A Few Facts About The Tuberous Begonia
Its scientific name, Begonia tuberhybrida, says a few things about the beautiful tuberous begonia. It grows from a tuber, and its many varieties are hybrids. As is often the case with hybrids, one would expect to see many different varieties, and this is indeed the case. The tuberous begonia flowers come in all shapes, sizes and colors. Some flowers are upright, others are pendulous. Some are single petaled, others, probably most, are double petaled. The male flowers tend to be quite large, up to 6 inches in diameter, and showy. The female flowers are smaller, 1 to 3 inches in diameter, but still showy. About the only common factor among the varieties would be the leaves, which are almost always dark green in color, quite large, and arrow shaped.
Boxes And Containers Are Best - Unlike its cousin, the wax begonia, which is usually considered to be a bedding plant, the tuberous begonia seems best suited for containers and boxes. One reason for this is the size of the male blossoms can make the plant top heavy, and staking the stems is often required, easily accomplished in a window box, but more difficult in a flower bed. This problem usually does not occur with the female blossoms, as they are normally small enough so that they don't add significant weight to the stems.
The upright begonias are at their best in boxes and containers, while other begonias have a flowing or trailing characteristic that makes them ideal for hanging baskets. In buying tuberous begonia tubers it's not only a good idea to know the flower type and color, but also whether the plant is going to be upright or trailing.
Look For The Sprouts - When purchasing tubers, look for ones showing tiny sprouts on their upper (concave) surface. If tubers are planted which do not have sprouts, they usually will not grow. Also, tubers which are planted too deeply will tend to rot, rather than produce plants. A half inch of fine soil is about the maximum cover one should provide for a tuber. Tubers are best started indoors, or in a greenhouse environment. Normal practice is to water the tubers once, and then wait until sprouts appear above the surface before watering again. It can take anywhere from one to six weeks before the sprouts break the surface of the soil. Watering in the interim may drown the tubers, as the roots take time to form and regular watering is not yet needed.
Once the sprouts start to shoot up though it's time to begin watering them regularly. Most gardeners let the soil dry out on the surface before watering. At this stage the begonias like a warm bright location. Indirect sun or partial shade is best. Mature begonias can best handle deeper shade but the young plants need a good amount of light. Just avoid direct hot sun. The plants are ready to be transplanted when the stems are 6 inches tall. Don't stick them out of doors until the danger of frost has passed. The tuberous begonia is not at all frost hardy. It is wise to harden the plants over a period of several days before placing them out of doors permanently.
From Light To Shade - The begonia's permanent location should be one where there is either partial or full shade. While bright light was important to get the plants started, the mature plants like it shady. If planted in window boxes, they will do best on the side of a house or structure that does not get direct sun, at least during mid day. In watering the tuberous begonia, especially one in a container or box, one needs to strike a careful balance between not letting the plant dry out, and over watering it. The soil needs to stay moist, but too much water will cause the tuber to rot. When watering begonias, water at the base of the plant to avoid getting water on the leaves. The tuberous begonia is quite susceptible to fungus on its leaves, and a fungicide will need to be applied at the first sign that this may be happening.
By and large though, the tuberous begonia is a low maintenance plant. If one takes time to dead head the plant when the blossoms are spent, and remove any leaves that may have become wilted, the plant will set new blooms, and should bloom throughout the summer months.
In most places, the tubers should be dug up in the fall if you want to use them again the following year. Unless the soil stays warm and dry during the winter months, the tubers will not survive from one season to the next.