When receiving the Dieffenbachia, do not repot immediately but wait at least 6-12 months or if the roots are beginning to get crowded and growing through the drainage holes.
Repot in the spring, using a 2 inches bigger pot to keep the roots drier. (Too big of a pot could cause the soil to dry slower, which is not helpful.)
Place a piece of screening at the bottom of the container over the drainage hole to secure the soil and allow them to drain. Use a well-draining indoor potting mix with perlite to help with drainage.
Water your plant in the old pot before transferring over and let them sit an hour.
Add soil to the bottom to elevate the root ball. Lift the plant and release the roots against the existing planter. Use a clean knife or garden trowel to wedge between the pot and the soil to loosen.
Inspect the root ball. Notice if there are any dead or rotting roots and trim off with sterile pruners. If the plant is rootbound, cut through the roots to alleviate continued encircling.
Ensure the plant is sitting about 1 inch below the edge of the pot to avoid water spillage. Add more soil and backfill around the sides by tamping down. Fill up to the soil line but not over.
Water thoroughly, leaving the soil damp but not soggy. If settling occurs, add more soil.
Water well to dampen the soil and let it drain.