Curtains should not be included in your green recycling bin. Good quality curtains can be donated to a local charity shop. They may be suitable for reuse through a local reuse network such as Freecycle or Freegle. There are now a large number of reuse groups on Facebook.
Otherwise, curtains can be included in the clothing banks at your local Household Recycling Centre. Please make sure they are clean but even torn curtains can be included.