Hi David,
I don't know what type of nettle you have. There are several sorts. I have had experience with tall nettle, starting about 47 years ago. I gew up in Ohio with a woods 50 ft behind my house (I now live in the Ozarks in North Central Arkansas). Nettle is one of the very best fibers you can make strings out of. I don't know what the weather has been like where you are. Here, we have had no frosts and it is ideal for harvesting nettle fibers. I used to make things out of nettle fiber simply by pulling the outer "bark" off the nettle. I did this while the plant was green. I learned how to spin when quite young (I am a blacksmith by trade now and learned that when young also), and I found if I twisted the fibers when green they were so strong they would cut through my hand when I would try and break this very fresh crude spun fiber of only one ply. You will know if it is a good time to collect fiber from nettle and milkweed by the fibers. You should be able to get fibers when you just pull off the bark. If the fibers are too short, the plant is immature. If they are long and week they are too old. Retting the fibers is not a bad way to get the fibers clean, but you can simply pull the bark off, dry it, and then work the fibers flear of the trashy part of the bark when it drys. By the way, retting and rotting come from the same root. retting is only partially rotting the stalk, done to make the trashy stalk and other part of the skin brittle before the fibers rot. If you do it too long the fibers will be weak.
The Traditional Bowyers Bible, I believe Volume 2, explains pretty well how to spin. My wife is a basket maker, spinner and weaver, and I ply what she spins on a spinning wheel on a Navajo type spindle, just plied some wool and silk together 2 days ago, so I still keep my hands in it.
Milk weed is pretty similar. The quality of the fibers varies from one time of year to another. And from one batch of plants. Nettle is generally a little stronger than milkweed, an both are at least as strong as linen. Linen varies according to the where the plant is grown and the climate. Hemp is supposed to be stronger than linen if grown correctly, but I have never dealt with it, and the imported fiber is generally not very good. Anyway, I would go out and strip some outer layers off the nettle, and twist them while green, and the fibers will show white amongst the green if it is still alive. If a frost has just hit it should be very good, but the skin will dry. I have worked with linen , breaking the stalks in a wooden device and then running them through a hetchel to comb out the trash after it was retted when I worked for a restoration in the late 1960's at Hale Farm and Village, Bath Ohio. But you can just strip the bark, let it dry, not ret it, and break the fibers out with no real problem, and I encourage you to experiment and do it a little. The spinning takes some time to learn. There are some books on it, but none will teach you how to work with nettle. If you get enough fiber and happen to be coming through the North Central Ozarks (I am an hour and a half South of Branson, MO in Arkansas) I could show you how to spin it. But there should be local spinners in your area. With the Internet you should be able to find some traditional spinners in your area and any of them should be able to help you learn the spinning part. Only a few might know the separating of fibers. But some will. I wish you great luck. The nettle fiber is as strong as you will find in North America, period. If you persist you can make some fine strings out of it. I always did this bare handed, though it stung some it never damaged me. You can eat green nettle tops, but the smell is pretty bad when you boil them!
