Why the Right Moment Matters

Flax gives you two harvests in one plant, and they do not ripen at the same time. The fibre in the stem is at its finest when the seed is barely formed; the seed itself is only worth collecting once the capsules have dried and the kernels have hardened. If you are growing a dual-purpose crop, you will have to choose which one you want most, because the two windows sit roughly three weeks apart. Most home growers in the UK pull their flax somewhere between late July and mid-August, but the calendar is far less reliable than the plant itself. Counting days from sowing helps — fibre flax is usually ready around 90 to 100 days, seed crops nearer 110 to 130 — but always let the field have the final word.

Reading the Signs: Leaves, Stems and Bolls

The first clear signal is the lower third of the stem. Those bottom leaves begin to yellow and drop, and the stalk beneath them loses its green and takes on a soft straw colour. Work your way up the plant: the middle should be yellowing, while the topmost leaves and the stem around the seed capsules still hold a little green. The capsules — the small round bolls that follow the blue flowers — shift from green to a pale gold, and the whole patch takes on that unmistakable ripening haze. Run a hand up a bundle of stems: at the right moment they feel firm and slightly dry, not limp and sappy. If the stems have gone grey-brown and brittle right to the tip, you have waited too long for fibre.

The Rattle and Squeeze Tests

When you think you are close, use your hands and your ears.

• The rattle test: shake a few seed capsules next to your ear. Silence means the seed is still soft and wet; a dry, papery rattle means the kernels have shrunk away from the husk and are ready.
• The squeeze test: split a capsule and press a seed between your thumbnails. Immature seed is pale, milky and squashes easily. Ripe seed is flat, glossy and dark or golden-brown depending on variety, and the kernel inside is firm and pale.
• The stem snap: bend a stem a few inches above the ground. Fibre-ready flax bends and creases; over-ripe flax snaps cleanly, a sign the fibre has lignified and will spin up harsh.

Harvesting for Fibre

For handspun linen, aim for what growers call the early yellow-ripe stage: lower leaves shed, the lower half of the stem yellowed, capsules just turning from green to gold, and still a touch of green in the upper leaves. This is when the bast fibres peel away in long, silky ribbons. Pull the plants rather than cutting them — the roots add several inches of the longest fibre, and pulling is traditional for good reason. Choose a dry morning once the dew has lifted, pull in small handfuls, and tie them into bundles about the thickness of your wrist.

Stand the bundles in loose shocks, capsules upward, somewhere airy and out of the rain, and leave them to dry before retting. If rain is forecast for days on end, bring them under cover; wet flax in a heap will rot rather than ret.

Harvesting for Seed

If your priority is seed — for sowing next year, for baking, or for oil — patience pays. Wait until every capsule has turned a dry golden-brown and the stems are largely brown, then test a few bolls daily. The whole crop can be cut, bundled and stood in shocks to finish ripening, with a sheet or tray underneath to catch any seed that falls. Once the bundles are bone dry, thresh by rubbing the capsules between your hands or beating the bundles against the inside of a clean bin. Winnow the chaff away on a breezy day or with a gentle fan.

Store the seed in paper bags or glass jars somewhere cool and dark, and it will keep its viability for several years. You can still ret the stems afterwards, though the fibre will be coarser than an early-pulled crop.

Weather, Timing and the Final Check

UK summers are rarely tidy, so walk the crop every couple of days from mid-July onwards. Wind and heavy rain can flatten flax overnight, and lodged stems are far harder to pull and much more prone to mould. A hot, dry spell will push ripening forward by a week or more; a cool, wet one will hold it back. If a storm is coming and the crop is nearly there, it is usually better to pull a little early than to watch it go down.

And if you are ever unsure, pull a single bundle, dry it, and try retting and spinning a small sample. A few stems will tell you more than any rule of thumb.