There's a New World flax that makes a pretty cottage garden flower, with pale blue flowers on long tough stems. Tying bundles of these stems to the downspout in winter does not turn them into recognizable flax, alas. But then I didn't know what I was looking for -- this little leaflet has line-drawings of how the stems should be coming apart when the fiber is ready to be freed.
It's a microbial process, of course, eating away everything but the final desirable fiber; no wonder linen is so long-lasting when we get it free.
There are lots of tactics, or were, when it was more done, depending on whether the area was warm or cool, well-watered or frosty or only dewy when the crop came in. Some made it whitest, some strongest. Some required a lot of labor and some more labor than that.
The leaflet was reprinted by the Caber Press, which specializes in reissuing reference works for `material culture', q.v.; there's an 1895 report on hemp culture, if you want to start at the beginning.
You could also get the original Industrial Fermentations, The Chemical Catalog Company, 1926; or U.S.D.A. bulletins 1185 and 669. Maybe.
So wrote clew in Clothing. , Technology.