Bougainvillea, known for its vibrant, papery bracts, is a popular choice for adding tropical color to gardens. Originating from warm South American climates, this plant is sensitive to cold temperatures, making understanding its tolerance important.
Understanding Bougainvillea’s Cold Sensitivity
Bougainvillea thrives in warm environments, ideally between 60°F and 90°F (15°C to 32°C), where it exhibits vigorous growth and abundant flowering. However, it is not frost-tolerant. When temperatures drop below 40°F (4°C), damage can begin. Below 32°F (0°C) poses a significant risk, causing light or extensive damage, particularly to outer and upper branches. Prolonged exposure below 30°F (-1°C) can cause severe damage or be lethal, especially if the ground freezes and damages the root system.
Several factors influence cold tolerance. The duration of cold temperatures is important; shorter cold snaps are less damaging than prolonged freezes. Wind and humidity also impact tolerance, with cold, windy conditions increasing damage. Older, established plants are more resilient than newly planted ones due to larger root systems. Bougainvillea is hardy in USDA Zones 9b through 11.
Protecting Bougainvillea from Cold Temperatures
To protect bougainvillea from cold, move potted plants indoors before frost. Bring them inside when temperatures consistently drop below 40°F (4°C), placing them in a bright location above 60°F (15°C) if possible.
For ground-planted bougainvillea, cover them with protective materials like burlap or frost cloths when freezing temperatures are expected. These covers should be removed daily if temperatures rise to prevent overheating and allow air circulation.
Apply a 3 to 6-inch layer of mulch, such as straw, leaves, or shredded bark, around the base of the plant. This insulates the roots from freezing temperatures, especially for larger plants where full covering is impractical.
Ensure the plant is well-hydrated before a freeze. Moist soil retains heat better than dry soil, insulating the roots. Plant bougainvillea near a warm wall or in a sheltered courtyard for natural protection from cold winds and to retain warmth.
Recognizing and Addressing Cold Damage
After cold exposure, bougainvillea may show wilting, browning or blackening leaves, and mushy stems. The plant may appear dead, with foliage remaining on branches even after freezing.
Exercise patience when assessing damage. Often, only outer branches and foliage are affected, while roots remain unharmed, allowing recovery. Wait until spring or after the last frost, when evening temperatures consistently warm above 40°F (4°C), to assess which parts are truly dead.
Once new growth emerges, prune damaged sections. Cut back dead or severely damaged branches to healthy wood, identified by green tissue when scratched. Pruning stimulates new growth and helps restore the plant’s shape. Multiple pruning sessions may be necessary for vigorous regrowth. After pruning, provide adequate watering (without overwatering) and light fertilization once new growth is established to aid recovery.