Take it out in chunks small enough for you to handle. Look at the entire crown as a large pie. Using a sharp axe, chop out triangular pieces. Cut off the inner third of each piece and discard. Re-plant the rest.

You also could use a spade made for this sort of work. There are several, like the King of Spades, which are all steel and extremely sturdy. Use a mill file to put a very sharp edge on it.

Here is a link that might be useful: King of Spades

This post was edited by donn_ on Fri, Apr 18, 14 at 17:22

Or use a reciprocating saw with a long pruning blade to cut it up.