Canna lilies are vibrant, tropical-looking plants known for their bold foliage and striking flowers, typically blooming from June to October. Understanding their temperature requirements is crucial for successful growth, as they are sensitive to temperature fluctuations.
Optimal Growing Temperatures
Canna lilies thrive in warm conditions, preferring temperatures between 59°F and 100°F (15°C to 38°C) for vigorous growth and abundant blooms. An ideal range for sprouting and active development is 65°F to 80°F (18°C to 27°C). Consistent temperatures promote strong growth and continuous flowering.
Both air and soil temperatures are important. Soil temperature is particularly significant for rhizome sprouting, requiring soil that is 60°F (15.5°C) or warmer before planting. Planting in warm soil ensures rhizomes sprout quickly and establish effectively.
Canna Lily Cold Tolerance
Canna lilies are sensitive to cold temperatures and frost. While hardy in USDA Zones 7-10, prolonged exposure below 50°F (10°C) inhibits growth, and frost causes foliage to blacken and die back. Temperatures below 15°F (-10°C) can lead to browning and wilting leaves, potentially affecting the rhizomes. If temperatures drop below -15°C (5°F), there may be a decrease in sprouting or even a complete failure to sprout in the spring.
In colder climates, cannas enter a dormant cycle to survive the winter. This dormancy protects the rhizomes from freezing temperatures, which can cause internal damage and prevent future growth. Cold exposure can cause superficial foliage damage or irreversible harm to the rhizomes, impacting the plant’s ability to regrow.
Canna Lily Heat Tolerance
Canna lilies perform well in high temperatures, thriving up to 90°F (32°C) and blooming vigorously even in intense summer heat. However, extreme or prolonged heat can still cause stress, particularly when temperatures exceed 100°F (38°C).
Signs of heat stress include wilting leaves, reduced flowering, and dull foliage. When temperatures surpass 109°F (43°C), leaves may lighten in color, curl, become susceptible to sunburn, and in severe cases, the entire plant may wilt and dry out. While cannas can tolerate some heat, consistent moisture is important to mitigate stress in hot conditions, which helps prevent wilting and maintain overall plant health.
Protecting Cannas from Temperature Extremes
Protecting canna lilies from temperature extremes is important for their long-term health and vibrant display. In marginal zones, such as USDA Zone 7, a thick layer of straw or leaf mulch can protect in-ground rhizomes from cold after the foliage dies back. For colder regions (USDA Zones 6 and below), digging up and storing rhizomes indoors is a common practice. After the first frost blackens the foliage, cut the plants back, carefully dig up the rhizomes, and allow them to dry for a few days to prevent rot.
Store them in a cool, dark, and dry place with temperatures between 40°F and 50°F (4°C and 10°C), typically in peat moss, sawdust, or vermiculite, ensuring they do not touch each other to prevent mold. Container-grown cannas offer convenience, as they can be moved indoors to a frost-free location, such as a garage or basement, for winter.
To protect cannas from excessive heat, strategic placement is beneficial, such as providing afternoon shade in very hot climates to prevent leaf scorch. Adequate watering is crucial during hot spells, ensuring the soil remains consistently moist but not waterlogged. Mulching around the plants helps regulate soil temperature, keeping the root zone cooler, and aids in retaining soil moisture. These measures help prevent heat stress, allowing cannas to continue thriving and blooming throughout the summer.