Question
My mother-in-law has a very large (ten feet+) rose of sharon bush that we need to move while the current mobile home is being replaced. In a previous answer I was told that the bush had to be trimmed back to make it easier to handle. But what I want to know is how big should the root ball be to prevent the bush from dying? We are going to use a tractor to dig it up, so I want to make sure we dig deep enough, and since we are going to use a tractor to dig it up do we still need to trim it back severely?

Answer
Dear Lisa,

  My, what an undertaking--a fragile one, indeed!  I'm going to refer you to this website that deals with transplantion of trees.  I really agree with the size of ball you will need to dig out.  I wouldn't go any smaller than they say.  It's better to be safe than sorry!!.
 The best time is in early spring.  You can trim it back in the late fall so it isn't so large on the top.  All growth comes on new wood on the Rose of Sharon.  If there are limbs that are very large-prune them out or if there are crossed ones, prune them out.  The rule of thumb is not to prune more than 1/3 of the shrub.

http://landscaping.about.com/cs/shrubsbushes/ht/transplanting.htm

Sijka