Wax begonias (Begonia x semperflorens-cultorum) are valued for their continuous, vibrant blooms and distinctive waxy foliage. These popular plants are frequently used in garden beds, borders, and containers, bringing consistent color from late spring until the first frost. Native to tropical and subtropical regions, wax begonias naturally prefer warm and humid conditions, making their sensitivity to cold temperatures a significant consideration for gardeners. Understanding their cold tolerance helps ensure their health, especially in climates outside their native range.
Wax Begonia Cold Thresholds
Wax begonias are tender perennials that thrive in USDA Hardiness Zones 9-11, but are commonly cultivated as annuals in cooler climates due to their susceptibility to cold. Temperatures below 50°F (10°C) begin to stress these plants, and prolonged exposure can lead to damage or even plant death. Freezing temperatures are lethal; frost causes the plant’s cells to freeze and rupture.
The initial signs of cold stress often appear as wilting leaves, which may also show discoloration, turning yellow or brown. Stunted growth is another indicator that the plant is feeling the chill. If temperatures continue to drop, leaves may become limp, curl, or crisp at the edges, eventually turning a darker shade, almost bruised. In severe cases, plant parts can blacken and become mushy, leading to the entire plant dying back.
Protecting Wax Begonias in Cold Weather
Preventing cold damage is important when temperatures drop. For potted wax begonias, the most effective strategy is to bring them indoors before outdoor temperatures consistently fall below 50°F (10°C). When moving them inside, select a spot that offers bright, indirect light and protection from cold drafts or heating vents, as sudden temperature fluctuations can be detrimental.
For in-ground wax begonias in borderline zones, temporary protection can be provided during unexpected cold snaps. Covering plants with frost cloths, blankets, or cloches offers a barrier against the cold. Prior to a cold snap, watering the plants in the late afternoon is beneficial, as moist soil retains heat more effectively than dry soil, providing some warmth to the root zone.
Addressing Cold Damage
If wax begonias have already experienced cold stress or frost damage, patience and proper care can aid in recovery. It is best to assess the full extent of the damage once temperatures have warmed up and the plant’s condition is clearly visible. Any parts of the plant that appear mushy, blackened, or severely discolored should be carefully pruned away using clean, sharp shears.
Removing damaged foliage and stems encourages the plant to direct its energy towards new, healthy growth. During this recovery period, ensure the plant is in a warm location with appropriate light, but avoid overwatering, as cold-damaged plants are more susceptible to root rot. While recovery can take time, if the cold exposure was not too severe, the plant may bounce back, potentially even from the roots.