No, I never made a bowsting out of it.  At the time I had made one bow before I learned to work with nettle.  It was a lemonwood longbow, about 70 lbs pull when I was 12.  It broke after limited usage.  I built it along the line of a yew longbow, used information from The Archer's Craft by, I believe, Adrian Elliot Hodgkin (I'm going back in memory 47 years!!)  But while I could draw the bow It was too powerful for me at the time.  Anyhow, I have made a lot of cordage, but never a natural bowstring.  I haven't found any nettle locally, there is some milkweed.  I don't know how to identify dogbane.  Currently I'm recuperating from some surgery, spent a lot of time on the net, which is how I found this forum.  I have a nice hickory overbuilt flatbow, slightly recurved, with a (sorry for this) nylon cable back.  About 80 lbs, it seems to have very good cast.  I am wanting to make a few more bows soon, I have some really excellent hickory that was cut for me.  I have to get healed up and catch up on work (self employed, no insurance, I need to work!!) I am making my own shafts, and I have a nice, simple, 3 fletch jig I want to got pictures of and explanation on how to build on the 'net.  It will take me a while right now.