Arborvitae (Thuja) are popular evergreen conifers often used for privacy screens. While typically planted in the ground, these versatile plants can successfully thrive in containers, allowing for flexible placement on patios or decks. Success requires specific adjustments to their environment and maintenance schedule compared to in-ground planting. This approach demands careful attention to cultivar selection, root space, and year-round moisture management.
Choosing the Right Cultivar
Selecting the appropriate variety is the most important initial decision for long-term container success. Standard arborvitae varieties, such as the full-sized ‘Green Giant’, possess aggressive root systems and substantial mature heights that quickly overwhelm a pot. These large shrubs become root-bound and stressed, demanding frequent, impractical repotting.
The goal is to match the plant’s ultimate genetic size with the physical constraints of a container. Focus instead on naturally dwarf or slow-growing cultivars to minimize maintenance and maximize the plant’s lifespan in the pot. Compact, globe-shaped forms like ‘Tiny Tim’ or ‘Hetz Midget’ are excellent choices for smaller spaces.
Columnar varieties, such as ‘Emerald Green’ (‘Smaragd’), can also be used, but they require consistent root and canopy pruning to manage their size. Pruning the roots every two to three years helps maintain vigor and prevents the plant from becoming too top-heavy. Choosing a variety that naturally stays small reduces the frequency of this labor-intensive maintenance.
Essential Pot and Soil Requirements
The container must be correctly sized to accommodate the arborvitae’s root ball and offer ample room for future growth. Select a pot that is at least twice the diameter of the existing root ball, or two sizes larger than the current container. Proper drainage is a necessity, meaning the container must have functional drainage holes to allow excess water to escape.
Pot material affects maintenance. Porous terracotta or ceramic pots allow moisture to evaporate quickly, requiring more frequent watering. Non-porous plastic or glazed containers retain moisture longer, which reduces watering frequency but increases the risk of root rot if the soil composition is incorrect.
The soil mixture needs to be lightweight, highly aerated, and fast-draining to prevent compaction that suffocates roots. Never use heavy garden soil, which quickly compacts and impedes drainage and oxygen exchange. Use a high-quality commercial potting mix, ideally amended with materials like perlite, pumice, or pine bark fines. These amendments create necessary air pockets, improve structure, and facilitate the rapid movement of water through the container.
Routine Care and Watering
Moisture management is the most challenging aspect of maintaining containerized arborvitae, as the restricted soil volume dries out much faster than ground soil. The danger lies in both extremes: allowing the root ball to completely dry out causes irreversible damage, while consistently soggy soil leads to fungal issues and root asphyxiation.
To determine watering needs, use the “finger test” by inserting a finger about two inches deep into the soil near the plant’s edge. If the soil at that depth feels dry, water the plant until it flows freely from the drainage holes. During hot, windy summer months, this may need to be checked daily, especially with smaller or terracotta pots.
Arborvitae perform best in locations that receive full sun for at least six hours per day; however, some afternoon shade can prevent foliage burn in extreme summer heat. Inadequate light causes the foliage to thin out, reducing the plant’s dense appearance. Rotate the pot occasionally to ensure all sides receive consistent light exposure.
Fertilization should be approached cautiously, as the plant’s growth is limited by the container size. Use a slow-release, balanced granular fertilizer, such as a 10-10-10 formulation, once in early spring as new growth begins. Over-fertilizing encourages excessive, weak growth and can cause a buildup of salts in the restricted soil volume, potentially damaging the roots.
Ensuring Winter Survival
The primary threat to container evergreens in cold climates is the exposure of the root system to freezing and thawing cycles, not the cold air itself. Roots in a pot lack the insulating buffer provided by the surrounding earth, making them susceptible to freeze damage when temperatures drop below freezing.
To protect the roots, move the container to a sheltered, unheated location once consistent freezing temperatures arrive. Suitable options include an unheated garage, shed, or a protected spot against a wall of the house that blocks wind. Grouping multiple pots together offers a collective insulation benefit, helping to keep the root zones slightly warmer.
Another protective measure is to insulate the container walls by wrapping them with burlap or bubble wrap, and applying a thick layer of mulch over the soil. While dormant, the roots still require moisture, especially during dry winter periods without snowfall. Check the soil every few weeks and provide a light watering on days when the temperature is above freezing to prevent winter desiccation.