In order to have a long and healthy life, trees must be properly planted.
The climate of your area is a major factor when determining the appropriate planting time. Newly planted trees do best when exposed to moderate temperature and rainfall; they need time to root and acclimatize before the weather extremes of summer or winter. Therefore, Spring and early Fall are generally the best planting seasons (depending on your location). In the southern United States, which do not experience an intense winter, planting can take place during the winter months.
While planting different types of trees differs in the details, all trees eventually end up in the ground, and need to start with an appropriate hole.
The most common mistake when planting a tree is to dig a hole that is either too deep or too narrow. Too deep and the roots dont have access to sufficient oxygen to ensure proper growth. Too narrow and the root structure cant expand sufficiently to nourish and properly anchor the tree.
As a rule, trees should be transplanted no deeper than the soil in which they were originally grown. The width of the hole should be at least 3 times the diameter of the root ball or container or the spread of the roots in the case of bare root trees. This will provide the tree with enough worked earth for its root structure to establish itself.
When digging in poorly drained clay soil, it is important to avoid glazing. Glazing occurs when the sides and bottom of a hole become smoothed forming a barrier, through which water has difficulty passing. To break up the glaze, use a fork to work the bottom and drag the points along the sides of the completed hole. Also, raising the bottom of the hole slightly higher than the surrounding area. This allows water to disperse, reducing the possibility of water pooling in the planting zone.
Balled and burlapped (B & B) trees, although best planted as soon as possible, can be stored for some time after purchase as long as the ball is kept moist and the tree stored in a shady area. B & B trees should always be lifted by the ball, never by the trunk. The burlap surrounding the ball of earth and roots should either be cut away completely (mandatory, in the case of synthetic or plastic burlap) or at least pulled back from the top third of the ball (in the case of natural burlap). Any string or twine should also be removed. Backfill soil (combinations of peat moss, composted manure, topsoil, etc.) is then placed in the hole surrounding the tree just to the height of the ball or slightly lower to allow for some settling. Be careful not to compress the back fill soil as this may prevent water from reaching the roots and the roots from expanding beyond the ball.
Container trees (though subject to greater heat and drying conditions than B and B) can also be stored for a brief period of time after purchase as long as the soil in the container is kept moist and the tree stored in a shady spot. The procedure for planting container trees is similar to that for B & B trees. In the case of metal or plastic containers, remove the container completely. In the case of fiber containers, tear the sides away.
Once carefully removed from the container, check the roots. If they are tightly compressed or potbound, use your fingers or a blunt instrument (to minimize root tearing) to carefully tease the fine roots away from the tight mass and then spread the roots prior to planting. In the case of extremely woody compacted roots, it may be necessary to use a spade to open up the bottom half of the root system. The root system is then pulled apart or butterflied prior to planting. Loosening the root structure in this way is extremely important in the case of container plants. Failure to do so may result in the roots girdling and killing the tree. At the very least, the roots will have difficulty expanding beyond the dimensions of the original container. To further assist this, lightly break up even the soil outside the planting zone. This allows roots that quickly move out of the planting zone to be more resilient as they anchor into existing surrounding soil conditions.
Once the tree is seated in the hole, the original soil is then back-filled into the hole to the soil level of the container. Again, remember not to overly compress the back-filled soil especially by tramping it with your feet. Compress gently using your hands instead.
Planting bare-rooted trees is a little different as there is no soil surrounding the roots. Most importantly, the time between purchase and planting is a more critical issue. Plant as soon as possible. When purchasing bare-rooted trees, inspect the roots to ensure that they are moist and have numerous lengths of fine root hairs (healthy). Care should be taken to ensure that the roots are kept moist in the period between purchase and planting. Prune broken or damaged roots but save as much of the root structure as you can.
To plant, first build a mound of earth in the center of the hole around which to splay the roots. Make sure that when properly seated on this mound the tree is planted so that the trunk flare is clearly visible and the crown, where the roots and top meet, is about two inches above the soil level. This is to allow for natural settling. Spread roots out over soil pedestal evenly before filling with soil. See Step-by-step: Tree Planting for a visual guide.