The ‘Thin Man’ Arborvitae (Thuja occidentalis ‘Thin Man’) is a popular cultivar valued for its extremely narrow, columnar growth habit. This evergreen offers a slender, upright form perfect for vertical accent planting or creating dense privacy screens where a wider shrub would be unsuitable. Its ability to maintain a vibrant dark green color throughout the year makes it a favored choice for four-season interest. The plant’s fast-growing nature, reaching up to 15 feet in height while staying only 3 to 5 feet wide, provides quick screening without consuming excessive lateral space.
Site Selection and Soil Requirements
For the ‘Thin Man’ Arborvitae to thrive and maintain its desirable dense foliage, it requires proper sun exposure. It grows best when positioned in full sun, meaning it receives at least six hours of direct sunlight each day. While it can tolerate some partial shade, too little light can cause the foliage to thin out and the rich green color to become dull.
The correct soil composition is important for the long-term health of this plant. Arborvitae prefers moderately moist, fertile soil that drains well. It is sensitive to perpetually wet conditions, which can lead to root rot in poorly drained areas.
The soil’s pH level should ideally be slightly acidic to neutral, though this cultivar is adaptable. Ensuring that water moves through the soil easily is more important than adjusting the pH, as this prevents the roots from becoming waterlogged. Amending heavy clay soil with organic material can help improve fertility and internal drainage.
Planting Techniques and Initial Establishment
When preparing to plant, the hole should be dug significantly wider than the root ball, typically two to three times the width. The depth of the hole must not be deeper than the root ball itself. This prevents the plant from settling too low, which can compact the soil and impede oxygen exchange to the roots.
The root flare, the point where the trunk begins to widen, must be positioned at or slightly above the surrounding soil line. Planting too deep is a common mistake that can lead to trunk rot and plant failure. Backfill the hole with native soil, avoiding excessive amendments that can discourage roots from growing into the surrounding landscape.
After backfilling, the new plant needs a thorough, deep watering to settle the soil and eliminate air pockets. Applying a two-inch layer of organic mulch around the base helps conserve moisture and regulate temperature. Keep the mulch pulled back a few inches from the trunk to prevent moisture buildup against the bark, which can cause rot.
Routine Hydration and Seasonal Protection
Once established, deep, infrequent watering is more beneficial than light, frequent sprinkling. This encourages a deeper, more resilient root system that can withstand drought. Monitor soil moisture, especially during dry spells and for the first two years, by checking a few inches below the surface to ensure it is not completely drying out.
Fertilization is generally light for this cultivar, as heavy feeding is not required. If the foliage appears sparse or growth is slow, apply a balanced, slow-release granular fertilizer in early spring before new growth begins. Always follow product instructions to avoid over-fertilizing, which can cause chemical burn.
Seasonal protection guards against “winter burn,” which is desiccation caused by frozen ground preventing water uptake while sun and wind dry out the foliage. A deep watering just before the ground freezes in late fall is the most effective preventative measure. Heavy snow or ice can cause the narrow branches to splay open, so gently brushing off the excess accumulation can prevent structural damage.
Pruning for Shape and Managing Common Pests
The ‘Thin Man’ cultivar maintains its narrow, columnar shape naturally and typically requires minimal pruning. Any necessary shaping should be done with light shearing in late spring or early summer, trimming only the soft new growth. This gentle trimming encourages the plant to become denser and more compact.
A crucial rule for all Arborvitae is to never cut back into old wood where no green foliage remains. The plant does not reliably regenerate from bare, woody stems, and severe cuts leave permanent, unsightly brown voids. If a branch is damaged or dead, remove it completely back to the main trunk or to a point of healthy, green growth.
Two common pest threats are spider mites and bagworms. Spider mites thrive in hot, dry conditions and cause foliage to turn a dull, bronzed color. They can be managed with a strong jet of water to dislodge them, though specialized miticides may be necessary for heavy infestations. Bagworms create silken bags and feed on the needles, causing significant defoliation. These pests should be physically removed by hand and destroyed before the eggs hatch in late spring.