Thuja (Arborvitae) are popular evergreen conifers highly favored for creating dense, year-round privacy screens and hedges. The genus is widely utilized in landscaping due to its hardiness and versatility. A primary concern for homeowners selecting this plant is its growth rate, which dictates how quickly a desired height or screen density will be achieved. The actual speed a Thuja gains height depends heavily on the specific cultivar chosen and the environmental conditions provided.
Growth Rate Variability by Thuja Cultivar
The inherent growth potential of a Thuja is genetically determined, leading to a wide spectrum of annual growth rates across different varieties. These rates generally categorize cultivars into fast, moderate, and slow growers, which directly influences their suitability for specific landscaping needs.
The fastest-growing option is the ‘Green Giant’ (Thuja standishii x plicata), a hybrid known for its impressive performance. Once established, this cultivar can easily add between three and five feet of height per year under optimal conditions. This rapid vertical growth allows it to quickly reach its mature height, which can range from 30 to over 50 feet.
In contrast, the widely planted ‘Smaragd’ (Emerald Green Arborvitae, Thuja occidentalis ‘Smaragd’) exhibits a much slower rate. This selection typically grows at a moderate pace, gaining only six to twelve inches annually. Its slow growth is valued for its ability to maintain a tight, narrow, pyramidal shape with minimal pruning, ultimately reaching a manageable mature height of 12 to 15 feet.
The native American Arborvitae (Thuja occidentalis) generally falls into the moderate growth category, averaging between one and two feet of new growth each season. Western Red Cedar (Thuja plicata) varieties, such as ‘Spring Grove’, show a medium-to-fast rate, often adding two to three feet per year.
Environmental Conditions That Impact Growth Speed
While the cultivar dictates the maximum potential growth rate, external environmental factors determine how closely the plant meets that potential. Light exposure is a major influence, with plants in full sun—receiving at least six hours of direct light daily—developing denser foliage and achieving faster growth than those in partial shade.
Soil quality and drainage are also significant determinants of growth speed. Thuja requires moist, well-drained soil. Planting in heavy clay can severely restrict growth because clay soil compacts easily and reduces oxygen availability to the roots. Poor drainage often leads to root rot and stunted development, while well-drained loamy soil promotes the healthy root system necessary for rapid vertical growth.
Climate zone and temperature stress further modify a plant’s annual performance. While Thuja is generally cold-hardy, prolonged exposure to harsh winter conditions can slow growth. Winter desiccation, or “winter burn,” occurs when the evergreen foliage loses moisture to dry, cold winds faster than the roots can absorb it from frozen ground. This damages the tips and reduces the following year’s growth capacity.
Water availability is a limiting factor, particularly during the growing season. Drought stress forces the plant to conserve resources, which directly results in diminished height gain. Consistent moisture throughout the root zone is necessary to support the high metabolic rate required for rapid growth.
Practical Care Strategies for Maximizing Height
To ensure a Thuja achieves its inherent genetic growth rate, proper planting technique and consistent intervention are necessary. When planting, the hole should be dug two to three times wider than the root ball, but not deeper. This ensures the top of the root ball sits level with or slightly above the surrounding soil line to prevent waterlogging.
Immediate and consistent watering is necessary for newly planted Thuja to encourage root establishment. During the first two to three months, the plant requires deep watering several times a week. After establishment, the goal is to provide about one inch of water per week. This approach encourages roots to grow deep rather than remaining near the surface.
Strategic use of fertilizer can optimize growth, especially in nutrient-poor soils. Applying a slow-release, balanced fertilizer, such as a 10-10-10 or a high-nitrogen evergreen formula, in early spring encourages the flush of new growth. Avoid late-summer fertilization, as this can stimulate soft, vulnerable growth that will not harden off before winter.
Pruning should be minimal if the goal is maximum height, focusing only on light trimming to encourage density. Removing small amounts of growth from the sides stimulates the plant to fill out, creating a denser privacy screen. Avoid “topping” the tree, which removes the central leader; this practice permanently halts vertical growth and compromises the plant’s natural pyramidal shape.