Is it safe to plant trees and shrubs in the fall?
Broad-leaved and needle-leaved evergreens are best planted in the early fall, up until around October 1 in our area, so that they can become more easily established before winter sets in. Deciduous trees are best planted after leaf drop, around October 15 until December 1, before the ground freezes. Be sure planting conditions are suitable; the ground must not be excessively wet or frozen. Water well after planting and apply a mulch around the planting pit. It is important to note that certain tree species are really best planted in early spring: Prunus (ornamental cherries), Quercus (oaks), Liquidambar (sweet gums), Crataegus (hawthorns) and Magnolia (magnolias).
Courtesy of the NYBG Plant Information Service