I'll let you know how it goes. But I will tell you that cardboard, newspaper and mulch won't do the trick. It will help them be nice and healthy so they can really get to spreading though.
My plan is concrete pipes. Some of them are very wide so if I can get some that are long enough I can upend them where I want the trees and then fill them with dirt and that will be my wild plum orchard lol. Then all I have to do is make sure to not let any of the fruit rot in place and I've got it made.