Rex begonias (Begonia Rex-cultorum group) come in a wide range of colors, textures and shapes. The rex begonia originated in the forests of northern India, and now more than 1,300 species and countless cultivars are grown all over the world. In North America, the rex begonia is most often grown as a houseplant or in the garden as an annual. In tropical and semitropical climates, the plant is considered a perennial.
Rex begonias are a type of rhizomatous begonia. They are grown for showy leaves with streaks of color, such as pink, purple, yellow, white and chocolate with silver spirals. The flowers are secondary to the bold colors of the leaves. The leaves also come in an extensive variety of shapes, such as spirals, making them popular with collectors.
Bright, but indirect sunlight is best for the rex begonia. Variegated plant leaves usually require more light than plants with plain green leaves. Hot direct sunlight has been known to bleach out the brilliant colors. Ideal temperatures should always be above 60 and around 70 degrees Fahrenheit during the day.
Humidity is important for the rex begonia. More than 50 percent relative humidity is required and this can be difficult to achieve indoors during the winter. Humidity can be increased by keeping the plant in a tray filled with water and pebbles. However, the rex begonia does not like wet feet so water should never touch the bottom of the plant. Another option is to run a humidifier.
Rex begonias are slow growers. It can take up to six months to produce a new plant. The most common form of propagation is leaf cutting as the leaves are most readily available. Seeds can also take about six months. Stems can be harvested for cutting, and in ideal conditions, can take root in about 20 days.
Over-watering will kill the rex begonia. Good drainage is necessary and water should never be allowed to sit in the pot. Even though the Rex begonia thrives with humidity, it will not thrive with wet conditions. Instead, it will succumb to fungal diseases such as botrytis and mildew. Additionally, highly concentrated fertilizer will burn the rex begonia.
Watering according to the calendar should be avoided. The rex begonia should be watered when the top of the soil just begins to dry out and the begonia should not be allowed to wilt. Organic soluble fertilizer works best, but the rex begonia will not grow, or use fertilizer efficiently if the temperature is below 58 degrees F.