Begonias are a diverse group of ornamental plants prized for their vibrant foliage and delicate flowers. When gardeners ask if these plants are “hardy,” the answer is complicated because the genus Begonia encompasses over 2,000 species and countless hybrids. The term “begonia” does not refer to a single type of plant with uniform cold tolerance. Understanding whether a begonia can withstand winter depends entirely on its specific classification and the local climate.
Why “Begonia” Isn’t a Single Answer: Defining Hardiness and Types
In horticulture, “hardy” refers to a plant’s ability to survive the winter season outdoors without specialized protection. This survival is typically measured using the USDA Plant Hardiness Zone map, which divides North America into zones based on the average annual minimum winter temperature. A plant is considered perennial or hardy in a specific zone if it can reliably withstand the lowest temperatures experienced there.
Begonias originate primarily from tropical and subtropical regions, meaning most species are unsuited for freezing temperatures. To manage the vast diversity within the genus, horticulturists categorize begonias into major groups based on their root structures. These structural differences dictate the plant’s overall growth habit and its survival mechanism during cold periods.
The three primary classifications are Tuberous, Fibrous (or Wax), and Rhizomatous begonias. Tuberous begonias grow from a swollen underground stem structure that serves as a food storage organ and allows for dormancy. Fibrous begonias develop a traditional, thread-like root system without specialized storage organs. Rhizomatous begonias grow from a thick, creeping stem, or rhizome, that typically rests on or just below the soil surface. These distinct physical characteristics determine how each type reacts to a drop in temperature.
Specific Cold Tolerance Based on Begonia Classification
Fibrous begonias, commonly known as wax begonias (Begonia semperflorens), have the lowest cold tolerance among the main groups. Their foliage and fine root systems are killed when temperatures dip below 32°F (0°C). Consequently, they are treated as annuals in most temperate climates, surviving year-round only in USDA Zones 9 or 10 and warmer.
Tuberous begonias (Begonia tuberhybrida) use a different survival strategy, though their above-ground growth is tender. The foliage quickly succumbs to the first frost, signaling the plant to enter its mandatory dormant period. Survival depends entirely on the underground tuber, which can tolerate soil temperatures slightly above freezing, perhaps down to 35°F (1.7°C), provided the soil is dry.
While the tuber technically makes them perennial, this is only practical in mild, dry winter climates, typically Zone 8 and higher, where the ground does not freeze solid. In colder regions, the plant must be lifted and stored to prevent moisture and freezing temperatures from causing the tuber to rot or freeze. This dormancy is a biological requirement for subsequent spring growth.
Rhizomatous begonias, including popular Rex begonias, possess an intermediate level of cold tolerance. They are frost-tender, and their fleshy leaves and stems are damaged by temperatures near freezing. The thick, creeping rhizome can sometimes survive short cold snaps if the plant is protected, such as when grown against a warm structure or in a sheltered spot.
These types are rarely grown outdoors year-round outside of Zones 10 and 11, and they are overwhelmingly cultivated as houseplants. Even brief exposure to temperatures below 40°F (4.4°C) can cause significant leaf damage, restricting their outdoor use to summer months.
Practical Steps for Overwintering Begonias
Since most begonias cannot survive temperate winters outdoors, gardeners must intervene to preserve their plants for the following season. The procedure differs significantly based on the plant’s structure. Tuberous begonias require management of their dormancy to ensure survival.
The overwintering process for tubers begins immediately after the first light frost signals the foliage to die back. Gardeners should wait until the leaves have yellowed before carefully lifting the tubers from the soil. They should be left in a dry, shaded location for several days to cure. This curing allows the outer skin to harden and moisture to evaporate, preventing fungal diseases during storage.
Once cured, the tubers should be cleaned of excess soil, but fine roots should be left attached. They are then stored in a cool, dark, and moderately humid environment, ideally between 40°F and 50°F (4.4°C and 10°C). Storing the tubers in a medium like dry peat moss, vermiculite, or sawdust provides insulation and helps maintain consistent humidity, preventing shriveling or rotting.
For fibrous and rhizomatous begonias, the strategy shifts to indoor cultivation, as they do not require dormancy. Potted plants must be brought inside well before the first frost, ideally when nighttime temperatures consistently drop below 50°F (10°C). Before moving them indoors, a thorough inspection for pests is necessary to prevent infestations.
Once inside, these tropical varieties thrive in bright, indirect light, such as near an east or south-facing window. During the shorter winter days, the plants’ metabolic rate slows down, requiring reduced watering frequency. Allowing the top inch of soil to dry out between waterings helps prevent root rot, ensuring the plant remains healthy until it can be safely returned outdoors in spring.