Bellagio and Mandalay are not tuberous begonias as we know them. True tuberous Begonias (Begonia x tuberhybrida) are either from seed or tubers, difficult from cuttings, and prefer cool moist conditions which limits their sales regions and time of sale across the United States. Tuberous Begonias have minimal heat tolerance and are prone to a variety of root rots that make them somewhat touchy for the average consumer.
They will form a tuber when the daylength is short, the temperatures are cool and the overall light level begins to drop. But even though they form a tuber, they are still way more flexible and summer performing than true tuberous begonias.
These plants need long days, which is why they do so well through the summer; however, this also poses a bit of a problem for early-season production. Remember the conditions they set tubers under (short days, cool temps and low quality light), which can occur in either late summer or early spring, need to be avoided in a production greenhouse. So for best performance, encourage your growers to light the crop to at least 16 hours (night break also works), keep temperatures a bit warmer especially at soil level, and grow them in the brighter sections of the growing facility. Once we are past early spring the crop becomes even easier to grow, making it a great late-spring offering as well.
1. Like tuberous and Reiger begonias — the key to success is control of watering. Remember where these plants’ parents came from: the cliffs of Argentina. Like tuberous and Reiger begonias, these plants hate soggy soil, so remind people to keep them on the dry side with good air circulation. (The same growing conditions for Reiger and tuberous begonias.)
2. The really cool part of these begonias is that as the cuttings begin to emerge and grow, they will form flowers after about the fourth node, so flowering under long days is practically automatic. The secret is to make sure that the young plant has a strong base to support the subsequent growth and flowering, so providing the correct environment early is key to the later success of the plant. Again, this is no different than what is true for the other species of begonias. Both series are for containers, whether upright or in a hanging basket. Due to their trailing habit, they aren’t a prime garden candidate.
The Mandalays will thrive in bright sunlight, and this sets them apart from most Begonias. In the South and on the West Coast, a filtered or dappled sun location would be more apropos in the heat of the summer.
The Bellagios also tolerate bright sun early in the summer, but with their double flowers, they will perform best in a filtered sun location. Both of these Begonias require a high fertilizer rate of 200 to 250 ppm. The Bellagio Begonias, if grown lean at a lower fertility rate, will have flowers that revert from double flowers to single flowers. It is necessary to fertilize these plants in order to get the best performance.