Site Selection and Timing
Pick a location that perfectly suits the water needs, sunlight requirements and mature size of the tree. Meet these needs to a T; don't simply assume the tree can handle the fact that a downspout will pour onto its roots. Trees add height to the landscape as a permanent landscape feature. Research and accommodate the chosen type of tree to limit future stress or the need for removal because the tree simply isn't thriving in the location.
Remember that planting a tree in the spring allows acclimation during the peak growing season. Plant in early to late spring when tree still feature closed buds. The cooler soil temperatures during spring assist the plant in adjusting to the new location before the heat of summer.
Unlike shrubs and flowers, it's best to disturb the soil around a tree planting site as little as possible. This doesn't mean you can't turn over the soil. Avoid adding excessive amendments at planting time. If you have poor quality soil, consider delaying the tree planting to the following year. Get a soil analysis and amend the soil properly. The year waiting period will allow the organic additives to break down to improve the soil. If adequate soil exists, grab a spade and turn over a 6-foot area around the planting site to a depth of 10 to 12 inches. Loosening the soil makes it much easier for sucker roots to travel through the dirt as the tree becomes established.
Digging the hole
Planting depth is crucial for trees because the optimum goal lies in avoiding sinking of the root ball. Imagine the sideways view of a large mixing bowl. That's exactly how you want to dig the tree-planting hole. Dig to a depth just slightly smaller than the root ball and don't loosen the soil at the bottom of the hole. Width should be 2 to 3 times time size of the root ball with sloping sides (like the side view of the mixing bowl).
Prepping the Tree
Trees have a critical point called the root collar. The root collar refers to the point where the root system starts. This could be hidden in the soil of a transplant container or wrapped up in burlap. Don't assume the top of the root ball marks the point of the root collar. It doesn't. Look for the area where roots first flare out from the trunk to travel horizontally. Bingo - the root collar. Some nurseries bury plants well above the root collar. Remove all of this soil and clean the plant as much as possible before transplanting. Cut away plastic planting containers and all twine or wire holding the root ball. Burlap should remain around the root ball when moving to the planting hole and folded down into the bottom of the planting hole.
Place the tree carefully into the planting hole with the main truck placed in a vertical position. The root collar position should lie EVEN or slightly above the surrounding soil level. Pour soil around the bottom of the hole first to fill in around the root ball. Firm the soil carefully with your hands. Continue adding soil at 4 to 6 inch intervals and firming between each addition. Do not step down on the soil to compress it since you may snap tree roots especially those of a bare root plant.
No matter how much you're tempted, don't add soil amendments to the tree planting hole. Skip the fertilizer as well. Don't pour root stimulants into the hole either to increase the speed of growth. Finally, don't prune a young tree at all unless you're trying to remove dead foliage. The gardener's job for a fledgling tree is to provide enough water to keep the soil evenly moist as the tree acclimates.