Begonias are ornamental plants known for their diverse foliage and vibrant flowers. Originating from tropical and subtropical regions, begonias are inherently sensitive to lower temperatures. This makes cold a primary concern for their health and survival.
Begonia Cold Tolerance
Most begonia varieties flourish in a consistent temperature range between 60°F and 75°F (15°C to 24°C). Within this ideal range, they exhibit robust growth and vibrant blooms. Temperatures dropping below 60°F (15°C) can begin to induce stress. The risk of damage becomes more pronounced below 50°F (10°C), making begonias particularly vulnerable. While some types, such as wax begonias, might tolerate slightly cooler conditions, temperatures below 45°F (7°C) are generally unsustainable for most begonias.
Freezing temperatures, at or below 32°F (0°C), pose a severe threat, often leading to significant harm or plant death. Frost is especially damaging because it causes water within plant cells to freeze and expand, rupturing cell walls and leading to irreversible tissue damage. Although some specific varieties, like Begonia grandis subsp. evansiana, can demonstrate hardiness down to 32°F (0°C) in mild climates when properly mulched, most begonias require frost-free conditions outdoors. Tuberous begonias, in particular, tend to be more sensitive and necessitate warmer environments compared to some fibrous-rooted types.
Identifying Cold Damage
When begonias are exposed to cold temperatures, they exhibit several visual symptoms, which may not appear immediately but develop over hours or days. A common indicator is wilting or drooping of the leaves, even if the plant has adequate moisture. Leaves often show discoloration, turning black or brown, especially along their edges, due to cellular damage.
In more severe cases, the foliage can become soft, mushy, or translucent, signifying extensive internal damage. Stunted growth is another sign of cold stress. Leaf drop can occur, particularly if cold exposure is prolonged or extreme. Minor chilling damage might manifest as yellowing or bronzing of leaves, or a general slowing of growth, while severe frost damage typically results in widespread blackened, mushy tissue.
Protecting Begonias from Cold
Proactive measures are crucial to safeguard begonias from cold damage. Monitor local weather forecasts, especially during transitional seasons like autumn and spring, to anticipate temperature drops. For begonias growing in pots or containers, bring them indoors before outdoor temperatures fall below their tolerance, particularly when nighttime temperatures are forecast to dip into the 40s°F (4-9°C).
For begonias planted directly in the ground, covering them with frost cloths, blankets, or sheets before a cold snap provides insulation. Applying a thick layer of organic mulch around the base of outdoor plants helps insulate roots and regulate soil temperature. When bringing potted plants indoors, select a location away from cold drafts or direct exposure to cold window sills, which can create localized cold pockets. For tuberous begonia varieties, dig up the tubers before the first frost, cure them, and store them in a cool, dark, and dry place, ideally between 40-50°F (4-10°C), nestled in peat moss or sand until the next growing season.
Recovering Cold-Damaged Begonias
When a begonia has experienced cold damage, assess the extent of the harm. If the plant is outdoors, move it to a warmer, more stable indoor environment immediately to prevent further stress. Carefully prune away any plant material that is visibly dead, blackened, or mushy, using clean, sharp pruning shears.
After cold exposure, begonias become susceptible to root rot, so adjust watering practices. Avoid overwatering; allow the soil to dry out considerably between waterings. Refrain from fertilizing a cold-damaged begonia immediately, as this can stimulate tender new growth vulnerable to further cold or stress. Wait until the plant shows clear signs of new growth before applying a diluted, balanced fertilizer. Patience is essential during the recovery process, as it can take several weeks or even months for a begonia to bounce back from cold damage.