mrjayd, one little trick i learned to tell if you're overwatering is to put a softwood stick(or kebab stick) deep into the corner of your pot, obviously being careful of the roots. Leave it for 20 minutes or more, if it's wet when you pull it out then you've overwatered it. I use this technique with all my trees and leave the sticks in all the time now and only water the trees when the stick is starting to get dry.
Seems to work for me
Dacros