Supertunias are popular flowering annuals, cherished for their continuous, vibrant blooms from spring until the first hard frost. Known for vigorous growth, they fill containers, hanging baskets, and garden beds with color. While Supertunias offer impressive performance and heat tolerance, their vulnerability to cold temperatures is a frequent concern. Understanding their cold sensitivity is key to preserving their beauty and longevity.
Supertunia Cold Sensitivity
Supertunias are classified as tender annuals in most climates. They are sensitive to temperatures below 40°F (4°C) and can suffer damage when temperatures drop below 32°F (0°C). While they can tolerate brief exposures to temperatures in the high 30s once acclimated, prolonged chill significantly stresses the plants.
A light frost, where temperatures hover just below freezing for a short period, can cause some damage to the foliage. However, a hard freeze, typically defined as temperatures at or below 28°F (-2°C) for several hours, can be much more destructive. Such conditions can lead to widespread cellular damage, potentially compromising the entire plant. Even without visible frost, a sudden and dramatic drop in temperature can induce cold shock, impacting plant health.
Recognizing Cold Damage
When Supertunias experience cold damage, several visual symptoms appear. Leaves may wilt or droop, losing their firm structure. Discoloration is common, with affected foliage turning black, brown, or developing purple or bronzed hues. The plant material’s texture can also change, becoming soft or mushy to the touch, especially stems and flowers, indicating cellular rupture. The damage extent depends on the severity and duration of cold exposure.
Strategies for Cold Protection
Protecting Supertunias from cold temperatures can significantly extend their blooming season. For container-grown Supertunias, move them to a sheltered location like under house eaves, on a covered porch, or temporarily indoors. Ensure containers are not directly exposed to open skies or harsh winds.
For in-ground Supertunias, cover them before a predicted frost. Lightweight frost cloths, old sheets, blankets, or burlap can be draped over the plants, ensuring covers extend to the ground to trap heat. Remove covers during the day if temperatures rise above freezing for air circulation and sunlight.
Beyond covering, soil preparation offers protection. Thoroughly water Supertunias before a freeze, as moist soil retains heat better than dry soil. Applying mulch around the base of in-ground plants insulates the root system, regulating soil temperature.
Post-Cold Recovery and Care
After a cold event, caring for Supertunias requires patience and careful assessment. Wait until the threat of frost has passed and temperatures have stabilized before evaluating the full extent of damage, as some symptoms may not appear for several days. Once the plant’s condition is clear, prune away any damaged parts like blackened or mushy leaves and stems. Use clean, sharp shears to avoid further stress or disease. Even if upper growth is severely affected, the root system might still be viable, especially if the plant was established. New growth may emerge from the base with improved conditions. During recovery, provide light watering to maintain consistent soil moisture without over-saturating, and avoid heavy fertilizers that could stress the plant.