There is one product that I have used that I really have come to like when dealing with foliage type stuff, Hob-E-Tac Adhesive it is from Woodland Scenics and it works similar to contact cement except you only need to apply to one piece rather than both. Apply it, let is set up for about 15 min. and then stick the foliage to it. After diluted white glue through a spray device and thats about it.
I headr from my brother (jurjen aka Jurjen) that I put a lot of wood-glue on my dio and then put a lot of that stuff on it. And as is it, pull all the stuff what is loose away. I think that I also making trees with this ''technic''