Alpine sea holly

Alpine sea holly: how do you recognise it?

Habit

Upright clump 60–70 cm tall and about 45 cm wide.

Leaves

Basal leaves heart-shaped, long-stalked and toothed; the stem leaves are smaller and more deeply cut.

Flower

Cone-shaped flower heads 3–4 cm long, surrounded by a ruff of fine, feathery bracts.

Colour

Steel blue to violet blue, as are the upper stems and leaves.

Roots

Long taproot: it goes deep and dislikes being moved.

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

Why grow it?

• Spectacular, metallic-blue flower heads with a soft, lacy ruff.
• A magnet for bees, bumblebees and butterflies in July–August.
• An excellent cut flower, fresh or dried: the blue colour lasts a long time.
• Drought-tolerant once established, and little work.
• The spent heads stay attractive into winter.

Alpine sea holly: where does it grow best?

• Full sun: that is where it colours the deepest blue.
• Free-draining sandy or loamy soil, acid to chalky; it accepts slightly richer soil than most sea hollies.
• Dry to moist in summer, but never wet in winter.
• A spot with some shelter from strong wind keeps the stems upright.
• Plant 40–45 cm apart, in groups of 3 or more.

Light

Sun

Soil type

Sand or loam

Acidity

Not fussy

Moisture

Dry or normal

Size

0.7 m tall, 0.45 m wide

Hardiness

Hardy (to -30 °C)

Goes well with

• Yarrow: Flat heads in yellow or pink beside the blue ones.
• Catmint: A soft blue companion at the base.
• Feather grass: Airy stems that soften its bold shape.
• Roses: A classic combination in a sunny border.
• Golden marguerite: Golden daisies as a warm contrast with the steel blue.

Alpine sea holly: when and how to plant it?

Plant in March–May.

1. Plant from March to May, ideally a young plant from a pot: the taproot dislikes disturbance.
2. Dig a deep hole so the taproot can go straight down; in heavy soil, mix in gravel.
3. Set the plant at the same depth as in the pot without damaging the root ball.
4. Leave 40–45 cm between plants.
5. Water well and keep the soil slightly moist for the first weeks.
6. Choose its permanent spot straight away: moving it later rarely succeeds.

Care

Watering

In dry spells during the first year; after that only in long dry periods.

Feeding

A thin layer of compost in spring is enough.

Support

In an open, windy spot or rich soil the stems may flop; a low plant support helps.

Cutting and drying

Cut the flowers when they are fully blue and hang them upside down in a dry, airy place.

Spent flowers

Leave them: they look lovely in autumn and winter.

Tip: Buy a young plant in a pot and put it straight into its permanent spot: the taproot dislikes being moved. Cut the flowers for drying when they are fully blue.

Alpine sea holly: when to prune it?

Pruning months: March.

When: Leave the spent stems standing all winter and cut them down in March, before the new leaves emerge.

How:

• In March, cut the dead stems down to just above the new rosette of leaves.
• For the vase or for drying, cut flowers with a long stem in July–August.
• Wear sturdy gloves: the stem leaves have spiny edges.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Root cuttings

In January–February, while the plant is dormant: cut pieces of about 5 cm from thick roots, insert them upright in a pot of sandy compost, top end up, and keep them cool and slightly moist.

Seed

The seed needs a cold spell: sow it in autumn in a pot placed outdoors. Germination can be slow and erratic.

Alpine sea holly: how does it get through the winter?

Hardy to −30 °C.

• Hardy to about −30 °C: no protection is needed in Belgium.
• Wet soil in winter is a risk, though: the taproot can rot. Ensure good drainage.
• Leave the spent stems standing: covered in frost, they are a winter ornament.

Diseases and pests

• Root rot: The plant fails to reappear after a wet winter. Plant in free-draining soil or on a slightly raised spot.
• Slugs: Young leaves are eaten in spring. Check in the evening and pick off the slugs.
• Powdery mildew: White powder on the leaves in dry summers. An airy spot and water during long droughts help.
• Flopping stems: In soil that is too rich or in shade the stems become floppy. Plant in more sun and feed less.

Through the year

• January: Take root cuttings from older plants.
• March: Cut away dead stems. Plant.
• April: Plant. Apply compost. Watch out for slugs.
• May: Last chance to plant. Add support if needed.
• June: Stems and flower buds start to turn blue.
• July: Flowering. Cut flowers for the vase or for drying.
• August: Full flower. Bees and butterflies visit.
• September: Leave the spent heads standing.
• December: The dry heads decorate the winter garden.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Butterflies

Nectar for butterflies.

Did you know?

• The blue ruff is not made of petals but of bracts; the true tiny flowers are packed together in the cone-shaped head.
• Although it looks like a thistle, it belongs to the carrot family, like carrot and parsley.
• In the wild it has become rare and is protected in several Alpine countries.