Take advantage of a plant's natural winter dormancy to get those new trees and shrubs in the ground. Most trees, shrubs and plants go dormant during the coldest months of the year, with little in root or foliage growth occurring from Dec-Feb. It's the perfect time to plant your new garden, privacy screen, or add specimen trees to your landscape.
In addition to the natural lull in growth, winter is the perfect time to plant because the ground tends to stay moist. This allows the new plant's soil rootball to better integrate with the native soil adjacent to the rootball. The small air gaps that will occur during the planting process will have a chance to disperse and rise through the soil as rainwater leaches down. The plant will "settle in" better over the winter months, and come Spring, you'll see faster and more vibrant growth.
Last, planting trees and shrubs in the winter will usually require far less irrigation as the plants establish themselves. The colder temperatures mean rainwater evaporates more slowly, leaving the ground damper for longer periods of time.
