Blue eryngo

Blue eryngo: how do you recognise it?

Habit

Upright, branching perennial 60–90 cm tall and 45–60 cm wide, growing from a leaf rosette.

Leaves

Rosette leaves oval to heart-shaped, leathery, scalloped and not spiny; the stem leaves are smaller, cut and spiny.

Flowers

Countless rounded heads 1–2 cm across, each with a ruff of narrow, spiny bracts, from July to September.

Colour

Steel blue to amethyst blue; the upper stems turn blue too.

Roots

A long, deep taproot: it dislikes being moved.

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

Why grow it?

• A magnet for bees and butterflies: in July and August the flower heads swarm with insects.
• Striking blue and strong structure in the border, from July to September.
• Needs no watering once established: ideal for a gravel garden or dry border.
• A lovely cut flower that dries easily and keeps its colour.
• The faded stems stay decorative into winter, especially when touched by frost.

Blue eryngo: where does it grow best?

• Full sun: only then does it colour well and stay sturdy.
• Poor, free-draining sandy or loamy soil, acid to chalky.
• Dry to moist; wet soil in winter makes it rot.
• On rich soil it grows soft and flops: no compost or fertiliser.
• Allow 40–50 cm between plants.

Light

Sun

Soil type

Sand or loam

Acidity

Not fussy

Moisture

Dry or normal

Size

0.8 m tall, 0.5 m wide

Hardiness

Hardy (to -35 °C)

Goes well with

• Globe thistle: Blue globes too, but larger; together a feast for bees.
• Yarrow: Flat heads in yellow or terracotta beside the small blue globes.
• Russian sage: A silver-grey, violet-blue haze in the same dry, sunny soil.
• Feather grass: A fine, airy grass that softens the bold thistle shape.
• Catmint: A low, long-flowering blue foreground.

Blue eryngo: when and how to plant it?

Plant in March–May.

1. Plant from March to May, preferably young pot-grown plants.
2. Choose its permanent spot straight away: because of the taproot it is hard to move later.
3. Dig a deep hole and, in heavier soil, mix in some coarse sand or gravel.
4. Set the plant at the same depth as in the pot and space plants 40–50 cm apart.
5. Water when planting and in dry spells for the first few weeks; after that it is no longer needed.

Care

Water

Only while it establishes. After that it manages alone, even in dry summers.

Feeding

Avoid: fertiliser makes the stems soft.

Support

Not needed on poor soil in sun. On richer soil a plant support or a sturdy neighbour helps.

Drying

Cut stems when the heads are fully blue and hang them upside down in a dry, dark, airy place.

Gloves

The bracts and stem leaves are prickly: wear gloves when cutting.

Tip: Only cut stems for drying once the heads are fully blue, and hang them upside down in a dry, dark place: that keeps the colour best.

Blue eryngo: when to prune it?

Pruning months: March.

When: In March, after leaving the faded stems standing through winter. Flowers for drying are cut in July–August.

How:

• Leave the faded stems in autumn: covered in frost they are a winter feature.
• In March, cut them back to just above the new leaves at the base.
• If you want fewer seedlings, remove the heads after flowering, before the seed ripens.

Caution: Wear sturdy gloves: the bracts and the leaves on the stems are prickly.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Root cuttings

In December–February, take 5 cm pieces of taproot and push them upright into a pot of sandy compost, the top just below the surface. They sprout in spring.

Self-sown seedlings

It sometimes self-seeds. Move seedlings while very young, before the taproot goes deep.

Blue eryngo: how does it get through the winter?

Hardy to −35 °C.

• Very hardy, to about −35 °C: in Belgium it needs no protection.
• Wet soil is the only real danger: make sure drainage is good.
• The faded stems give the border structure; don’t cut them until March.
• In a pot: choose a deep pot with a drainage hole and keep it out of the worst rain.

Diseases and pests

• Floppy stems: Soil too rich or too little sun. Don’t feed and choose a sunnier spot.
• Root rot: In wet, heavy soil, especially in winter. Replant in a drier spot or on a raised mound with gravel.
• Powdery mildew: White powder on the leaves in dry late summers; usually harmless. Space plants well and remove affected leaves.
• Slugs: Eat the young rosette leaves in spring. Pick them off in the evening.

Through the year

• January: Take root cuttings.
• March: Cut back old stems. Plant.
• April: Plant. Protect young rosettes from slugs.
• May: Plant until the end of May. Stems are growing.
• July: Flowering begins. Cut for drying when the heads are blue.
• August: Full flower, with bees and butterflies. Dry flowers.
• September: Last flowers. Remove heads if you want to limit self-seeding.
• October: Leave the faded stems standing.
• December: Take root cuttings.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Butterflies

Nectar for butterflies.

Did you know?

• Despite its thistle-like looks, it belongs to the carrot family, along with carrot, fennel and parsley.
• A related species, sea holly, grows in the Belgian dunes, where it is rare and protected.
• Planum means ‘flat’ and refers to the flat, undivided rosette leaves.