Take It Out of the Pot
With a container-grown tree, the main advantage to planting in the fall is to reduce the summer water stress, which isn't typically severe in humid Alabama. Roots begin to grow out into the soil in fall, and continue growing, although more slowly, through the winter. The greater root mass helps them withstand the need for greater water needs once warm weather arrives. Container plants can be planted year-round where the soil doesn't freeze, but if you plant in spring or summer, be prepared to water more frequently until the roots grow out.
Unwrap the Roots
Trees are also available as field-grown plants that are dug up and the roots wrapped with burlap. The plants should be kept in the burlap for several months so new roots grow to replace some of those destroyed by digging. Growers water the plants so that roots grow to penetrate the burlap. Some balled-and-burlapped trees do best when transplanted in early fall at least four weeks before soil temperatures drop below 40 degrees Fahrenheit. Many deciduous trees begin active root growth then, allowing better establishment.
When Roots Are Bare
A relatively inexpensive way to add trees to your landscape is to buy them when they are fully dormant as bare-root trees. Growers dig them from the field and remove the soil from the roots. Moist packing materials such as sawdust keep the roots from drying out during shipping. Many deciduous fruit trees and cold-hardy ornamentals are available bare-root. The planting time is limited from about November to March, when the trees are in dormancy. The dormant period is longer in northern Alabama. When you receive a bare-root tree, unpack it and soak the roots in water for about 24 hours, and then plant it directly in the ground or into a container.
Some Exceptions to Fall Planting
Tree species vary as to when their roots are actively growing. Live oak trees (Quercus spp.) have best root regeneration during July and August when new shoots are finished elongating, as do magnolia (Magnolia grandiflora) and elms (Ulmus spp.). Growers dig them in summer for better root establishment, so if you want to plant them in fall, make sure they are sufficiently hardened off. Some balled-and-burlapped trees such as filberts (Corylus spp.) transplant best in late winter and spring when the roots begin active growth. Live oaks are hardy from USDA zone 8 through 10, and magnolia from USDA zone 7a to 10a. Chinese elm (Ulmus parvifolia) grow in USDA zones 4 through 9 with filberts hardy in USDA zones 5 through 9.