Begonias are tropical and subtropical natives, beloved for their vibrant blooms and striking foliage. Since they cannot withstand freezing temperatures, they require special care to survive the dormant season. Successful winter care depends on your local climate and, most importantly, the specific type of begonia you are growing. Understanding the plant’s root structure is the first step in determining if it needs to be brought indoors or forced into a period of rest to ensure its return next spring.
Identifying Your Begonia Type
The primary distinction for winter survival lies in the begonia’s root system, which determines its seasonal behavior. Tuberous begonias grow from a thick, rounded underground storage organ. This structure allows them to enter a natural state of dormancy when conditions become cold or dry. These varieties often feature the largest, most flamboyant flowers, frequently seen in hanging baskets.
Fibrous-rooted begonias, commonly known as wax or bedding begonias, possess a shallow, dense network of thin roots. They typically feature glossy leaves and smaller flowers. These types, which include cane-like varieties, have no natural dormancy period and must be kept actively growing indoors. Rhizomatous begonias, such as the Rex begonia, grow from a thick, creeping stem (rhizome) along the soil surface. They are prized for their colorful foliage and also require continuous indoor growth during winter.
Winterizing Tuberous Begonias for Dormancy
Tuberous begonias must be lifted and stored where the ground freezes, as the tubers cannot survive temperatures below 45°F. In the fall, stop watering and allow the foliage to naturally yellow and die back, which signals the plant to transfer energy to the tuber. Once a light frost has blackened the leaves, or the foliage has withered, cut the stems back to a few inches above the soil line.
Carefully lift the tubers, avoiding damage to the fleshy tissue. After shaking off loose soil, cure them in a cool, dry location for one to two weeks, allowing the outer skin to dry and thicken. Curing prevents rot during storage by closing wounds. Once cured, remove any remaining roots or stem material and dust the tubers with a fungicidal powder, such as sulfur, to prevent disease.
The cleaned tubers should be stored in a medium like dry peat moss, vermiculite, or sawdust, which provides insulation and wicks away moisture. Place them in a cardboard box or paper bag, ensuring they are covered by the packing material and not touching each other. The ideal storage location is dark, dry, and cool, with a consistent temperature range of 40°F to 50°F, such as a cool basement. Regularly check the tubers for signs of shriveling (low humidity) or softness and mold (excess moisture).
Keeping Fibrous and Rhizomatous Begonias Indoors
Fibrous and rhizomatous begonias must be moved indoors before nighttime temperatures drop below 50°F, as they do not go dormant. Before the move, thoroughly inspect the plants for pests like spider mites or mealybugs, which spread rapidly indoors. A gentle wash with a mild insecticidal soap can eliminate any pests.
Once indoors, these begonias need bright, indirect light to compensate for reduced winter sunlight. A spot near an east-facing window or a few feet from a south or west-facing window is suitable. Supplemental full-spectrum grow lights may be needed for 8 to 10 hours daily to maintain healthy growth. Indoor environments, especially with forced-air heating, often have low humidity, which can cause leaf drop and browning.
To raise local humidity, place the pots on a shallow tray filled with pebbles and a small amount of water, ensuring the bottom of the pot does not sit directly in the water. Watering frequency must be significantly reduced during the winter months compared to the summer growing season. Allow the top inch of the soil to dry out completely before watering, as overly wet soil is the primary cause of root rot.
Transitioning Begonias Back to Spring
The transition back to active growth begins indoors several weeks before the last expected frost date. For stored tuberous begonias, this is typically six to eight weeks before they can be moved outside. Check the tubers for damage, then plant them concave-side up in shallow containers filled with fresh, well-draining potting mix.
Place the newly potted tubers in a warm area, ideally around 70°F, and water lightly to encourage new shoots. Once the shoots have developed a few leaves, treat them as growing plants, gradually increasing light and water.
For fibrous and rhizomatous begonias kept indoors, the transition involves preparation and hardening off. Prune any leggy or weak growth developed over the winter to encourage a bushier, more robust shape. Begin hardening off by moving the plants outdoors to a sheltered, shady location for a few hours each day, gradually increasing the time spent outside. This slow acclimation to sun, wind, and outdoor temperatures prevents leaf scorch and shock, ensuring they are ready for their permanent spot once all danger of frost has passed.