Begonias are popular for their vibrant colors and lush foliage in gardens and containers worldwide. Whether these plants return year after year depends entirely on the climate and the specific structural type of the begonia. Although botanically classified as perennials, their survival is dictated by extreme sensitivity to cold temperatures. Understanding this difference between classification and practical treatment is key to keeping these tropical plants blooming for multiple seasons.
The Climate Factor: Annual vs. Perennial
Begonias are designated as tender perennials, meaning they live for more than two years but cannot tolerate freezing temperatures. Their native environment is typically tropical or subtropical, where frost is nonexistent. In warm, frost-free regions, such as USDA Hardiness Zones 10 and 11, begonias reliably return each spring and behave as true perennials.
In most North American and European gardens, winter temperatures drop below freezing, which is lethal to the plant’s tissues. Because they die back in the cold, gardeners in temperate zones treat begonias as annuals. Survival requires human intervention, such as moving the plants indoors or storing their underground structures.
Understanding Begonia Types and Survival
Successfully overwintering begonias requires identifying which of the three main structural groups the plant belongs to, as each stores energy differently.
Tuberous begonias are characterized by a fleshy, underground storage organ called a tuber, which allows the plant to enter natural dormancy. The tuber stores energy and moisture, acting as a survival mechanism while the above-ground foliage dies back.
Fibrous-rooted begonias, often called wax or bedding begonias, possess only fine, thread-like roots and lack a substantial storage structure. Since they cannot enter true dormancy, these types must maintain active growth year-round to survive. Rhizomatous begonias, including many Rex types, feature thick, creeping stems (rhizomes) that grow horizontally near the soil surface. These rhizomes store nutrients but, like fibrous types, require protection from severe cold to keep their foliage alive.
Overwintering Tuberous Begonias
Saving tuberous begonias relies on inducing and managing their natural dormancy cycle. Before the first hard frost, or when the foliage naturally yellows, reduce watering to encourage the plant to direct energy into the tuber. Once a light frost has caused the foliage to die back, or the stems are cut to one inch above the soil, the tubers can be carefully dug up.
The tubers require a curing period to dry out the outer skin and prevent rot during storage. This involves letting them air-dry in a cool, dark, and dry location for one to three weeks. After curing, gently remove any remaining soil and dust the tubers with a fungicide or sulfur powder to deter mold.
They are best stored in a breathable medium like peat moss, vermiculite, or sawdust, placed in a cardboard box or paper bag. The ideal storage environment is dark, dry, and cool, with a consistent temperature range of 40 to 50 degrees Fahrenheit, ensuring the tubers remain dormant but do not freeze.
Saving Fibrous and Rhizomatous Begonias
Fibrous and rhizomatous begonias do not go dormant and must be overwintered as actively growing houseplants. Before night temperatures consistently drop below 50 degrees Fahrenheit, bring the plants indoors. Prior to moving them inside, inspect the foliage thoroughly and treat for any pests to prevent their spread within the home.
These begonias thrive best in a location that provides bright, indirect light, such as a south-facing window. They are sensitive to cold drafts or dry heat vents. Water should be reduced during the winter, allowing the top layer of soil to dry out between waterings, as the plants are in a period of less vigorous growth.
Alternatively, cuttings can be taken from fibrous types before the frost and rooted in water or potting mix, creating new plants for the following season.