Arborvitae (Thuja species) are popular evergreen shrubs and trees, often used for privacy hedges due to their dense foliage and upright growth habit. While the cooler weather of early spring or fall is generally recommended for planting to allow roots to establish, you can successfully plant container-grown arborvitae in the summer with specific, careful measures. The success of summer planting hinges on mitigating the intense heat and water stress that occurs during the warmer months. Planting balled-and-burlapped (B&B) stock is significantly riskier, but container-grown plants can survive if they receive immediate and consistent attention.
Why Summer Planting Creates Severe Stress
Planting arborvitae during the summer exposes them to two physiological dangers: transpiration overload and root shock. As an evergreen, the plant constantly loses water vapor through its foliage, a process called transpiration, even in the heat. High temperatures and low humidity increase this rate of water loss dramatically, demanding a constant supply from the roots to replace the moisture. The problem is that the newly disturbed, compromised root system cannot absorb water fast enough to keep up with the foliage’s demand. This mismatch between water loss and absorption is what causes the classic browning and dieback often seen in summer-planted evergreens.
New root growth, which is necessary for establishing the plant, largely stalls in high soil temperatures. This makes the plant unable to quickly repair the damage or expand its water-gathering network.
Essential Site and Root Preparation
To minimize the immediate stress of transplanting, it is helpful to plant in the coolest part of the day, such as the early morning or evening. The planting hole must be dug wide, two to three times the width of the root ball, but no deeper than the root ball itself. The goal is to provide loose, welcoming soil for the roots to expand horizontally, as arborvitae naturally have shallow, spreading root systems.
Before placing the plant in the hole, the root ball must be thoroughly saturated with water. For container-grown stock, it is crucial to inspect the roots for circling or girdling; gently scoring or teasing out these compacted roots will encourage them to grow outward into the surrounding soil. Backfilling the hole should be done with the original soil, possibly amended with a small amount of compost or organic material to help with moisture retention. The root flare, which is the point where the trunk widens at the base, should remain at or slightly above the finished grade to prevent the trunk from sitting too deep, which can lead to root rot.
The First-Month Watering Strategy
The first four to six weeks following summer planting are the most important period for survival and demand a consistent watering schedule. Immediately after planting, the tree requires a deep soak to settle the soil and eliminate any air pockets around the roots. This initial saturation is followed by a period of consistent, frequent watering to ensure the root ball remains moist, but never waterlogged.
During the hottest summer weeks, newly planted arborvitae often require deep watering every day or every other day, especially when temperatures exceed 70 degrees Fahrenheit. The soil moisture should be checked by probing about six inches down, just outside the root ball, to confirm the soil is moist and not just dry on the surface. A slow, deep application method, such as a soaker hose or drip irrigation, is recommended to deliver water directly to the shallow root zone without waste.
Applying a two- to three-inch layer of organic mulch, such as shredded bark, over the planting area is also necessary. Mulch helps to regulate the soil temperature, preventing the root zone from overheating, and significantly reduces moisture evaporation. It is important to keep the mulch ring several inches away from the trunk’s base to prevent moisture from accumulating against the bark, which can encourage disease. Browning tips or wilting foliage are clear signs of water stress, indicating that the watering frequency or duration needs to be increased.