Transplanting the houseplant dumb cane, also known as dieffenbachia, is relatively simple and can be completed in five steps. Dumb cane plants grow too large for their pots every two or three years, depending on the size of the pot. When this happens it's necessary to repot or transplant into a larger container to provide room for the roots to grow.
Pour water in the soil to determine whether your dumb cane's roots have outgrown their container. If the water immediately flows out through the drain hole in the base, your dumb cane is pot bound and it's time to transplant. Assemble your supplies, including a new container that is 3 inches in diameter larger than the current container. If you select a container that is too large, plant growth will be slow while the roots attempt to fill the container.
Wash the new container for the transplanted dumb cane. If the container is unglazed pottery, soak it for two hours. Put newspapers on your work surface to make cleanup easier. Place small pebbles or clean broken pottery over the hole to improve water drainage. Cover the base of the pot and pebbles with 1 to 2 inches of houseplant potting soil, or about 10 percent of the depth of your pot.
Hold the dumb cane upright and scrape the inside edges of the plant's pot with a long sharp knife to loosen the soil and rootball from the walls of the container. Do this when the soil is dry. Slowly lift the plant and rootball out of the container.
Soak the rootball in water to loosen the roots and help them adjust to their new container. Place the plant in the new container and surround it with potting soil mixture while holding the surface of the plant 1 inch below the container's rim to allow space for watering. Once the potting soil is in place, gently pack it down with your fingers until it's firm to stabilize the transplanted dumb cane. Add more soil if necessary to keep the plant slightly below the container's rim.
Place your container and dumb cane in a sink and soak the soil with a gentle spray until water runs out through the drain hole. When the draining water stops, return the plant to its former location. Ideally this has bright light but not direct sunlight. Place a shallow drain dish under the container to capture any remaining water and protect the surface on which the container rests. Cover the dumb cane with a large, loose and clear plastic bag for two or three days. Do not restrict air circulation around the plant by sealing the bag. The bag increases the humidity around the plant and minimizes transplanting shock. Remove the bag and resume the plant's previous watering schedule.