Fall is one of the best times to plant new trees. Cool season planting allows for good root development, as long as there is adequate moisture. There may be less stress from heat and drought in cool conditions. Woody trees and shrubs may take as long as 3 years to recover from transplanting and become established.
When trees and shrubs are moved from one planting site to another, or out of containers into the landscape, they experience stress that may affect root establishment. Stress may be the effect of handling, wounding, poor site selection, poor site preparation, or poor soils, and transplant shock may occur. Plants that suffer transplant shock may show dieback, wilt, marginal scorch, chlorosis, small leaves, leaf drop, suckers or water spouts, slow growth, or die.
When transplanting trees you can add watering bags to help you get the correct amount of water to the trees.
(Information from University of Delaware Cooperative Extension)