- 1). Place your rex begonia plants in an area of your house or garden that provides partial shade at approximately 1,500 to 2,500 footcandles. Grow these plants indoors near a curtained window for filtered, bright, indirect light. Avoid direct light, which will bleach leaves.
- 2). Irrigate your rex begonias as necessary through methods that water the soil directly; overhead irrigation can result in bacterial disease. Touch the top layer of soil with your finger and only water once the soil feels dry. Maintain extremely well-drained, moist soil that's high in organic content with a pH of 5.8 to 6.8.
- 3). Create the humid environment rex begonias prefer if your outdoor space is not humid. Maintain a relative humidity above 50 percent, when possible. Place rex begonias on water-filled trays for added humidity.
- 4). Maintain daytime temperatures of 70 to 80 degrees Fahrenheit and nighttime temperatures of 65 to 70 degrees Fahrenheit for best growth.
- 5). Fertilize rex begonias with a slow-release, balanced fertilizer during the growing season for good foliage growth.
- 6). Add a 2- to 3-inch layer of organic mulch like wood chips or pine needles to the area of soil surrounding your in-ground rex begonias to keep the soil warm, retain moisture and prevent weeds from developing. Do not press the mulch directly against the stems.
Source...