Arborvitae (Thuja) is a popular evergreen tree frequently used for creating dense privacy screens and hedges due to its fast growth and year-round foliage. Fall is a definitive and opportune time for successful establishment. Planting in autumn provides biological advantages that set the stage for robust growth the following spring. With proper techniques and winter preparation, Thuja can transition seamlessly into its new location during the cooler months.
Why Autumn is Ideal for Arborvitae Root Establishment
Fall favors root development over canopy growth in newly planted evergreens. Cooling air temperatures signal the plant to reduce energy expenditure on producing new foliage. This biological shift minimizes transplant shock, which is a major risk during the heat of summer.
The soil retains warmth accumulated throughout the summer months. While above-ground growth slows, the warm soil encourages the root system to continue development and expansion into the native soil. This allows the plant to anchor itself and establish a strong foundation before the ground freezes solid. Trees planted in the fall focus energy on new foliage growth in the spring, having already established their roots.
Optimal Planting Window and Technique
The ideal window for planting Arborvitae is approximately six to eight weeks before the average date of the first hard freeze in your region. This timeframe allows roots to grow and spread before the soil temperature drops below the point of active development. Planting too late increases the risk of winter damage because the plant has not had enough time to anchor its root system.
Planting requires specific attention to the root ball and hole dimensions. The hole should be dug two to three times wider than the root ball diameter, but only as deep as the root ball itself. This shallow, wide approach encourages lateral root growth, which is beneficial for stability and nutrient uptake. Before placing the tree, gently score or loosen the outer roots, especially if container-grown, to prevent circling and encourage outward growth. Ensure the root flare—the point where the trunk widens at the base—sits slightly above the surrounding soil level to allow for settling and prevent stem rot.
Crucial Steps for Winter Survival
The most common failure for fall-planted evergreens is winter desiccation, caused by a lack of sufficient moisture during the winter months. Newly planted Arborvitae requires deep soakings in the weeks following planting, continuing until the ground is completely frozen. This pre-freeze saturation ensures the plant’s tissues are fully hydrated, providing a moisture reserve when roots can no longer absorb water from the frozen soil.
Mulching is an important step, as it helps regulate soil temperature and conserve moisture. Apply a layer of organic mulch, such as shredded bark, two to four inches thick around the base of the tree. Use the “mulch donut” method, leaving a six-inch ring of space adjacent to the trunk to prevent moisture buildup that can lead to disease or rot.
In exposed locations, protection against harsh winter winds and sun scald is necessary. Arborvitae are susceptible to winter burn, which occurs when foliage loses moisture faster than frozen roots can replace it. Simple physical barriers, such as burlap screens attached to stakes, can be positioned on the windward side to shield the plant from drying winds. Columnar varieties may benefit from having their branches loosely tied together to prevent breakage from heavy snow or ice.