Jonathan, I’m just about retting wych elm bast fibres. The bast is still on the outer bark and has been drying for more than a year because I didn’t have the time.
I put the bark in a small stream which is very convenient because thus you always have fresh water around the bast and you get rid of the slime that is generated if you put the bast in a pond instead.
The bark that I’ve sunk is of different thickness. I’ve checked the less thick ones last Sunday after three weeks in the water. Although they separated ok, I would have prefered to let them in the water for another one or two week. On the thicker bark, the bast was still firmly attached and I suppose to leave them at least two months in the water. But I have read somewhere that up to three month for freshly collected bark/bast is ok too.
I don’t know anything about hickory bast fibers but if they are of the same quality as linden or elm bast fibers I would leave them in the water for at least two months and up to two months and check them every two weeks.
Elm bast after 3 weeks of retting
Elm bast collected from very fresh elm bark (pulled off the bark)