Many deciduous trees are sold bare-root during the dormant season from late fall through early spring. Deciduous trees as well as conifers and broad-leafed evergreens may also be sold balled-and-burlapped from early fall into the following spring, or in containers throughout the year.
All trees--even the drought-tolerant kinds--need regular water during the first several years after planting, until the roots have grown deep enough to carry the plant through dry periods. Once established, however, most trees require only infrequent irrigation.
Regular fertilizing, too, is needed for a few years after planting. By ensuring a nitrogen supply for the springtime growth surge, you'll encourage young trees to get established quickly. Once a tree is well settled in, though, it may grow satisfactorily with no further feeding--and in fact, fertilizing a tree that continues to put out healthy, vigorous new growth is a waste of both time and fertilizer. But feeding may be in order if a tree's new growth is weak, sparse, or unusually pale, or if the tree has a fair amount of dieback that can't be ascribed to over- or underwatering.
Forming a strong tree trunk
Young trees develop a strong trunk more quickly if their lower branches are left in place for the first few years after planting; these branches also help shade the trunk. During this time, shorten the side branches only if they become too long or vigorous, pruning during the dormant season or just before spring growth begins. Once the trunk is at least 2 inches thick, begin removing the lower branches gradually, over a period of several years.
Staking your trees
A young tree will develop a sturdier trunk if it grows unsupported and can sway in the breeze. Stake it only if it is planted in an extremely windy location or if the main trunk is too weak to stay upright on its own. Use ties that won't bind or cut into the bark, such as wide strips of canvas or rubber; fasten each tie around the tree and both stakes in a figure-8 pattern, as shown below. The tree should be able to move an inch in either direction.
To figure out where to attach the ties to a weak trunk, run your hand up the trunk until you find the point where the top no longer flops over. Cut off the stakes an inch or so above the ties. In a windswept site, a young tree's roots may need anchoring to keep them in firm contact with the soil; use stakes and ties only a foot above ground level for this kind of staking. In both cases, sink stakes at right angles to the prevailing wind. Remove them after about a year or as soon as the tree appears to be self-supporting.
Protecting a young tree's trunk
Wrap the trunk of a newly planted tree to protect it from drying winds, hot sun, freezing temperatures, gnawing wild animals such as rabbits, deer and rodents, and damage from carelessly used lawn mowers or string trimmers. For wrapping, use loosely tied burlap or a manufactured trunk wrapping material. Remove the wrapping after a year, when the bark has become thicker and tougher. (Don't leave it in place longer than this, since it can eventually girdle a trunk.)