Timing is important when you transplant oak trees. Oaks are slow-growing and slow-rooting, which makes transplant timing all the more essential. Once established, oak trees can provide scenery and shade for many years.
Oak trees are difficult to transplant and often do not thrive after being moved. Ideally, plant oaks as seeds or seedlings on the site where you want them to stay. If you must transplant established trees, do so while the trees are still small. Oaks develop deep taproots that make them increasingly difficult to transplant as they mature.
Prune the roots of the tree three to six months before transplanting. Use a spade to cut off the roots 8 to 10 inches deep and 10 to 12 inches from the tree for every inch of trunk width. This allows new roots to begin growing. When the time comes to transplant, dig up the root ball 4 to 6 inches outside the original pruning to capture the new roots. The root ball should be one-half to two-thirds as deep as its width.
Always transplant oak trees in spring; the best time is usually February or March, but the exact time depends on where you live. Transplant the tree while it is still dormant, before buds start growing. Place the root ball in a hole that is more than wide enough to accommodate it; the hole should be no deeper than the root ball.