Add a few inches of potting mix to the bottom of a container with drainage holes. Use soil blend rich in organic matter and with peat moss for good drainage. Spring is the best time to repot dieffenbachia.
Ease the plant out of its old pot, wearing gloves to prevent your skin from coming in contact with the plant’s sap. Examine the roots and trim any that are broken, discolored or mushy.
Place the plant in the new pot. Add or remove soil until the root crown is at the same height as it sat in the old container. Leave 1/4 inch of space between the pot’s rim and the plant’s base to keep water from overflowing during irrigation.
Water the repotted plant until excess drips out of the drainage holes. Add more soil to the planter if settling occurs. Irrigate the dieffenbachia every time you put more potting mix in the container.