Select a sunny, well-drained location in your yard with plenty of space surrounding it; fully mature "Green Giant" arborvitae grow 20 to 30 feet wide. Dig a hole 3 feet deep and 3 feet wide. Consider adding a mixture of 1/2 humus to 1/2 soil four inches deep in the bottom of the hole, particularly in areas with poor soil quality.
Place the "Green Giant" arborvitae in the hole, covering the tree's root structure with soil and pressing dirt firmly around the tree's stem and roots. Place three bamboo stakes around your newly planted tree. Attach the tree to the stakes with twine. Apply approximately a cup each of root stimulator and the 15-9-12 slow-release fertilizer uniformly around the tree. Water well. Place weed barrier ground cover and mulch at the base of the tree. To achieve a screening effect, plant multiple "Green Giant" arborvitae in a row, 15 feet apart from one another.
Apply an inch of water to your "Green Giant" arborvitae twice a week until well established between one-and-a-half and two months after planting. Keep the soil moist but not wet. Fertilize in late winter and midsummer with 16-4-8 granular fertilizer.