Dig a hole outside that's big enough to hold your topiary and the plant that covers it. You can check the plastic label that comes with the plant to see how deep and wide the hole should be. Use a tape measure if needed.
Remove the plant covering the topiary from its pot. Do not rip any of the root structure in the removal process, and leave as much soil as possible around the plant's roots.
Place the planted topiary in the hole and cover with a mixture of moss and potting soil until the plant is stable and the roots are covered completely.
Water your topiary at least three times a day for the first couple of days. This will help the roots get established. After five days, water your topiary once daily. According to Cornell University, topiaries dry out easily and often die because they're not getting enough water.