Leave the nettles in the ground till the spring, February/ May depending on the weather.
Pick the old stems, which are still standing, just as the new nettles are coming up. The old nettles will not sting you then, but the new shoots will, so you may still need gloves.
Store the stems in a warm, well ventilated place, ideally with some sunlight, like a greenhouse. Keep the stems until completely dry, best of all leave them for a year or two!
Fold the stems gently three or four times until you have a bundle small enough to fit into your oven. Wrap in a thin cotton cloth and bake in an oven at about 70°C, for an hour, or longer at less, until they become brittle. The bottom oven of an Aga or Rayburn works.
Lay the stems, still wrapped in cloth, on a hard, uneven surface and beat them with the edge of a flat stick, similar to a cricket bat. Shake and wring your wrapped bundle every now and then, rearranging within the cloth so that the stems are lying parallel. You can also try putting the wrapped bundle through a mangle or place it on the floor and dance on it!
Unwrap the cloth, and you will see that the fibres are lying together on top and the hard woody bits have fallen off. Pick out the fibres by hand.
With a pair of hand carders or a drum carder and make into rolags. The fibres are quite short, similar to cotton.
Spin in the same way as you would cotton but S-spin. The nettle fibres can be spun while they are still quite coarse - when the finished yarn is boiled with soap it will become softer.
Also hitting the hank with a hammer or mallet works to make it softer.
Blend the hard woody bits (left over in the cloth after stage 5) to a pulp and use this to make paper sheets and vessels.
©Birte Ford 2007
For a more detailed description and for other retting methods see my book Yarn from Wild Nettles: A Practical Guide . (For delivery in UK & Europe Amazon.co.uk and in UK bookstores ISBN-10: 1999712501.