Generally, you should prune around 20% of an apple tree’s growth—and never more than 30%. This means that if you have a severely overgrown tree, it can take a few seasons to prune it back enough to produce the healthiest fruit. 

If you’re dealing with a newly planted or juvenile tree, hold off on pruning beyond the initial shaping. Wait at least a couple of seasons into fruit production since pruning can increase the number of water sprouts and unproductive foliage.

It depends on the type of tree. Typically, late spring on the cusp of winter is ideal for trees about to emerge from dormancy and produce new buds. That said, late fall is ideal for certain deciduous trees prone to bleeding sap. Avoid trimming trees in early spring, when they’re prone to disease.

Completely topping a plum tree is a risky business. Cut too much, and you’ll kill your tree. That said, you do need to trim the top of your tree to encourage bushy growth, maintain your tree’s vase shape, and limit size. 

A plum tree's central leader (or trunk) should never extend more than 3 feet above the highest branch. When you first plant your tree, cut the central leader so it’s 2 to 3 feet tall. As it grows, cut it back 12 to 20 inches until it reaches its desired height. Never prune more than one-third of the new growth.

It’s possible to transplant trees as tall as 50 feet when an experienced tree planting service uses the right equipment. However, a tree with a trunk larger than two or three inches in diameter needs to be handled by a professional in order to yield successful transplanting results. Consulting a tree planting professional is the best way to tell if your large tree can be safely transplanted.