Rex begonias (Begonia rex-cultorum) are distinctive, showy plants with colorful, variegated foliage. Traditionally grown as houseplants, they have enjoyed a resurgence in popularity and are now being grown outdoors, according to Rick Schoellhorn, a horticulturist with the University of Florida. These perennials, which can be somewhat tricky to care for properly, are valued for their large, showy leaves and thrive in warm, humid conditions.
Rex begonias have visually stunning leaves that can be as large as 18 inches in diameter. The flowers, which bloom in the spring, are small and are much less noticeable. The leaves are often patterned in splotches, bands, or spots. They can be bi-colored, one bright but solid color or different shades of the same color, ranging from yellow to pink, orange, purple, cream, green and shades in between. The leaves can be bumpy or smooth and ruffled or heart-shaped, among a variety of other shapes.
Rex begonias have a reputation for being difficult to grow, according to Schultz Nelson, a horticulturist from the University of Illinois, but Nelson suggests that this is because most home gardeners do not understand the importance of providing a humid environment for this plant. Rex begonias need high humidity in order to thrive. Place potted begonias on a tray filled with pebbles and water, or run a humidifier near the plant. While they enjoy humid air, rex begonias do not like overly wet soil. These plants should only be watered when the top layer of soil (down to an inch or so) dries out.
Proper lighting is very important to maintain the bright colors of the rex begonia's leaves. Too much sunlight will bleach the colors out of the leaves, while too little sunlight will cause the colors not to develop properly. Bright but indirect light is best. Outdoor begonias can benefit from a location that offers morning sunlight followed by afternoon shade, while indoor rex begonias should be placed near a window where any direct sunlight is filtered by a sheer curtain or blinds.
Rex begonias can be found where the soil is light and loamy. They do not do well in heavy, clay soils that retain water. Indoor begonias thrive in potting mediums that have a high level of peat moss and sand to aid in drainage.
Rex begonias can suffer from leaf spot, which is caused by a number of different fungi. Leaf spot occurs when water sits on the leaves of the plant, causing them to develop unsightly spots of fungal growth. These spots can spread, causing the leaves to turn brown, shrivel up or rot. Avoid leaf spot by watering your rex begonia carefully so that water does not sit on the leaves. Water in the morning so that the rising sun can quickly evaporate any water that remains on the foliage.