The Emerald Green Arborvitae (Thuja occidentalis ‘Smaragd’) is an evergreen valued for its dense foliage and columnar shape. Successfully establishing this shrub depends heavily on providing the roots with the best environment for growth immediately after transplanting. The timing of planting is the most important factor influencing how quickly the tree can settle into its new location and develop a robust root system.
Optimal Planting Seasons
The best conditions for arborvitae root development occur when soil temperatures are moderate. Early spring is an ideal time, beginning as soon as the ground thaws and becomes workable, but before the onset of summer heat. This timing allows the plant to focus energy on growing roots while the cool air temperature reduces moisture demands on the foliage.
The second optimal window is early fall, approximately six weeks before the first anticipated hard frost. Planting during this cooler period stimulates root growth in the still-warm soil without encouraging excessive new growth on the branches, which would be vulnerable to winter damage. Cool, moist soil promotes root elongation and allows the plant to anchor itself before facing temperature extremes.
Avoiding High-Stress Planting Periods
Planting should be avoided during periods when environmental factors place stress on the root system, specifically mid-summer and deep winter. Attempting to plant from June through August subjects the evergreen to intense heat and high rates of water loss through transpiration. This combination forces the plant to draw excessive moisture from the soil, which can rapidly lead to severe root stress and desiccation.
Deep winter planting carries risk, primarily due to frozen ground and potential desiccation injury, often called winter burn. While the plant may be dormant, the frozen soil prevents the roots from taking up water to replace moisture lost from the leaves due to dry winter winds and sun exposure. This inability to replace lost moisture causes the foliage to dry out and turn brown.
Site Preparation and Soil Needs
Site preparation begins with selecting an area that receives adequate sunlight, preferably full sun to partial shade. Arborvitae thrive best when they receive at least six hours of direct sunlight, which encourages denser, more vibrant foliage. The plant requires well-drained soil because it is prone to root rot if the roots remain constantly saturated.
If the native soil is heavy clay, it should be amended with organic matter like compost to improve its structure and drainage capabilities. When preparing the hole, dig it to be two to three times wider than the root ball, but ensure it is no deeper than the height of the root ball itself. Ensure the root flare rests at or slightly above the final soil line to prevent water accumulation near the trunk.
Immediate Aftercare
Immediately following placement in the prepared hole, the arborvitae requires deep watering to settle the soil around the roots and eliminate any air pockets. This initial soaking helps the plant connect with the native soil and reduces transplanting shock. After the water has fully absorbed, apply a two-to-three-inch layer of organic mulch around the base of the plant.
Mulch helps retain soil moisture, regulates temperature, and suppresses weed growth that competes with the establishing roots. Keep the mulch pulled back a few inches from the trunk to prevent moisture buildup, which can lead to rot and create an environment for pests. Consistent monitoring and supplemental deep watering, especially during the first full growing season, will ensure the roots establish fully.