Select a site for thuja occidentalis 'Smaragd' where the shrub will be exposed to full sunlight or partial shade. Soil should be well-drained.
Dig a hole at least twice as wide as the shrub's root ball. The depth of the hole should be no deeper than the height of the root ball.
Remove the shrub from the nursery container and set it in the hole. If the root ball is wrapped in burlap, cut the top 1/4 to 1/3 of the burlap off or fold the burlap down around the plant so the burlap won't poke up above the soil. Cut off any strings or wires. Be sure the crown of the shrub, which is where the trunk meets the roots, is 1 to 2 inches above the surface of the soil. If necessary, adjust the soil in the bottom of the hole to bring the shrub to the correct level.
Fill the hole about 2/3 full of soil, then fill the hole with water. Allow the water to drain, then finish filling the hole with soil. Water deeply.
Spread 2 to 3 inches of mulch, such as bark chips, shredded leaves or pine needles, around the tree. Leave a 6-inch span around the trunk uncovered so that mulch won't pile up against the trunk.
Keep the soil evenly moist for the first year. Place a soaker hose at the base of the tree or allow a garden hose to drip. Water the tree in this way for an hour once or twice every week when there is no rainfall. Once the tree is established, water only during extended hot, dry periods.