Thuja Green Giant arborvitae (standishii x plicata) has replaced Leyland cypress as the landscaper's plant of choice for an evergreen hedge or specimen tree. It received the Pennsylvania Horticultural Society Gold Medal Plant Award in 1988 and remains popular because of its fast growth and low-maintenance. Young plants grow 3 to 4 feet per year. Their roots are fairly shallow, but strong enough to prevent the tree from toppling in high winds.
The root systems of arborvitae are generally shallow depending on the variety and may spread to the dripline or edges of the branches, according to North Dakota State University. Green Giant Arborvitae are not known for having invasive or aggressive roots.
For transplanting, dig the root ball to a depth of at least two-thirds of the spread of the branches, according to nurseryman Mike Hirst. Or dig a root ball at least 12 inches deep for every 1 inch of the diameter of the trunk. The major roots of a large arborvitae reach 18 to 24 inches deep, while the roots of smaller trees reach to 8 inches deep.
Good growing conditions, such as adequate watering and fertilizer will help young plants develop strong, deep roots. Green Giant Arborvitae thrive in most soil types between USDA plant hardiness zones 5 to 7. They prefer somewhat moist conditions and full sun. Like all arborvitae, Green Giant arborvitaes may suffer winter damage in very cold climates. Water them at least monthly in cold, dry climates and wrap trees in burlap in exposed areas.
The Green Giant arborvitae is suitable for planting as a single specimen, as a hedge or to hide or screen an unsightly view. Its shallow roots won't damage foundations or septic systems. However, it reaches 60 feet high, so plant it away from buildings where it has plenty of room to grow. Pruning it to control size is not recommended, advises the University of Arkansas Division of Agriculture.
D.T. Poulsen, of Kvistgaard, Denmark, presented a single specimen of Green Giant arborvitae (Thuja) to the United States National Arboreteum. The tree quickly gained attention for its rapid growth and resistance to disease and pests. Wayside Gardens began selling it in the late 1990s and it quickly became a best seller, according to the University of Arkansas Division of Agriculture. The plant is widely available and remains a popular tree for screening or privacy hedges.