Linum perenne aka Blue Flax

Linum perenne is known as blue flax or perennial flax. It belongs to the flax family, Linaceae. Its native range spans east-central Europe, Siberia, and China. It has also spread into western and central North America. This short-lived perennial forms small tufts of slender stems. Garden plants reach 1–2 feet [0.30–0.61 metres] tall. Their spread is about 0.75–1.5 feet [0.23–0.46 metres]. RHS gives a slightly wider upper spread of 1.64 feet [0.5 metres].

The thin stems look fragile, but their fibres resist breaking. Stems rise from the base and stand upright or sprawl. The narrow leaves look grey-green or blue-green. They have smooth edges and no hairs. Dense groups of leaves give the stems a whorled look. Some leaves remain through winter, making the plant semi-evergreen. Its light, open form suits the front of garden borders.

Blue flowers appear in late spring and early summer. May and June form the main bloom period. Each flower has five petals marked with darker blue veins. Flowers measure about an inch across. Buds nod in clusters at the tips of stems. The flowers turn upright as they open. Each bloom opens in morning sun and lasts one day. Petals often fall before evening, but new blooms replace them. Flowering can last eight weeks, or twelve in favourable conditions. Round brown capsules follow, holding ten flat seeds.

Give this flax full sun and soil that drains well. It accepts some shade but flowers best in sun. It tolerates heat, drought, and dry or rocky ground. Clay can lead to shallow roots and poor winter survival. Sources place it in USDA zones 5–8, with Chicago listing 4–8. RHS rates its UK hardiness H4. Grow it in rock gardens, meadows, or informal borders. Groups of plants give a stronger flower display. Seeds and stem-tip cuttings provide new plants. It can self-seed freely where conditions suit it. Cutting some stems back halfway through flowering can extend bloom.

Serious pest and disease problems are uncommon. Cutworms, grasshoppers, aphids, slugs, and snails may cause damage. Stem fibres have served for cloth, rope, and paper. Seed oil also has recorded uses in lighting and coatings. PFAF records traditional medicinal uses, without establishing their effectiveness. It lists cooked seeds as food, with a nutty taste. Raw seeds contain cyanide and must not be eaten raw.