The training of young trees can be highly beneficail to the long term structure and health of a tree. The planting of new trees can be stressful enough on them though, you do not want to immediately start pruning after planting (aside from dead, damaged or diseased material). The tree will need time to estabilish itself and all of the foliage is helping to do this. It is typically recommended to wait until the 3-5 year mark, depending on how vigorous the tree is growing. If you are not sure when to start, a certified arborist is a great tool to use. We want to help insure that the tree has a long and healthy life!