Rex begonias are a colourful addition to your indoor or patio potted plants. Grown for their foliage, the leaves come in shades of green, red, pink and silver. Rex begonias grow from a rhizome, which is a root system that sprouts buds and roots to grow into the plant. The rhizome is cut apart and divided in order to propagate new plants. Divide a Rex begonia when it begins to outgrow its pot or once the plant is at least three years old if you want to add more begonias to your houseplant collection.
Lift the Rex begonia tuber from the pot with a spade or your hands. Avoid nicking or cutting the tuber if you are using a spade.
Brush off the excess soil and inspect the rhizome to find the buds. These resemble pink or red bumps, similar to the growing eyes on potatoes.
Cut apart the tuber with a sharp knife, leaving three growing eyes on each piece. Cut away any shrivelled or soft and rotten sections of the tuber and discard these.
Brush fungicide onto each cut surface of the roots to prevent disease. Begonia fungicide is available at garden centres.
Fill an 8-inch diameter pot with well-draining soil mix. Water until it begins dripping from the bottom drainage holes to ensure it is moist throughout.
Plant a tuber section per pot. Plant with the flat or concave section of the root facing up. Sow so the surface of the tuber is right at or right beneath soil level.
Place in a brightly lit, 60 to 70 degree F room and keep the soil moist but not soggy. Fertilise every two weeks with a liquid houseplant fertiliser.
Divide rex begonia in early spring right before the plant begins growing again. This is usually in March. Plants are root bound when you can't insert a pencil into a drainage holes on the pot.
Begonia roots are prone to rot immediately after dividing. Letting the cut sides dry overnight before replanting as well as the use of fungicide helps prevent this.