So last Saturday I made a piece of cordage from stinging nettle then I tore the end so I stopped because I didn't have much more fibers anyway. Because I made it fresh it was full of water which soaked my skin and I got blisters during work. I think the technique is called reverse-wrap and it needs for me to hold the cord tight and twist it which was hard on my wet skin.
Next day I gathered more nettle and processed it into fibers (look at those hairs on pic #2) and let it dry for a day which also gave some time for my hands to heal. Then I started a new cord and made a little bit every day. Now I have 2m and 30cm long cordage and enough fibers for at least the double of it if not triple.
I primitive technology nao!