The different cultivars within the begonia family provide a gardener with many begonia choices for both indoor and outdoor growing. Rex begonias are members of the rhizomatous begonia subsection, with these begonias putting forth plentiful and colorful foliage when growing conditions are correct. Gardeners living in USDA zones 10 and 11 can grow rex begonias outdoors and all other gardeners must grow these showy plants indoors. Give rex begonias ample humidity and indirect sunlight and they will thrive for years.
Place the rex begonia in a growing location that receives indirect sunlight with temperatures of about 70 degrees F. Placing the container three to four feet back from an eastern or western window will provide suitable sunlight.
Fill the shallow dish with gravel and add water to just below the top of the gravel. Place the dish beneath the plant container to add humidity to the area around the plant. Replenish the water level to keep it at the same point beneath the gravel as the water evaporates.
Allow the potting soil to dry slightly between watering. Insert a finger into the soil, and if the soil feels dry 1 inch below the surface, water to moisten the soil.
Fertilize the begonia once or twice per month by mixing fertilizer with water following package recommendations for fertilizer mixing strength. Pour the fertilizer over the soil without splashing it onto the foliage to avoid burning the leaves.
Remove old or withered foliage by clipping it off with the pruning shears at the point where the leaf stems connect with the larger stems. Cut back stems or leaves to shape the begonia if it grows too large.