Size of ball is about 2 1/2 to 3 times of diameter of the tree trunk is good number. Since we hand dig many stock trees and shurbs,and sell much highter price than US or Canada, nuseryman spend more time to mainain nusery stocks.Don't compair with US or canadian standerd of ball size, gingko tree of 15feet to 20 feet we ship bare roots. Most trees in US and Canada are machin dig, not by hand, and physical strengh of nusery workers are also different. Smaller the ball, easeir to handle manualy.
Shape and size of ball is depend on type of tree, type of soil, age of tree, tree's growth habit etc
If root prune have been done the tree previous year, then ball size can be smaller. my 2 cents. .............. yama