The Thuja occidentalis, also called American arborvitae, is an evergreen tree that is native to North America. The tree is a slow-growing variety that forms an upright, pyramid shape. Thuja occidentalis is planted in home gardens as a border or hedge, or used as an accent tree in rock and flower gardens.
The Thuja occidentalis is a needled evergreen that grows to a height up to 30 feet and spread of 6 feet. The tree has a columnar form and does not produce fruit or cones. The leaves have a fine texture and a fan-like shape.
Thuja occidentalis is an evergreen that is hardy to plant in USDA growing zones 2 through 7. The tree grows best in a well-draining soil, such as sandy loam or clay loam, but will grow in most soil types. The soil should be acidic, with a pH of 4.5 to 8. Ground rock sulfur can be worked into the soil to reduce the pH number (acidity level). Thuja occidentalis prefers to grow in an area that has full-sun conditions. The foliage will lose density when grown in too much shade.
Thuja occidentalis should be provided with supplemental water when planted in a hot and dry climate. Water the tree once a week with a deep watering that absorbs to a depth of 10 inches when the weekly rainfall amount is less than 1 inch. Mulch can be applied around the root ball of the tree to assist with moisture retention in the soil. The mulch should not be placed within 4 inches of the tree trunk. Apply a high phosphorus fertilizer at the time of planting, and continue to fertilize each spring with a balanced fertilizer to maintain the health of the tree.
The Thuja occidentalis tree is propagated to produce new trees by taking heeled cuttings from side shoots that are at least two years old. The bottom of the stem cutting should include a heel portion that is from older stem tissue. The cutting can be rooted by dipping the cut end into rooting hormone powder, and sticking it into a tray filled with moistened rooting hormone. The stems can be transplanted into individual growing containers once the roots reach 1 inch in length.
Thuja occidentalis trees have few problems with diseases and insects, except for an occasional infestation of bagworms or spider mites. Spider mites cause yellow speckles on the foliage and can be removed by spraying the tree with a sharp stream of water. Follow up by spraying the tree with an insecticidal soap to prevent the mites from returning. Bagworms defoliate the tree branches and form egg sack bags that hang from the tree. Remove the bags and spray the tree with an insecticide when the worms are in the larvae stage. Prevent an insect infestation by spraying the tree in spring with horticultural oil.