Canna Lilies are large, tropical-looking plants known for their vibrant flowers and expansive foliage, making them a popular choice for adding drama to the summer garden. Canna Lilies are classified as perennial plants, but this classification is entirely dependent on the local climate. Native to tropical and subtropical regions, their ability to return year after year is dictated by the winter temperature of their environment. In colder regions, the Canna Lily must be treated as an annual unless specific steps are taken to protect its underground structure.
The Canna Lily’s Perennial Nature: Defining Hardiness
The perennial nature of the Canna Lily is rooted in its underground storage system, a modified stem called a rhizome. This thick, fleshy rhizome functions as a food storage unit, allowing the plant to survive periods of dormancy. Since the above-ground foliage dies back while the root structure remains alive to sprout again, the Canna is botanically categorized as a herbaceous perennial.
However, the Canna Lily is specifically a “tender perennial,” meaning its rhizomes cannot tolerate freezing temperatures in the soil. The USDA Hardiness Zone system defines where the plant can be reliably left in the ground throughout winter. Canna Lilies are cold-hardy and will return on their own in Zones 7 through 10, or sometimes 8 through 11, depending on the variety and microclimate.
In these warmer zones, the foliage dies back with the first frost, signaling natural dormancy. The rhizome survives as long as the ground does not freeze solid and remains relatively dry. If the soil temperature drops low enough for the water inside the rhizome’s cells to freeze and expand, the cells will burst, and the plant will die.
Gardeners in Zones 6 and colder must treat the Canna Lily as a seasonal annual or proactively intervene to preserve the rhizome. The survival of this underground rhizome requires consistent protection from prolonged freezing temperatures.
Essential Care During the Growing Season
To ensure the Canna Lily stores enough energy for successful dormancy and regrowth, it requires specific care during the active growing season. These tropical plants thrive in full sun, needing at least six to eight hours of direct sunlight daily to produce lush foliage and blooms. Less light can cause stems to stretch awkwardly and inhibit flower production.
Canna Lilies are heavy feeders and require rich, well-draining soil amended with organic matter like compost or aged manure. While they love moisture, the soil must never be waterlogged, which could lead to rot. Consistent moisture is necessary during the summer, often requiring deep watering once a week, or more frequently in hot conditions.
They benefit greatly from a regular fertilization schedule throughout the summer. A balanced, slow-release fertilizer can be applied at planting time, supplemented with a liquid fertilizer every four to six weeks. Routine maintenance includes removing spent blooms, a process called deadheading, which encourages the plant to produce new flower buds instead of setting seed. Deadheading the entire spent flower stalk down to the next side shoot or the base of the plant maintains a neat appearance and extends the flowering season.
Managing Dormancy and Overwintering
For gardeners in colder climates, the successful continuation of the Canna Lily’s perennial cycle depends on proper overwintering. The process begins after the first light frost, which signals dormancy by causing the foliage to die back and turn brown. Waiting for this frost ensures the rhizome has stored all available energy before removal.
Once the foliage is blackened, the stems should be cut back to about four to six inches above the soil line. The entire clump of rhizomes is then carefully dug up, avoiding slicing the storage material. After lifting, excess soil is gently shaken or brushed off; washing is unnecessary and can introduce too much moisture.
The rhizomes must then be “cured” for several days in a warm, dry, and well-ventilated location, ideally between 70 and 80 degrees Fahrenheit. This curing process toughens the skin and allows wounds to heal, reducing the risk of rot or mold during storage. Once cured, the rhizomes are stored in a cool, dark, and dry environment where the temperature remains consistently between 40 and 50 degrees Fahrenheit.
They should be placed in a breathable medium, such as peat moss, dry sawdust, or coconut coir, inside a cardboard box or paper bag. Plastic containers are avoided as they trap moisture and promote rot. The storage medium helps maintain stable humidity. Stored rhizomes should be checked monthly for signs of shriveling (indicating dryness and needing misting) or for mold or rot (requiring trimming and discarding).