Flax (Linum usitatissimum) is an annual summer flower with sky-blue flowers on slender stems that grow 70-99 cm tall. It is the same plant that gives us linseed, linseed oil and linen. Flax is sown directly where it is to grow in April or May, thickly and in full sun, and flowers in July and August. The seed capsules are ripe about 110 days after sowing.
How to sow flax
Flax is sown where the plants are to stand. The seeds are 4-7 mm long and easy to place one at a time.
Choose a site: full sun and a deep, humus-rich soil. Flax does not tolerate ground where water lies, and heavy clay or dry sandy soil suits it poorly.
Sow when the soil is warm: in April or May, once the soil has warmed up after winter.
Prepare the bed: rake the soil to a fine tilth and water it thoroughly before you sow. That is how we get the most even germination.
Sow in rows: draw rows 10 cm apart, place one seed every 5 cm and cover with 0.5 cm of soil.
Keep the surface moist: the seeds germinate in 10-20 days. Water with a fine spray so the seeds are not washed out.
We describe how row sowing and broadcast sowing work in the article on direct sowing, and you will find more varieties that are sown the same way among our seeds for direct sowing.
Dense for fibre, sparse for seed
Flax is sown thickly. We recommend 5 cm between plants and 10 cm between rows, which comes to about 200 plants per square metre. A packet of common flax seeds contains 125 seeds and is enough for just over half a square metre.
The density decides what you get. A dense stand gives more fibre, a sparser one gives more seed. That leads to a simple rule for sowing. For flowers, dried capsules and linseed, sow at the spacing above and let the plants ripen fully. For your own fibre trial, sow a separate row closer than 5 cm and pull it 7-10 days before the seeds are ripe. One and the same row will not give you both the best fibre and ripe seed.
From sowing to harvest
The times in the table assume sowing in early May. If you sow earlier or later, the months shift by about the same amount.
| Stage | Time after sowing | When sown in early May | What to do |
|---|---|---|---|
| Sowing | 0 days | Early May | Sow 0.5 cm deep with 5 cm between seeds and 10 cm between rows |
| Germination | 10-20 days | Second half of May | Keep the soil surface moist |
| Growth | 3-10 weeks | May and June | Water in dry spells and do not feed |
| Flowering | About 10 weeks | July | Look in the morning. The stand flowers for about 2 weeks |
| Green seed capsules | About 12 weeks | Late July | Cut stems for bouquets and drying |
| Ready to pull for fibre | About 100 days | Mid-August | Pull up with the roots once the stems have turned yellow |
| Ripe seed | About 110 days | Late August | Harvest when the capsules are yellow and starting to split |
Flowers that open in the morning
Each flower is 15-25 mm across and has five petals. It opens early in the day and drops its petals the same day, so a bed of flax is blue in the morning and green again by the afternoon. Pollination takes place inside the closed bud, before the flower opens. New buds open day after day, and a stand flowers for about two weeks.
That decides how you use flax in a vase. A single flower does not last the day, so cut flax for the sake of its stems and buds. The straight stems with small green capsules add air between larger flowers in a bouquet. You will find larger flowers to combine the flax with among our seeds that are good for cutting, and we describe how to plan a bed of annual cut flowers in the article on growing cut flowers.
Seed capsules for drying and linseed for baking
The capsules are round and 5-9 mm in size. Each one has five compartments with two seeds in each, so up to 10 seeds per capsule. When we dry flax, it is the capsules we use. Cut the stems when the capsules are fully grown, bunch 5-10 stems together and hang them upside down somewhere dark and dry. How to dry more varieties and how long they need to hang is covered in the article on drying flowers.
If you want linseed, leave the capsules on the plant until they are yellow and have just begun to split, about 110 days after sowing. Cut the stems, let them finish drying indoors for a few days and rub the capsules between your hands over a bowl. The seeds are glossy and brown and consist of about 40 per cent fat, the oil that is pressed into linseed oil. Only use ripe seeds. Raw, unripe linseed contains cyanogenic compounds, which break down when heated, for example when the seeds are baked into bread. Save a handful for next spring. Flax pollinates itself, so home-saved seed usually comes true to the parent plant.
How flax was pulled and retted
Flax has been grown in Scandinavia since the Iron Age, from around 500 BC, and in the late 19th century Belfast was the world's largest centre of linen manufacture. The species name usitatissimum means "most useful". Fibre flax was not cut. It was pulled up by the roots to get the longest possible fibres. The sheaves were then retted, either spread out on the ground for 2-5 weeks, known as dew retting, or sunk in a pond or stream for anything from a few days to a few weeks. Scandinavia was once known for water-retted flax. During retting, microorganisms break down the pectin that holds the fibres to the woody part of the stem. After drying, the stems were broken, scutched free of woody remains and hackled through combs until only the long fibres were left, ready to be spun.
Common flax and perennial flax
Perennial flax (Linum perenne) is a separate species. It grows up to 90 cm tall and has blue flowers 2.5-5 cm across, larger than the 15-25 mm flowers of common flax. The species grows wild in Europe, mainly in the Alps. Common flax is annual, dies after setting seed and has to be sown again every spring, but it is the species grown for fibre and linseed. Choose perennial flax if you want flax that comes back in the border year after year. Choose common flax for cutting, seed capsules, linseed or your own fibre trial.
Common mistakes
Sowing too deep: 0.5 cm of soil over the seeds is enough. Do not rake them in any deeper.
A fed bed: too much nitrogen makes the flax fall over and gives poorer fibre. Flax manages on little fertiliser, so choose a bed that has not been fed this year.
Drought in May and June: flax needs around 120 mm of water during the two months when it grows most. If it does not rain, water about 14 litres per square metre a week.
Cut fibre flax: if you cut the stem, you lose fibre length. Pull up the whole plant with its roots once the stems have turned yellow.
Seed and fibre from the same row: fibre flax is pulled 7-10 days before it is fully ripe, and the seeds are not ready then. Label the rows when you sow.
Expecting blue in the vase until evening: the petals fall on the same day the flower opens. Plan the bouquet around stems and capsules, not around the blue flowers.
Author: Emma Vogiatzi
Fact-checked by Erik Hoekstra
Last updated 2026-11-04