The Idea Room has a link (sorry for the link to a link :) to the tutorial for this. When I picked up the urn antiquing last summer, I was originally going to make and put a moss ball in it. (I never did get that done!) Instead, here is a quick felt topiary.
The only changes I made...
I only did the top half o the ball, knowing I was going to put into this urn and
I used my die cut machine to cut all the circles.