The first time I saw a flowering winter begonia, I didn't actually recognize it as a begonia. I was used to the wax begonias, with their smallish flowers, or the Rex begonias, with their enormous leaves. Known as Rieger begonias, these beautiful flowering winter plants have creamy, beautiful blooms in bright yellows, reds, pinks, and even white. They are typically bred to bloom during the winter season and sold as disposable plants—the idea is to enjoy the bloom and throw them out after the season is over.
But you needn't follow this rule: you can grow Rieger begonias year-round and enjoy their blooms next fall.
- Light: Bright, indirect light year-round. They are photoperiod bloomers, meaning the bloom is stimulated when the number of hours of light they receive drops.
- Water: Let the top 1/2" dry between waterings. After blooming, let the plant almost dry out and cut back all the foliage.
- Temperature: Average to warm (and humid). They can go as low as 60˚F at night in the fall to help stimulate a bloom.
- Soil: Airy, light, fast-draining soil.
- Fertilizer: Use liquid fertilizer weekly at quarter strength or biweekly at half strength. In the fall, switch to a high-phosphorous fertilizer to encourage bigger blooms.
Most growers recommend that people throw out their Rieger begonia after the first bloom is over. And from a financial point of view, that makes perfect sense for the growers.
Like other begonias, however, the Rieger's begonia readily propagates from leaf-tip cuttings, so it seems a shame to throw away a plant that wants only for a short dormant period and can be quickly and easily propagated into a host of new plants. The best time to take cuttings is after the bloom is over and the plant has been cut back when the new growth begins to emerge in the spring.
Use a seed-starting mix and keep the cuttings evenly moist.
Even people who keep Rieger begonias frequently don't repot the parent plant. Instead, after the dormant period is over and the plant has begun to regrow, you can cut off the new leaves and propagate them as leaf-tip cuttings, then discard the parent plant. Alternatively, you can only take some of the new growth for propagation and let the parent plant grow out again (its bloom the following year might not be as spectacular). When repotting a Rieger begonia, only increase the pot size as much as necessary. These plants like to be slightly pot-bound.
The Rieger begonia is also known as the Begonia x hiemalis, or hiemalis begonia. The original plant was a cross between a standard wax begonia and a tuberous begonia and has since evolved into a thriving category of its own. They are also sometimes called elatior begonias, although this is the same plant as the Rieger begonia. Today, the flower variety is achieved by crossing existing hybrids with each other and standardizing for color.
The main joy of a Rieger begonia is its lovely flowers, so look for new plants with lots of unopened, tight and healthy buds.
As old flowers are spent, pinch off the flowers to encourage new blooms to open. After the plant is done blooming, cut it back and let it dry out, then move it to a bright place and begin watering again when the weather warms up. Never let your Rieger begonia sit in water or spray the leaves directly with water. Both of these can encourage diseases than will kill the plant.