@JV
I got to thinking about your tree vs my tree and I think you are working with a tree with a larger root mass than mine and it is already programmed to grow taller than my tree. I started with a young tree and never allowed it to grow large.
I would not know how to begin to make a tree that has a more mature root mass stay small.
NGA does have a TREE AND SHRUB forum. I think you might get a better answer if you posted your question there.
http://garden.org/forums/view/...
