The ‘Mr. Bowling Ball’ Arborvitae (Thuja occidentalis ‘Bobozam’) is a dwarf evergreen cultivar known for its naturally dense, spherical shape. This compact shrub typically matures to a height and width of just two to three feet. Its soft, lacy, blue-green foliage maintains its vibrant color throughout the year, offering consistent texture and form to the landscape. The plant’s inherent resistance to common issues and its minimal need for shaping make it a low-maintenance option.
Choosing the Right Location and Planting
The successful establishment of the ‘Mr. Bowling Ball’ arborvitae begins with careful site selection, particularly concerning light exposure. This shrub performs best in full sun, requiring a minimum of six to eight hours of direct sunlight daily. While it can tolerate partial shade, insufficient light leads to sparser foliage and a loss of the characteristic dense, globular shape. In regions with extremely hot summers, providing light afternoon shade can help prevent foliage scorch.
Soil quality must prioritize excellent drainage, as saturated conditions are detrimental to the root system and can lead to root rot. The shrub is adaptable to a variety of soil types, including loamy, sandy, or heavier clay soils, provided water does not pool. A soil pH that is slightly acidic to neutral (ideally between 6.0 and 7.5) supports optimal nutrient uptake.
When planting, prepare the hole to be twice as wide as the root ball, but no deeper than its current depth in the container. Planting the root crown too deep will suffocate the roots and is a common cause of failure. Gently loosen any tightly coiled roots before placing the plant, ensuring the top of the root ball remains level with or slightly above the surrounding soil grade.
Backfill the hole with the original soil, tamping it lightly to remove any large air pockets. After planting, a thorough, deep watering is required to settle the soil around the root mass and create necessary root-to-soil contact.
Routine Watering and Feeding
Consistent moisture is essential for a newly planted ‘Mr. Bowling Ball’ arborvitae during its first growing season. For the first year, the plant should receive deep watering once or twice a week, especially during high heat or drought, to encourage a deep, extensive root system. Maintain evenly moist soil without allowing it to become waterlogged, which quickly leads to fungal issues like root rot.
Once the shrub is well-established (typically after the first year), its watering needs become significantly lower, as it exhibits moderate drought tolerance. Reduce watering to an as-needed basis, generally when the top two to three inches of soil feel dry to the touch. When watering is necessary, it must be deep and slow, allowing the water to penetrate the entire root zone.
This dwarf cultivar is a light feeder and does not require regular, heavy fertilization, which can promote rapid, weak growth that ruins its compact form. If the shrub shows signs of stunted growth or foliage discoloration, a light application of a balanced, slow-release granular fertilizer may be beneficial. Apply this fertilizer once in early spring, just as new growth begins, spreading it around the drip line and keeping the granules away from the trunk base.
The ‘Bobozam’ cultivar naturally maintains its tight, spherical shape without requiring annual shearing or heavy pruning. Pruning should be limited to the removal of dead, damaged, or diseased branches, which can be done at any time of year. If minor shaping is desired, a light trim can be performed in late winter or early spring before the new growth flush begins.
Preventing Pests and Environmental Stress
While the ‘Mr. Bowling Ball’ arborvitae is generally a resilient plant, monitoring for specific pests is important. Spider mites are a common issue, often signaled by fine webbing on the foliage and a dull, bronzed appearance of the needles. A strong jet of water can dislodge these tiny arachnids, or horticultural oil can be applied for control when infestations are severe.
Another potential concern is the bagworm, a caterpillar that constructs a spindle-shaped silk bag camouflaged with foliage. Manual removal and destruction of the bags before the eggs hatch in late spring is the most effective non-chemical control method. Scale insects are also occasional pests that feed on plant sap, indicated by yellowing foliage or the sticky residue known as “honeydew.”
Environmental stress, particularly winter burn, is a significant threat to all arborvitae, especially in exposed locations. Winter burn is a form of desiccation that occurs when evergreen foliage loses moisture to harsh winter winds and sun, but frozen ground prevents the roots from replacing water. This results in the browning or bronzing of the needles, often on the side facing the prevailing wind and sun.
To prevent this damage, ensure the shrub is deeply watered in late fall before the ground freezes solid, allowing the foliage to enter winter fully hydrated. Applying a layer of organic mulch around the base helps insulate the roots and moderate soil temperature fluctuations. For plants in highly exposed areas, temporary burlap barriers can be erected on the windward side to shield the shrub from drying winds and intense winter sun.