Perennial
Purpletop vervain
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Flowers | Flowers in July | Flowers in August | Flowers in September | Flowers in October | ||||||||
| Plant | Plant in April | Plant in May | Plant in June | |||||||||
| Prune | Prune in April | |||||||||||
| Looks good | Looks good in July | Looks good in August | Looks good in September | Looks good in October |
Overview
This South American plant sends up square, almost leafless stems that branch into flat heads of tiny lilac-purple flowers. Because it is so see-through, you can dot it near the front of a border and still look past it to the plants behind. Butterflies, bees and hoverflies visit it constantly. It behaves as a short-lived perennial in Britain and often survives only two or three winters, but seedlings keep it going.
Where to grow purpletop vervain
Full sun and free-draining soil are essential; it thrives in gravel gardens, between paving and on light sandy or chalky ground. Cold, wet clay is the usual cause of winter losses. The compact 'Lollipop' reaches around 60 cm and suits pots and small beds.
Planting
Plant after the last frost, spacing plants 40–50 cm apart in drifts rather than singly. Water them in, then only in prolonged drought once established.
Care through the year
Spring
Wait until new shoots show at the base before cutting old stems down.
Summer
No staking needed; the stems are tough. Water pot-grown plants regularly.
Autumn
Leave the stems standing for seed-eating birds and frost protection.
Winter
In cold, wet districts, a mulch of grit around the crown improves survival.
Pruning
Cut last year's stems back to just above fresh basal growth in mid-spring. Pinching young shoots in early summer gives bushier, slightly shorter plants.
Propagation
Self-sown seedlings are easy to lift and move in spring. You can also sow seed under cover in March; a spell in the fridge for a few weeks first speeds germination. Softwood cuttings root in summer.
Common problems
Powdery mildew can whiten the leaves in dry late summers but rarely harms flowering. Slugs may graze seedlings. Too many seedlings? Hoe off the extras while small.
Something else wrong? Diagnose it by symptom.
Month-by-month reminders
Jobs for this plant come round in April, May and June. Each month page lists everything else worth doing in the garden at the same time.
Related plants
Sources
Botanical names follow Kew's Plants of the World Online; growing attributes were checked against the references below. Text is our own. See our editorial policy.