tolerant plants.

Garden styles it suits: New perennial (prairie), Cottage garden, Pollinator garden, Dry gravel garden, Modern and Wildlife garden.

Plant it with: Purple coneflower, Black-eyed Susan, Switchgrass, Catmint, Yarrow and Russian sage.

Wildlife: Nectar-rich flowers attract butterflies, bees and other pollinating insects over a long season. Standing stems provide shelter for small invertebrates.

• Winter crown rot: improve drainage, keep the crown clear of wet mulch and avoid low spots that hold winter water.
• Powdery mildew: give plants full sun and space for airflow; water the soil rather than repeatedly wetting foliage.
• Slugs and snails on young shoots: protect emerging growth with barriers, hand-picking or locally approved iron-phosphate bait.
• Excessive self-seeding: remove flower heads before seeds mature and pull seedlings before they establish deep roots.

Not known to be toxic to cats, dogs, horses or people; no particular plant part is recognized as poisonous. It is not an edible plant, and substantial ingestion may still cause digestive upset.

Where it spreads. Self-seeds freely and can escape gardens. It is considered invasive in parts of California and Oregon and an environmental weed in parts of Australia, including New South Wales and Queensland. Check local guidance before planting; avoid it near susceptible natural areas and prevent seed production where escape is a concern.

• Slender vervain (Verbena rigida)

  Much shorter, usually 1-2 ft (0.3-0.6 m), with stiff, conspicuously toothed leaves and a spreading habit rather than tall, open branching.

• Blue vervain (Verbena hastata)

  Carries flowers along narrow upright spikes rather than flattened clusters, has more leafy stems and prefers moister soil.

The species name bonariensis means 'of Buenos Aires', while purpletop describes the purple flower clusters held at the tops of the stems.

Propagation. Grow from seed sown under cover in late winter or spring, or transplant young self-sown seedlings. Germination can be irregular, and a period of cold may help. Take softwood cuttings in spring or early summer to preserve a particular plant's characteristics.

Accepted botanical name

Verbena bonariensis

In the US and Canada

Introduced in Canada, Hawaii, the lower 48 states and Puerto Rico.

Native range

Argentina Northeast, Argentina Northwest, Argentina South, Bolivia, Brazil South, Brazil Southeast, Chile Central, Chile North, Chile South, Ecuador, Paraguay and Peru.

Measured

Average height 130 cm.

Sources: GBIF (CC BY 4.0), USDA PLANTS and Trefle (CC BY 4.0). The care and design notes are LandscapeGPT's own.