Whether you've purchased a new tree to install in the yard or want to move an existing tree to a new spot, knowing how and when to transplant is key to the plant's success and survival. In general, the best time to transplant is in the early spring, before plants break dormancy, or in late fall, after the tree loses its leaves. Large, established specimens are generally too difficult to transplant, so the gardener should consider carefully where to place a tree, as the spot will likely be its permanent home.
Some species of tree are far more tolerant of transplanting than others. While most young trees have the potential to transplant moderately to very well, species like walnut need special attention and care during and after the transplant process. Trees are extremely vulnerable during the transplant process, since disturbing the root system interferes with the tree's ability to absorb water and nutrients from its surroundings.
Most trees transplant best when they are placed during dormancy, from late fall through very early spring. The root pruning of established trees to be transplanted is accomplished by spading the roots in several places around the tree's drip line; this often helps prepare the tree for the stress of transplanting. Transplanting during spring and early summer frequently kills any new growth and severely slows the growth of the tree. Similarly, transplanting too early in the autumn risks stimulating new growth that can be damaged by early winter freezes.
Soil type and quality are the two most important factors to consider when evaluating a site for tree installation. Poorly drained soils like clay, or compacted soils in urban or disturbed sites, are difficult for new transplants to adapt to, as water tends to pool around the roots and slowly drown the tree. Soils of this type need deep and extensive amendment with organic material and humus to prepare them for tree transplanting. Especially with ball-and-burlap type trees, a hole roughly three times the size of the root ball should be prepared. The hole should have angled sides so that it is wider at the surface than at the base.
Ball-and-burlap trees should be carefully unwrapped and lowered into the hole; center the tree and ensure its trunk is as vertical as possible, with little listing to either side. The roots of bare-root trees should be spread throughout the prepared hole and dirt backfilled into the roots to eliminate void spaces. Containerized trees should be eased out of their pots and the roots gently teased to loosen them, but take care not to break them or handle them too roughly. In all cases, trees should be placed so that their bases are about 2 inches above the ground, allowing for room to settle. Soil, amended with organic material, should be lightly compacted in the filled hole and the upper layer mulched; a depression allows water to pool and gather and can contribute to overwatering stress.
Trees may take a year or more to become completely established in the yard and frequently show little signs of vigorous growth during this acclimatization period. Even during dormancy, however, trees continue to grow their roots. Newly planted trees should be watered deeply but not too frequently, with extra attention given during especially dry or hot weather. Trees should need little to no watering during winter dormancy unless precipitation is lower than average.