An arborvitae is an evergreen species that grows as a tall columnar tree or may be pruned to maintain a large shrub size. Arborvitae plants have flat, scale-like foliage with no flower production. The tree grows best in U.S. Department of Agriculture Hardiness Zones 4 through 9 where they prefer a partially shaded area that has well-draining soil. Propagate established arborvitae trees that are at least 3 years old by cutting branch sections from mid-summer to early fall.
Cut a 6-inch semi-hardwood branch piece from the arborvitae tree with a sharp, clean knife. Choose a piece from current year growth that is beginning to mature and turn to a woody texture.
Create a propagation soil by mixing equal amounts of sterile peat moss, perlite and course sand. Prepare the soil in a large bowl. Add water to the mixture until it has the consistency of a moist sponge.
Add the damp soil mixture to a clean propagation tray. Remove all leaves from the lower half of the arborvitae stem and dip the cut point into powdered root enhancing hormone. Stick the lower half of the stem into the propagation tray and firm the soil to hold in place.
Apply a light misting of water to the arborvitae stems and propagation soil. Cover the tray and arborvitae stem with a clear plastic bag and set it in a warm area that receives at least six hours of indirect sunlight.
Open the plastic bag once a day to refresh the air around the arborvitae stem. Apply a light mist of water to the stems and soil mixture and close the bag around the stem.
Check for root development after five weeks of growth by gently pulling on the arborvitae stem. Resistance indicates that there is root growth on the stems. Move the soil gently with your finger to verify the root length.
Transplant the arborvitae stem to a container once the root growth is 1 inch or longer. Fill a 4-inch diameter planting container with a sterile potting mix and transplant the stem to the same depth it was growing in the propagation tray.
Grow the transplanted arborvitae stem indoors for a minimum of one year. Transplant the stem to an outdoor growing space in the spring season to give it time to establish during the summer growing season.