The green buds that emerge with the first warm days of April cannot help but inspire winter-weary gardeners, so it’s no wonder that spring is the most popular season for planting. But fall is the best time to plant most trees, shrubs, and hardy perennials.
The hot dry summer weather that follows closely on the heels of spring causes plants to lose water through their leaves due to transpiration. New plants can better survive the stresses of transplanting in autumn’s cooling temperatures and summer-warmed soil. Precipitation tends to trend upward in the fall, so less supplemental water is needed. When properly timed, fall planting allows plants to develop solid root systems, preparing them for vigorous growth in the spring. Perhaps the most practical reason to enhance your landscape in the fall is that most nurseries and garden centers discount stock later in the season.
Knowing when, what, and how to plant in autumn is key. Although it is possible to plant until the soil can no longer be worked, September through October is the best time to plant trees and shrubs. Six weeks is considered adequate time to establish strong roots before the ground freezes and trees and shrubs enter dormancy. Aboveground growth ceases when the air temperature drops below that of the soil, but roots continue to develop until soil temperatures are below 40 degrees.
Deciduous trees and shrubs are more suitable for fall planting than evergreens. Evergreens lose water through their leaves through transpiration year-round, making them especially susceptible to winter damage from strong dry winds, sunscald, and temperature fluctuations. Pines and spruces are generally hardy enough for fall planting, but some narrow-leaved evergreens, including hemlocks and yews, and most broadleaved evergreens such as rhododendrons and arborvitae perform better when planted in spring.
Alder, apple, buckeye, crabapple, elm, hawthorn, honeylocust, Kentucky coffee tree, linden, maple, and sycamore are among the deciduous species well-adapted to fall planting. Ginkgo, magnolia, sweetgum, tuliptree, willow, and most oaks are slower to establish strong root systems and are best planted in spring. Most deciduous shrubs, such as forsythia, hydrangea, lilac, and witch hazel, can also be successfully planted in the fall. All bare-root trees and shrubs should be planted in late winter or early spring.
Fall planting does require some special attention. Select plants that appear healthy and have no signs of disease or insect infestation. Container-grown plants may be pot-bound after a full season at the nursery. Loosen and unwind circling roots or cut slits in the sides and bottom of dense root masses to encourage the roots to spread outward and establish in the new soil.
Water new plantings thoroughly and continue watering until the ground freezes. New trees need a weekly deep root soaking, and all plants need about an inch of water every week until the ground is frozen, even after leaf drop. Winter freezing and thawing causes soil to repeatedly expand and contract, which can cause plants and shrubs to heave out of the ground. Cover the root area of new plants and trees with 3-4 inches of mulch to help regulate soil temperatures, being sure to pull it away from direct contact with bark and stems. Check periodically for any cracks that appear in the soil and refill them. If wildlife is a problem, hardware cloth barriers can protect tender trunks and stems from damage by mice, rabbits, voles, and deer.
For more information about how to select and plant appropriate trees, shrubs, and plants for your landscape, go to the Penn State Extension website, extension.psu.edu.
Maureen Karl is a Penn State Master Gardener. This volunteer program supports the outreach mission of Penn State Extension. Have a gardening question? Email it, along with photos, to the Garden Hotline staffed by the Penn State Extension Master Gardeners of Allegheny County at alleghenymg@psu.edu.
This educational blog is a series of informative articles from the Penn State Master Gardeners volunteers plus news concerning the group and their activities. For more information, click here.
