Canna lilies, with their vibrant blooms and lush foliage, are a popular choice for adding a touch of the tropics to gardens. Gardeners often wonder about their classification, specifically whether these striking plants are annuals or perennials. Understanding their botanical nature and how it interacts with local climates helps clarify this common question.
The Truth About Canna Lilies
Canna lilies are herbaceous perennials, meaning they die back to the ground in colder months but regrow from their rootstock in spring. They are specifically rhizomatous plants, developing from thick, fleshy underground stems called rhizomes. These rhizomes store nutrients, enabling the plant to return year after year. However, cannas are considered “tender” perennials, highlighting their sensitivity to cold temperatures. The rhizomes produce roots from their underside and shoots, known as “eyes,” from their upper surface.
Canna Lilies and Climate
While technically perennials, canna lilies are often treated as annuals in many regions due to their low tolerance for freezing conditions. In USDA Plant Hardiness Zones 8 through 11, where the soil typically does not freeze, canna rhizomes can remain in the ground year-round and will reliably return each spring. Conversely, in colder climates, generally USDA Zones 3 through 7, the ground freezes to a depth that can damage or kill the rhizomes. In these areas, canna lilies will not survive winter if left in the ground, so gardeners treat them as annuals.
Overwintering for Perennial Return
For gardeners in colder climates who wish to keep their canna lilies as perennials, overwintering the rhizomes indoors is a practical solution. The process begins after the first light frost has killed back the foliage, but before the ground freezes solid. This timing allows the plant to store maximum energy in its rhizomes for the following year’s growth.
To prepare, cut the stems back to about 4 to 6 inches above the ground, leaving a convenient handle. Carefully dig around the plant, about 6 to 12 inches away from the stem, to avoid damaging the rhizomes, which are often shallow. Gently lift the entire clump, shaking off as much excess soil as possible. Rinse the rhizomes with water to remove any remaining dirt, which helps prevent rot during storage.
After cleaning, the rhizomes need to “cure” by air-drying in a warm, well-ventilated area (around 70 to 80 degrees Fahrenheit) for approximately one week. This curing process toughens the outer skin and helps prevent fungal issues or sprouting in storage. Once cured, store the rhizomes in a cool, dark, and dry place where temperatures remain consistently between 40 and 50 degrees Fahrenheit, such as a basement or unheated garage. Place them in a cardboard box, paper bag, or mesh bag, surrounded by a dry medium like peat moss, vermiculite, or newspaper, to maintain appropriate humidity and prevent rot spread. Periodically check the rhizomes throughout winter to ensure they are not rotting or drying out excessively, removing any compromised pieces immediately.
Replanting in Spring
As spring approaches and the danger of frost has passed, typically when soil temperatures reach at least 60 degrees Fahrenheit, it is time to prepare the overwintered canna rhizomes for replanting. Before planting, inspect the rhizomes and discard any that show signs of rot or disease. If the rhizome clumps have grown significantly, they can be divided to create more plants or to prevent overcrowding, which can reduce flowering.
To divide, ensure each section has at least one or two “eyes” or growth points and some roots attached. A sharp, clean knife can be used, or larger clumps may break apart cleanly by hand. Plant the rhizomes horizontally about 1 to 2 inches deep in well-draining, rich soil, with the “eyes” pointing upwards. Spacing them 12 to 24 inches apart, depending on the variety, allows ample room for growth. After planting, water thoroughly to settle the soil around the rhizomes, and continue consistent watering as new growth emerges.