Rex begonias are favored for their colorful leaves in a variety of shapes, with blooms in bright pink, white, purple and yellow, in solid colors, swirl patterns or stripes. Begonias can be slightly fussy, but their primary requirement is plenty of humidity. Rex begonias are easy to propagate by a split vein leaf cutting.
Fill a pot with a mixture of three parts sand and one part peat moss. Any container with good bottom drainage will work, but the container must be wide enough to accommodate a Rex begonia leaf laid flat on the soil.
Set the container in a saucer of water. Allow the container to sit in the water until the potting mixture is slightly damp all the way through.
Remove a leaf from a healthy Rex begonia plant. Using a sharp knife or new razor blade, make several cuts through the leaf's major veins.
Lay the leaf on the potting mixture with the underside of the leaf flat against the soil. Make sure the leaf makes full contact with the soil. If necessary, use bent paperclips to hold the leaf firmly in place. New plants will form at each cut area.
Slide the container into a plastic bag. Place the container where the leaf will be exposed to bright but indirect light.
Check the potting soil regularly. If the soil feels dry to the touch, it must be misted immediately. Use distilled water, which will be sterile and free of minerals that can damage the leaf.
Watch for the leaf to develop tiny plantlets at each cut. Allow the plantlets to grow to about 2 inches tall, and then plant each new plantlet in its own container filled with commercial potting mixture. At this point, the young plant should be treated as an adult Rex begonial.