Depending on the type of tree, you may need to protect it during its first year or two if it is sited in an open area exposed to prevailing winds.
Staking: If it has a heavy canopy or a small, loose rootball or is large or bare root, a newly planted tree may need temporary staking. If it seems to be necessary stake trees loosely and for only 6 months to a year. Tree trunks thicken and strengthen faster when they can move freely. Drive two or three stakes into the soil equidistant from the tree and each other just beyond the root zone. Use a commercial tree staking product or loop wide, soft straps of cushioned rope or cloth strips around its trunk and tie one to each stake. Check frequently to be sure it is not rubbing the tender bark.
Screening: An alternative to staking is to erect a windscreen. Fasten a length of burlap, snow fencing or commercial garden fabric such as shade cloth, or white polyspun floating row cover to posts on the windy side of the tree about 6 feet from the trunk to divert strong wind yet allow air circulation around exposed trees, especially evergreens.
Heat and Sun Protection
Newly planted or transplanted trees that have leaves, such as evergreens, are in danger of losing too much moisture through transpiration from the foliage because of transplant shock. This is especially serious if they are planted in the sun in broad daylight. To minimize this stress, coat the foliage beforehand with an anti-transpirant spray.
Certain young trees such as ornamental cherries are vulnerable to sunburn on their tender bark which causes it to crack, jeopardizing their health. Wind tree wrap, natural burlap or kraft paper as a sort of bandage around the trunk from the soil level to the lowest branch to protect it from sunscald. Recent research suggests that wraps retard the establishment of trees and may also provide a habitat for insects or disease and rot. So use them only during the spring or summer before their foliage grows to shade them on trees planted near heat and light reflecting paved areas. Remove tree wraps in spring to allow for new growth.
The health and longevity of all trees, but especially newly planted, young ones, is improved if the soil they grow in is improved. Do all you can to assure that their soil is rich in organic matter, free from compaction by rain, foot traffic and equipment and free of competing weeds and turfgrass.
Maintaining a year round 3 or 4 inch layer of mulch will significantly improve the soil over time. Use dried grass clippings, wood chips, a commercial bark product or chopped leaves in the fall from your mulching lawnmower. Spread them over the tree root zone out as far as the branch tips (the dripline) or farther. Do not pile the mulch against the trunk. In the winter mulch insulates the soil against extreme temperature fluctuations--alternate freezing and thawing--that sometimes disturb tree roots and heave those of newly planted small trees out of the soil. Replace depleted mulch regularly.
Protection from Pest Animals
The tender bark of young trees is often damaged by critters. Both deer and rodents, such as mice and voles, chew on it during the winter when other food sources are scarce. Deer also rub up against young trees, abrading their bark.
Surround the thin trunks of newly planted or transplanted young trees with a commercial tree shelter product. These tough covers or translucent plastic sleeves fit loosely around whips and saplings as a barrier to protect the tree bark. Shelters also create a "greenhouse" environment which research has shown actually increases trunk growth rates in the initial years. Check periodically to make sure that trunk guards are not too tight.