Small: 4 inch standard nursery pot.
Medium: 6 inch standard nursery pot.
Light
Rex begonias like bright, indirect light year-round. Because they are not aggressive bloomers, they can tolerate less light than other begonias and will thrive under fluorescent lights.
Water
Rex begonias require regular water, but be careful not to over-water them. They also thrive on humidity but don’t like direct misting, which encourages powdery mildew. Let the soil surface become dry to the touch before watering.
Plant Specific Care
Temperature and HumidityRex begonias do best in moderate temperatures (60 to 70 degrees Fahrenheit) and moderately high humidity (around 50 percent). They cannot tolerate freezing, and some types of rex begonias go into a dormant period during the fall. As with other begonias, the rex and other foliage begonias prefer the same humid, gentle environment in which understory ferns thrive.FertilizerUse liquid fertilizer weekly at quarter strength or at half strength every two weeks.Potting and RepottingRex begonias are rhizomatous plants that grow from a shallow and knobby rhizome. As such, they do best in large, relatively shallow pots where the rhizome has room to spread. If the rhizome still has room to grow in its pot, the begonia should be considered happily potted. When the rhizome begins to butt up against the sides of the pot, however, it’s time to repot into a fresh pot with fresh soil. Divide the rhizome when repotting to increase your plant stock. As with all begonias, don’t soak the soil of newly potted plants, but do keep it lightly moist and warm.Propagating Rex BegoniaThe vast majority of begonias offered in the trade are hybrids and thus cannot be accurately propagated from seed. Rhizomatous begonias such as the rex begonia can be easily propagated by rhizome division during repotting. Almost all begonia species will readily sprout from leaf-tip cuttings. A rooting hormone can help the cuttings sprout.
Rex begonias can also be propagated by pinning a leaf to the bedding mix and making small incisions in the leaf veins or by inserting a leaf (with a petiole) directly into the soil. The petiole is the stalk that attaches the leaf blade to the plant stem. fuller-looking plant.