A containerized tree seedling unit including an elongated container around the roots of a tree seedling and made of a claylike mud in and around the roots, and means for maintaining the container in a semi-rigid state for handling, storing and planting purposes. Peat moss and/or fertilizer may be included in the mud. A method of producing this containerized unit which includes pressing a body of moist clay-like material into and around the root system of the seedling to form the container.