The U.S. National Arboretum was the first to introduce the Green Giant Thuja tree to the world. In 1998, the tree won the prestigious Pennsylvania Horticultural Society Gold Medal Plant Award. The Green Giant Thuja tree is an extremely fast-growing evergreen sentinel tree that is popular in hedge plantings. The tree will grow 5 feet per year until it reaches 60 feet in height with a spread of up to 30 feet. The tree grows in a lovely pyramidal to conical shape with no pruning. It can be grown in a wide range of soil from sandy loam to heavy clay.
Plant the Green Giant Thuja six weeks before the last frost of the season. This early planting allows the tree to easily adjust to its new climate. In mild climates the tree can be planted in the wintertime if the ground is not frozen.
Keep the roots of the Green Giant Thuja moist until planting can occur. The trees can easily suffer root damage if the roots are allowed to dry out before planting can occur. Mist the tree roots with a hose or set the plants in a large bucket of water.
Dig a hole that is twice as large at the root system of the Green Giant Thuja that you will be planting. Place the tree into the hole and gently spread the roots out. Be careful not to bend or break any of the roots. Fill the hole in with the garden soil. Tamp the soil down firmly to make sure there are no air pockets. Water the tree thoroughly once planted. Apply 3 to 4 inches of mulch around the base of the tree to help keep the roots moist. Use peat moss, bark chips, sawdust or recycled plastic mulch. Mulch will also help keep weeds away from the base of the tree. Keep a 2-foot weed and grass free zone around the base of the tree so there is no competition for nutrients.
Water the tree regularly. Keep the tree moist, especially in times of drought. The Green Giant Thuja does not care to have waterlogged roots but it does like the soil to stay moist around its root system.
Fertilize the Green Giant Thuja tree once a month in the spring, twice a month during the summer and cease fertilizing in the fall. Fertilize using a 10-10-10 or 20-20-20 fertilizer. Follow the directions on the label for fertilizer application. Water the fertilizer thoroughly once applied.