When receiving the Begonia plant, 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 one inch wider in diameter pot to keep the roots more snug (they like to be root bound). (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 it to drain.
Use a well-draining indoor potting mix with perlite, coconut coir and vermiculite to help with drainage, moisture retension and absorption of nutrients.
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.
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.
Plant outside in a warm plant zone (10-12) or after the last frost in your planting zone (where the temperature is above 60°F) in well-draining soil and keep consistently moist but never soggy. Mix in compost or well-draining garden soil and root hormone to get it established. Plant them about 1 inch in depth and 10-12 inches apart if planting several. Keep in a part sun (early morning) garden where direct light will not burn the leaves.