The bigger the better. Prune all roots injured by hand with a sharp tool.
prune them like the end of a straw. Straight accross. Crushed roots
(woody) lead to deacay.

--
Sincerely,
John A. Keslick, Jr.
Arborist
http://home.ccil.org/~treeman
and www.treedictionary.com
Beware of so-called tree experts who do not understand tree biology.
Storms, fires, floods, earthquakes, and volcanic eruptions keep reminding us
that we are not the boss.

"Ook" Ook Don't send me any freakin' spam at zootal dot com delete the
Don't send me any freakin' spam wrote in message
news
I have a dogwood tree that is about 15 feet tall with a trunk of 5 inch
diameter. I would like to move it, but I'm not sure I can without killing
it. How big of a root ball would you think I would have to dig up to move
it without killing it?