Canna lilies, with their vibrant blooms and striking foliage, bring a tropical flair to any garden. Their large leaves and showy flowers in shades of red, orange, yellow, and pink make them a focal point in landscapes or containers. Successful cultivation requires understanding their needs in relation to your local climate, especially through plant hardiness zones.
Understanding Plant Hardiness Zones
Plant hardiness zones provide a system for gardeners to determine which plants thrive in a particular location. The USDA Plant Hardiness Zone Map, the most recognized system in the United States, divides the country into zones based on the average annual extreme minimum winter temperature.
Each zone represents a 10-degree Fahrenheit temperature range, with lower numbers indicating colder climates. Zones are further divided into ‘a’ and ‘b’ subzones, representing a 5-degree difference. While this map is a valuable tool for selecting perennials that survive winter, it does not account for factors like summer heat, humidity, or precipitation, which also influence plant growth.
Canna Lily Hardiness
Canna lilies, despite their name, are not true lilies. They are tropical and subtropical plants that grow from rhizomes, which are underground stems. They are perennial in USDA Plant Hardiness Zones 7 through 10, meaning their rhizomes can remain in the ground year-round and regrow each spring.
In colder zones (below USDA Zone 7), cannas behave more like annuals. Their rhizomes are sensitive to freezing temperatures and will not survive winter if left unprotected in the ground.
Canna Care Based on Zone
Canna lily care varies significantly by hardiness zone, especially regarding winter protection.
Warmer Zones (7-10)
In warmer zones, where cannas are perennial, winter care is minimal. Gardeners typically cut back the foliage after the first frost causes it to die back, then apply a thick layer of mulch over the rhizomes for added protection, especially in Zone 7 where temperatures can fluctuate. During the growing season, cannas thrive in full sun, ideally receiving at least six to eight hours of direct sunlight daily. They prefer rich, well-draining soil that remains consistently moist, often requiring generous watering, particularly in hot climates. Apply a balanced, slow-release fertilizer in early spring and mid-summer for robust growth and continuous blooming.
Colder Zones (6 and below)
Overwintering canna rhizomes indoors is a common practice to ensure their return the following year. After the first hard frost blackens the foliage, cut the stems down to about four to six inches from the ground. Gently dig up the entire clump of rhizomes, starting about six inches away from the plant’s base to avoid damage. Shake off excess soil from the rhizomes, then allow them to dry or “cure” in a warm, dry place for one to three days. This curing process helps prevent rot during storage.
Store cured rhizomes in a cool, dark, and dry location where temperatures consistently remain between 40 and 50 degrees Fahrenheit, such as a basement, unheated garage, or cellar. They can be stored in materials like peat moss, sawdust, vermiculite, or even in paper or heavy-duty trash bags, ensuring good air circulation and preventing direct contact between individual rhizomes to minimize rot. Periodically check the stored rhizomes throughout winter; if they appear shriveled, a light misting of water can rehydrate them, but avoid making them overly damp. In spring, after all danger of frost has passed and the soil temperature reaches at least 60 to 65 degrees Fahrenheit, the rhizomes can be replanted outdoors.
Container Growing
Growing cannas in containers offers another practical solution for those in colder zones. This method allows for easier transfer of the plants indoors before the first frost. When potting cannas, use a large container with good drainage and a quality potting mix, ideally incorporating a slow-release fertilizer. Container-grown cannas can be brought inside, pot and all, and stored in a cool, dry area for winter, requiring no water until spring.