The thuja green giant is a pyramid-shaped coniferous tree that has evergreen, scale-like foliage. In comparison to other thuja tree species, the green giant grows taller, usually attaining heights of between 30 and 50 feet. However, older thuja green giants can grow to 60 feet and above. Landscapers commonly use the trees in hedges and groupings or to form privacy screens. You can expect a thuja green giant to survive for at least 40 years, provided it grows in the proper conditions.
Background
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Scientists classify thuja green giants as arborvitae, as the trees are derived from Eastern Asian and European conifers in the cypress family. However, the thuja green giant is not a naturally occurring tree, but a man-made hybrid. Horticulturists created the tree by cross-pollinating a western red cedar (Thuja plicata) with a Japanese thuja (Thuja standishii). The thuja green giant first appeared in the U.S. in 1967 and is known for its cinnamon-colored bark, uniform shape and resistance to disease, pests and drought. The tree can tolerate many soil types, ranging from heavy clays to sandy loams.
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Variables
Predicting how long a thuja green giant will be able to survive is difficult, as there are many variables that can impact longevity. For example, the United States Department of Agriculture, or USDA, recommends that you grow thuja green giant trees in hardiness zones 5 through 7. If you try to grow the trees outside of these zones, the trees will likely suffer from poor development -- if they develop at all -- and die prematurely. Specific environmental circumstances can also impact longevity. For example, if you grow a thuja green giant in a large, fertile field, where it has plenty of room to spread its roots, it will likely live longer than a thuja green giant growing in a small, urban lot, where its growth is inhibited by concrete. Other variables that can impact the tree's lifespan include overcrowding and exposure to lawn chemicals.
Estimate
According to the University of Washington, most arborvitae trees live between 40 and 150 years. So you can safely assume that a well-cared for thuja green giant, grown in the proper USDA hardiness zone, will live for at least four decades.
Exceptions
In ideal circumstances, a thuja green giant could live for considerably longer than the 40 to 150 year range. According to the University of Washington, while scientists know that some arborvitae trees can live for over 200 years, recent evidence suggests that arborvitaes may be able to live for over 1,000 years.
Age Indicators
Apart from growing taller and wider, a thuja green giant shows its age through changes in its bark. Older trees have bark that is thicker and more fibrous. Of course, the most accurate way to tell the age of a thuja green giant is to count its trunk rings once it falls or needs to be cut down.