Blue vervain

Blue vervain: how do you recognise it?

Habit

Perennial 1–1.5 m tall and 40–50 cm wide, with upright, square, branched stems.

Leaves

Opposite, lance-shaped to narrowly oval, 8–15 cm, toothed and rough at the edge; sometimes with a few lobes at the base.

Flowers

Small flowers in slim spikes 10–15 cm long, grouped in a candelabra-shaped panicle, from July to September.

Colour

Blue-purple; white and pink cultivars also exist.

Roots

A fibrous root system that stays shallow in moist soil and divides easily.

Flowering: July–September · Sowing: March · Plants: April–May and September · Pruning: March

Why grow it?

• Flowers from July to September with blue-purple candelabras, when many other perennials are nearly over.
• Attracts bees, bumblebees and butterflies.
• The upright, open habit adds structure without taking up much space.
• Suits moist soil and even the edge of a pond.
• Self-seeds, giving you free new plants.

Blue vervain: where does it grow best?

• Full sun: the more sun, the sturdier the stems and the richer the flowering.
• Moist to wet soil: loam, clay or peat; acid to chalky.
• Normal to moist soil also suits, as long as it does not stay dry for long.
• Allow 50 cm per plant; in groups of three to five plants it looks its best.

Light

Sun

Soil type

Loam, clay or peat

Acidity

Not fussy

Moisture

Normal or wet

Size

1.2 m tall, 0.5 m wide

Hardiness

Hardy (to -30 °C)

Goes well with

• Purple coneflower: Pink flowers with a brown cone, in flower at the same time.
• Helenium: Warm yellow and orange tones next to the purple candelabras.
• Garden phlox: Pink and white panicles in the same sun and moist soil.
• Ornamental grasses: Light stems give a natural, prairie-style feel.

Blue vervain: when and how to plant it?

Plant in April–May and September.

1. Plant in April–May or in September, when the soil is neither frozen nor waterlogged.
2. Dig a hole twice as wide as the root ball and mix in compost.
3. Set the plant at the same depth as in its pot and firm the soil well.
4. Space plants 50 cm apart.
5. Water in generously straight away and spread a layer of leaf-compost mulch around the base.

Care

Water

Keep the soil moist; in dry summers water generously every week, otherwise the foliage droops.

Feeding

A spade of compost or organic fertiliser in spring is enough.

Mulching

A layer of leaf compost in spring keeps the soil moist and cool.

Support

In a windy spot a plant support can keep the tall stems upright.

Dividing

Divide the clump every 3–4 years to keep it vigorous; it remains short-lived anyway.

Tip: Leave the stems standing in winter and cut them only in March: the seeds fall and new plants appear. This is how you keep this short-lived vervain in the garden.

Blue vervain: when to prune it?

Pruning months: March.

When: In March, before the new shoots start to grow.

How:

• Cut last year’s dried stems down to just above the ground.
• Leave the seed heads standing over winter: they decorate the garden and feed birds.
• For more compact plants, shorten the shoots by a third in May; flowering then comes slightly later.

Caution: It seeds itself readily: cut off the spikes before the seed ripens if you do not want seedlings.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Seed

In March indoors: the seed needs cold, so first keep it for 4–6 weeks in moist sand in the fridge. Then sow at 18–20 °C, prick out and plant out after the last frosts.

Division

In spring cut the clump with a spade into pieces with roots and buds, and replant straight away.

Cuttings

In May–June take tip cuttings of 8–10 cm in moist cutting compost; they root within a few weeks.

Blue vervain: how does it get through the winter?

Hardy to −30 °C.

• Fully hardy, to about −30 °C: no protection is needed in Flanders.
• Leave the faded stems standing over winter; they protect the crown and shelter insects.
• It is short-lived: let it self-seed or divide it every 3–4 years, so that there are always young plants.
• In a pot: put it in a sheltered place and never let the pot dry out.

Diseases and pests

• Powdery mildew: White powder on the leaves in a hot, dry summer. Water, leave space and cut off affected leaves.
• Drooping foliage: A sign of drought: water generously and mulch the soil.
• Slugs: Nibbled young shoots in spring. Collect them in the evening and scatter coarse bark around the clump.
• Aphids: On young shoots and buds. Rinse them off with water; ladybirds help.

Through the year

• March: Cut back to just above the ground. Add compost. Sow indoors.
• April: Plant. Divide. Apply mulch.
• May: Plant. Fit supports. Take cuttings. Shorten shoots if you like.
• June: Water in dry weather. Take cuttings.
• July: Flowering begins.
• August: Full flower. Water in dry weather.
• September: Flowering. Plant or divide.
• October: Leave the seed heads.
• November: Rest.
• December: Rest.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Butterflies

Nectar for butterflies.

Did you know?

• The stems are square, a feature shared by many plants in the vervain family.
• The species name hastata means ‘spear-shaped’ and refers to the lobes at the base of the leaf.
• The small flowers open in a ring from the bottom upwards, so a single spike can stay in flower for weeks.