I don´t have enornous amount of plants to swap but I have started a to experiment taking cuttings and atleast silver colored Artemisia seems to be making new roots. -How exciting is that? :) I will try a cutting from a Hebe as well and these will be ready for swap any time this spring, provided that you are similar kind of spirit who just loves to try new things and not get upset if not all cuttings will become a great success. In exchange I am currently looking shade tolerating plants -hostas for example- but tbh.. anything goes. Apart from tomatoes and other veg. And no.. they need not be mature and well established. I also have a white hybrid rose bush in a container ready to be swapped to just about anything (dwarf conifer or a small shrub would be a treat!) . It used to be 1.5m tall tree growing from the ground but we cut it short and its now having a new life (making blooms too) in a temporary container. We have black spots in all our rose trees -even the ones growing to 4m height- so this little rose will most likely be affected as well.