Arborvitae, belonging to the genus \(Thuja\), are popular evergreen conifers widely chosen for creating dense privacy hedges and landscape screening. The common name, Latin for “tree of life,” suggests their hardiness. People often seek to understand the annual growth rate of these plants to quickly establish a visual barrier. This rate is highly variable, determined by the specific genetic makeup of the plant. Understanding the inherent speed of the chosen cultivar is the first step in setting realistic expectations.
Understanding Growth Rates by Cultivar
The rate at which an Arborvitae gains height each year is primarily dictated by its genetics, which categorize popular varieties into distinct speed groups. The fastest-growing options are typically hybrids, such as the ‘Green Giant’ (\(Thuja\) \(plicata\) \(\times\) \(standishii\)), a cross between Western Red Cedar and Japanese Arborvitae. Under favorable conditions, the ‘Green Giant’ routinely adds three to five feet of vertical growth annually once its root system is established. This rapid growth makes it the preferred selection for homeowners seeking a tall, complete privacy screen quickly.
In the medium-speed category, cultivars like the ‘Techny’ (\(Thuja\) \(occidentalis\) ‘Techny’) offer a moderate, but substantial, growth rate. The ‘Techny’ gains approximately one to two feet in height each year. This moderate pace provides respectable height gain while maintaining a dense, robust form that holds up well in cold climates.
Conversely, the ‘Emerald Green’ (\(Thuja\) \(occidentalis\) ‘Smaragd’) is classified as a slow-growing cultivar, making it ideal for smaller spaces where controlled height is desired. This variety typically exhibits an annual increase of only six to twelve inches. While this speed requires more patience, it results in a naturally narrow, compact, and low-maintenance column.
Environmental Conditions That Impact Growth
A plant’s genetic potential can only be reached if the surrounding environment provides ideal support, meaning external factors significantly modulate the actual yearly growth. Arborvitae require a minimum of six hours of direct sunlight daily to properly fuel the photosynthesis necessary for rapid vertical extension. Trees planted in areas with lower light levels will exhibit sparse foliage and a reduced growth rate, as the plant prioritizes energy to the outer, sun-exposed branches.
Soil quality and moisture management are equally important factors. Arborvitae prefer well-drained, moist, loamy soils and are intolerant of standing water, which can lead to root rot. Conversely, long periods of drought induce severe water stress, which can dramatically stunt development; studies have shown that high water stress can reduce the annual growth of \(Thuja\) \(occidentalis\) by up to 80%. Heavy clay soil can also impede growth by preventing water from draining effectively. Furthermore, the plant’s long-term health is tied to its local hardiness zone, as extreme cold or heat can cause stress that diverts energy away from new growth.
Actionable Steps for Optimal Growth
Homeowners can take specific, routine maintenance steps to ensure their Arborvitae maximize their annual growth potential. Proper watering is a foundational requirement, especially during the first two to three years of establishment. The goal is to provide deep, consistent moisture, typically about one inch of water per week, encouraging the roots to grow deep. This deep watering is far more effective than frequent, light sprinkling, which only wets the soil surface.
Fertilization should be applied strategically to support the energy demands of rapid growth. A slow-release granular fertilizer with a balanced ratio, such as 10-10-10 or 14-14-14, works well when applied in the early spring before the main growth flush begins. Nitrogen-rich formulas, such as 19-6-12, can also be used to push vertical growth. Fertilization should be avoided entirely during the first year or during periods of extreme heat or drought to prevent root burn and unnecessary stress.
A two- to three-inch layer of organic mulch spread over the root zone helps conserve soil moisture and regulate temperature, which are favorable to uninterrupted growth. Light pruning, often called “tipping,” involves trimming the new, soft growth at the ends of the branches in early spring. This technique promotes lateral branching and density without sacrificing vertical height. Avoid cutting back into the old, brown wood that will not regenerate foliage.