Sea lavender

Sea lavender: how do you recognise it?

Habit

Rosette of large leaves with flower sprays up to 60 cm tall; about 60 cm across in total.

Leaves

Large and leathery, 15–30 cm long, glossy dark green, in a rosette at ground level; partly evergreen in mild winters.

Flower

Dozens of small blue-violet flowers on fine, much-branched sprays, from July to September.

Colour

Lavender blue to blue-violet; the papery little calyces stay on for a long time.

Roots

A deep, fleshy taproot: the plant dislikes being moved and needs a permanent spot.

Flowering: July–September · Plants: March–May · Pruning: March

Why grow it?

• An airy cloud of lavender-blue flowers from July to September, above lovely, glossy foliage.
• Excellent as a cut flower and as a dried flower, lovely for years.
• Drought tolerant and resistant to wind and salt: a tough plant for sunny, poor soil.
• Bees and other insects visit the flowers.
• Long-lived and low maintenance, if it is in the right spot.

Sea lavender: where does it grow best?

• Full sun for the richest flowering; in shade it hardly flowers.
• Poor, well-drained soil: sand or loam, neutral to chalky. Avoid heavy clay.
• Dry to lightly moist; wet feet, especially in winter, will kill the plant.
• Choose a permanent spot straight away: it dislikes being moved. Allow 50–60 cm per plant.

Light

Sun

Soil type

Sand or loam

Acidity

Neutral or chalky

Moisture

Dry

Size

0.6 m tall, 0.6 m wide

Hardiness

Hardy (to -30 °C)

Goes well with

• Catmint: Blue flowers in the same sunny, well-drained soil.
• Sage: Blue-purple spikes that together form a cool cloud of colour.
• Globe thistle: Blue globes beside the airy cloud.
• Stonecrop: Drought tolerant and low, with pink flower heads in late summer.
• Ornamental grasses: Fine grass gives movement beside the rosette.

Sea lavender: when and how to plant it?

Plant in March–May.

1. Plant between March and May, when the soil is neither frozen nor waterlogged.
2. Dig a deep hole, because the taproot wants to grow straight down, and mix in sand or grit if the soil is heavy.
3. Set the plant at the same depth as in its pot, with the rosette at ground level, and disturb the root ball as little as possible.
4. Leave 50–60 cm between plants.
5. Water thoroughly after planting, then only in long dry spells during the first year.
6. Spread a layer of grit around the base; compost is not needed and holds too much moisture.

Care

Water

Water in dry spells during the first year. After that it almost always manages on its own thanks to its deep root.

Feeding

None or hardly any. On poor soil it looks best and stays compact.

Mulching

Use grit or pebbles, not compost or bark: they hold too much moisture around the rosette.

Spent flowers

You can leave the sprays: they are still attractive dried. Cut them off in late autumn or in spring.

Dividing

Better not: the taproot makes dividing difficult. Leave the plant in place; it gets bigger year after year.

Tip: It has a deep taproot: choose a permanent spot straight away in poor, well-drained soil. Hang the flower stems upside down to dry.

Sea lavender: when to prune it?

Pruning months: March.

When: In March, before the new leaves appear; flowers for a bouquet are cut in summer.

How:

• Cut the old, dead flower sprays back to the rosette.
• Remove dead, brown leaves at the base by hand or with scissors.
• Cut the flowers for a bouquet or for drying in July–August, when most of the little flowers are open.
• Hang the stems upside down in a dry, dark, airy place to dry them.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Seed

In spring on sandy seed compost, lightly covered, in a warm spot. Germination is slow; seedlings flower after two to three years.

Root cuttings

In winter (December–February): pieces of thick root 5–8 cm long in sandy compost, upright, with the top end just at the surface. For experienced gardeners.

Sea lavender: how does it get through the winter?

Hardy to −30 °C.

• Fully hardy, to about −30 °C: no protection is needed in Belgian winters.
• The danger is winter wet: choose free-draining soil and avoid low, damp spots.
• In a pot (less suitable because of the deep root): use a deep pot with gritty compost and stand it in a sheltered spot.

Diseases and pests

• Root rot: Plants wilt or die in wet, heavy soil. Plant in free-draining soil and mix grit into the ground.
• Slugs: Young leaves get nibbled in spring. Collect slugs in the evening.
• Mildew or leaf spots: White powder or spots on the leaves in damp, stuffy weather. Leave space, avoid overhead watering and cut off affected leaves.
• No flowers: Too much shade, too little sun or soil that is too rich. Do not move it, but choose a sunny, poor spot for new plants.

Through the year

• March: Cut off old sprays and dead foliage. Plant.
• April: Plant. Watch for slugs.
• May: Plant. Leaf growth.
• June: Flower stems develop.
• July: Flowering begins. Cut for a bouquet or for drying.
• August: Full flower. Cut for dried bouquets.
• September: Flowering. Bees visit the flowers.
• November: Leave the sprays or cut them off. Keep dry.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Did you know?

• Sea lavender is not related to true lavender; the plant belongs to the plumbago family, Plumbaginaceae.
• The species name platyphyllum means ‘broad-leaved’, after the large leaves.
• The small calyces of the flowers stay on after the petals fade, which is why the dried stems stay attractive for years.