Perennial flax

Perennial flax: how do you recognise it?

Habit

Loose, airy clump 40–50 cm tall and about 30 cm wide, with many thin, arching stems.

Leaves

Narrow and lance-shaped, about 2 cm long, grey-green and scattered along the stems.

Flower

Saucer-shaped, about 2.5 cm across, sky blue with fine veins; from May to August. Each flower lasts one day.

Fruit

Small, round seed capsules with glossy brown seeds after flowering.

Roots

Deep taproot: it tolerates drought well but resents being moved when older.

Flowering: May–August · Sowing: March–May · Plants: April–May · Pruning: March

Why grow it?

• Sky-blue flowers for four months, a colour that is rare in the summer border.
• A light, see-through plant that lets other perennials show through without shading them.
• Very drought tolerant and undemanding: it suits a gravel garden or a dry, sunny border.
• The flowers attract bees.
• In a suitable spot it seeds itself, so you keep getting new plants.

Perennial flax: where does it grow best?

• Full sun: in part shade it flops and flowers less.
• Poor to moderately fertile, well-drained sandy or loamy soil, preferably neutral to chalky.
• Dry to normal moisture: wet, heavy clay in winter is fatal to the roots.
• Suits a rock garden, gravel garden, dry slope and sunny edge.
• Allow 25–30 cm between plants; preferably plant a few together.

Light

Sun

Soil type

Sand or loam

Acidity

Neutral or chalky

Moisture

Dry

Size

0.5 m tall, 0.3 m wide

Hardiness

Hardy (to -30 °C)

Goes well with

• Ox-eye daisy: White flowers that contrast softly with the sky blue.
• Evening primrose: Yellow in the evening, same sun and the same dry soil.
• Ornamental grasses: Light plumes that support the airy plant.
• Catmint: Blue spikes that enjoy the same dry, sunny position.
• Stonecrop: A low plant that covers the base without holding too much moisture.

Perennial flax: when and how to plant it?

Plant in April–May.

1. Plant in April or May, once the soil has warmed up.
2. Dig a hole as deep as the pot and twice as wide; open up heavy soil with coarse sand or grit.
3. Set the plant at the same depth as in its pot and firm the soil lightly around it.
4. Space plants 25–30 cm apart in groups of three to five for an airy effect.
5. Water well straight away, then only during long dry spells.
6. Leave the soil bare or spread grit; no thick layer of compost or bark around the crown.

Care

Watering

In the first year during long dry spells; after that no longer needed.

Feeding

Not needed. Rich soil gives long, floppy stems and shortens the plant’s life.

Spent flowers

Cut off faded stems to prolong flowering. Leave a few in August if you want it to self-seed.

Mulching

Only with grit or gravel, to keep the crown dry.

Renewing

The plant is short-lived. Let it self-seed or sow again every few years so you always have young plants.

Tip: Each flower lasts only a day, but new ones keep coming for weeks. Give it poor, dry soil and let it self-seed, because the plant is short-lived.

Perennial flax: when to prune it?

Pruning months: March.

When: In March, before the new shoots start. In summer you also cut off faded stems.

How:

• In March, cut the old stems back to a few centimetres above the ground.
• Between May and August, cut faded stems back to just above a side shoot.
• Late in the season, leave a few stems for seed if you want natural self-seeding.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Sowing indoors

In March, in a tray of sandy seed compost, on the surface and barely covered. Keep lightly moist; seeds germinate in two to four weeks. Plant out after the last frosts.

Sowing outdoors

In April–May, straight into a sunny, well-drained spot. Thin later to 25–30 cm.

Self-seeding

The plant seeds itself; move the seedlings while still small, as they have a deep taproot.

Perennial flax: how does it get through the winter?

Hardy to −30 °C.

• Fully hardy, down to about −30 °C: no protection is needed in Belgian winters.
• The danger is not frost but lasting wetness: make sure the soil drains well.
• In a pot: stand it against a wall, under a roof or somewhere the pot does not become waterlogged.

Diseases and pests

• Root rot: Limp, yellow-brown plants in wet, heavy soil. Improve drainage with grit or choose another spot.
• Floppy growth: In shade or rich soil the stems fall over. Give more sun and no feed.
• Slugs: Young plants and seedlings get nibbled. Collect the slugs in the evening.
• Aphids: Sometimes on young shoots. A jet of water is usually enough.

Through the year

• March: Cut old stems back. Sow indoors.
• April: Plant. Sow outdoors.
• May: Plant or sow. Flowering begins.
• June: Flowering. Cut off faded stems.
• July: Flowering. Cut off faded stems.
• August: Last flowers. Leave a few stems for seed.
• September: Move seedlings if needed.
• November: Check that rainwater drains away well.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Did you know?

• The flowers open in the morning and usually drop their petals during the day, so the plant looks ‘new’ every day.
• The genus Linum is best known for common flax, whose fibres give linen and whose seed gives linseed.
• In the wild, perennial flax grows on dry grassland and mountain pastures across large parts of Europe.