Flax and relatives - The Manual of Seed Saving - page 123

tolerate late frosts as low as 23°F (−5°C). When flax is sown in 8 in. (20 cm) rows, it is easier to weed.
Weeding is especially important early, until plants are 4-5 in. (10-12 cm), at which point they begin to
be able to suppress weeds on their own.
Flax seeds
HARVEST Seeds ripen in mid to late summer. Capsules of convar. usitatissimum remain closed; those
of convar. crepitans open upon ripening and therefore must be harvested before fully ripe (crepitans
flax is rarely grown today). Cut entire plants when they turn brown and seeds rattle inside the capsules.
Plants must then completely dry, indoors if necessary. For larger quantities, draw plants across a bed of
nails to remove capsules from stalks. Thresh in a cloth bag, winnow with the wind and sieves.
Green-ripe and dead-ripe flax seed capsules