I have purchased bulk Heki evergreen trees and then I customize each one like this: I spray each one with clear DullCote to provide the "sticky" and then sprinkle some "Burnt Grass" randomly on them. I then do another spray of clear DullCote to seal the Burnt Grass on. I have done it to the larger trees that have clump foilage on the branches and they look a little boring.
I have also made hedges doing the same thing but I sprinkle on a yellow or red to simulate flowers. The hedges I cut from commercial stripping pads that go on those round floor buffers. You can cut them on a table saw or scissors if you don't have access to a saw.
So you should have no problem spraying your trees and then added the colored foilage to your liking and then a clear coat to seal it on. Good luck. JP
