Begonias include flowering- and foliage-type plants of more than 1,000 species. Begonias are warm-weather plants but survive through the winter if kept indoors in storage or as houseplants. Begonias don't suffer many problems, but the plants are vulnerable when it comes to water. They struggle with too little water, and disease issues arise when they are overwatered.
Lack of Moisture
While wax begonias tolerate drought better than other varieties, all begonias require a moist -- but not wet -- well-drained soil. If planted in a clay container, your plant may be losing moisture too quickly. Clay pots wick moisture away from the soil. Do not water on a strict schedule but by the feel of the soil. The Clemson Cooperative Extension recommends watering your plants evenly, allowing the soil to dry slightly between waterings. Reduce the amount of water provided in winter. Use less fertiliser. Begonias require feeding only with every other watering. Use a balanced, half-strength fertiliser moderately applied.
Too Much Moisture
Angel wing begonias, a type of cane-stemmed begonia, do not tolerate hot, dry conditions. However, these begonias develop mildew disease when overwatered. The infection leads to spotting of the leaves and subsequent drying of foliage. The North Dakota State University Extension suggests treating this condition by improving the air circulation around your plants and removing damaged leaves. Do not mist the foliage of begonias.
Even though begonias with variegated foliage need more light, keep foliage begonias, such as rex begonias, out of direct sunlight. While foliage begonias generally perform better under humid conditions, rex begonias require humidity levels of 50 per cent or higher, or you your plants risk developing leaves with brown edges and a crispy texture, according to the University of Illinois Extension. This humidity level may be difficult to attain indoors in winter when the air dries out. Water-filled trays around your plants increase humidity, but do not set the plant pots in the water.
Allow some begonias to dry down for winter storage, including tuberous begonias. As fall approaches, begin reducing the amount and frequency of water until the leaves dry and the stems wither. Overwinter the tubers in a dry peat or vermiculite at a temperature range of about 7.22 to 12.7 degrees C. Take them out in the spring, gradually increase the water you give them and expose them to indirect light.