I have been putting this task off because these stems looked so little promising.
The stems mostly shattered without fibre becoming evident in any significant way.
I gathered just a little fibre for a lot of effort.
After carding, I was left with this. So I cleaned my handcards on the garden, added the stems to the mulch in the garden, and now… I wait for next year!
A belated postscript: there is a wonderful community flax growing project reaching the spinning stage on the other side of the planet. So for stories of bast fibre success, please go to visit Sharon Kallis here.