Plants that have been grown in containers should be taken out of the container and the roots should be inspected to see that they have not become pot bound. If the roots are pot bound, make four vertical cuts about one inch deep on opposite sides of the root ball, then tease the roots free. You may find it necessary to repeat this procedure along the base of the root ball.
It is not necessary to add amendments to the backfill unless the soil is particularly sandy or gravelly. In exceedingly fast draining soils such as these, it may be beneficial to add organic matter in an effort to boost water retention and provide nutrients for new transplants. Heavy clay soils should be loosened in a wide area around the plant to prevent the development of girdling roots.
Generally speaking, it is best not to fertilize during the first season. New plants should be allowed a period of time in which to establish themselves and become acclimated to the site. In the case of field dug material, you may mix a bit of rock phosphate or bone meal into the backfill to encourage new root growth. High nitrogen fertilizers should be avoided particularly in the case of field dug plants, as it will encourage top growth that the root system cannot adequately support. Never allow synthetic fertilizers to come in direct contact with the roots of your plants.
Add the backfill slowly and water your plants in well, making sure that there are no air pockets in the soil around the roots. In the case of trees and shrubs, a two or three inch layer of mulch should be applied to the surface of the soil after planting. The addition of mulch will keep the roots of the plant cooler while reducing moisture loss. Be sure to keep mulch away from the trunk of the plant to prevent the possibility of rot or insect damage.
Research indicates that staking your tree(s) is not necessary except in areas favoring strong or persistent winds. It has been suggested that some sway in newly transplanted trees may actually help stimulate root growth.
Water is critical. Failing to provide adequate water for new transplants may stress or kill the plant. Try to insure a good soaking twice a week for the first several weeks and then once a week thereafter, regardless of whether or not it rains in the interim. Plants should be put in the ground as soon as possible after purchase. If you must put off planting for a few days, be sure to store your plants out of direct sunlight and water them daily.