At The Morton Arboretum, we plant specimens in our botanical collections in both the spring and fall. With the usual generous spring rains in the Chicago area and the long growing season ahead, most people think of spring as the preferred planting season. Unfortunately, sometimes that generous rainfall prevents us from getting into the site as it makes the soil too wet to plant. Also, in many years, we have a "shortened" spring season and jump right into the hot, dry summer. It is hot, dry conditions beginning too rapidly that can injure newly-planted specimens.
So fall season planting (mid-August through mid-October) offers many advantages that may outweigh spring planting. Transpiration is low and root generation potential is high. The temperatures are typically moderate to cool, and are easier on the plants so there is less chance for the trees to be stressed by extreme heat. The fall moisture (rains) helps the trees and shrubs establish their root systems. When the air temperatures are cooler than the soil, new root growth is encouraged without new top growth. The result is a stronger, better developed root system for the next spring when the plant begins to grow. Mulching with wood chips helps retain the soil's required moisture.
If you wait too long into the fall season (November - December) to plant, you run the risk of poor root growth and increased failure rate. Conifers, in fact, need a slightly earlier start than hardwoods, preferring the warmer soil temperatures of the summer to early fall.
Some slow to establish species are best planted in spring. These include bald cypress, American hornbeam, ginkgo, larch, magnolia, hemlock, sweetgum, tuliptree, and willow. Also broadleaved evergreens such as rhododendrons and narrow-leafed evergreens such as yews prefer spring planting. In general, plants with shallow, fibrous root systems can be planted easier in the fall than those with fewer, larger roots.
Trees that can be successfully planted in the fall include alder, ash, buckeye, catalpa, crabapple, hackberry, hawthorn, honey locust, elm, Kentucky coffee tree, linden, maple, sycamore, pines, and spruces. Most deciduous shrubs can easily be planted in fall.