Reliable plants used for hedges, barriers and windscreens, arborvitae (thuja spp.). Generally, arborvitae is not an exceptionally fast-growing shrub, and insufficient watering slows it down even more. Standishii) is an exception, being one of the faster-growing arborvitaes, but its growth is much more than most home gardeners are looking for. Green giant shrubs can climb to a towering height of 50 to 60 feet at maturity, with a spread of 12 to 20 feet. Mature size the american arborvitae grows to a height of 4060 and a spread of 1015 at maturity. Growth rate this tree grows at a slow to medium rate, with height increases of anywhere from less than 12 to 24 per year. Dark american arborvitae-an excellent medium height option for a privacy screen. Well suited for areas where height is needed but mature width is an issue. soft, fragrant evergreen thats tough and timeless why thuja techny trees? Known for its robust strength and good looks to match, the thuja techny tree is second to none. Compared to similar arborvitaes, the thuja techny stands up extremely well to temperature extremes, drought, and air pollution. And its adaptable to any soil type, as well as resistant to pests and diseases.