Canna lilies are plants native to tropical and subtropical regions, making them highly sensitive to cold temperatures. In climates that experience freezing winters, these herbaceous perennials cannot survive in the ground and are instead grown as annuals or container plants. Overwintering is the process of preserving the plant’s underground storage structure, known as a rhizome, so it can be successfully replanted the following season. This preservation allows gardeners to enjoy the canna year after year without needing to purchase new stock each spring.
Timing the Harvest and Digging Up the Rhizomes
The signal to begin the harvest process is the arrival of a killing frost in the autumn. This frost causes the canna’s foliage to die back, which is a cue for the plant to halt above-ground growth. The plant then transfers its remaining energy and starches down into the fleshy rhizomes for winter survival before dormancy.
Cut the stalks back to a height of four to six inches above the soil line before digging. Use a pitchfork or a spade to loosen the soil in a wide circle, starting at least eight to ten inches away from the base of the stem to avoid damaging the brittle rhizome clump. Carefully lift the entire clump from the ground, taking care not to cut or bruise the organs, as wounds can serve as entry points for disease during storage.
Curing and Cleaning for Dormancy
Once the rhizome clumps are out of the ground, the goal is to prepare them for a state of rest. Begin by gently shaking off the majority of the soil, but avoid using a strong hose spray or scrubbing the surface vigorously. Excessive washing can introduce moisture, increasing the risk of rot during the dormant period.
The next step is curing, which involves allowing the rhizomes to air-dry for several days in a protected, shaded area. A well-ventilated garage or shed with temperatures between 60°F and 80°F is ideal. This drying period toughens the outer skin, allowing any minor cuts or scrapes to seal, which is a natural defense against moisture loss and pathogens during storage.
Maintaining Optimal Storage Conditions
Store the cured rhizomes in a location where temperatures remain cool but reliably above freezing, ideally within a range of 40°F to 50°F (4°C to 10°C). Temperatures warmer than 50°F can prematurely break dormancy, causing the rhizomes to sprout before it is safe to plant them outdoors.
The rhizomes should be packed in a moisture-retentive medium without promoting mold growth. Suitable packing materials include:
- Dry peat moss
- Vermiculite
- Wood shavings
- Shredded newspaper
Place the rhizomes in a cardboard box, paper bag, or open plastic tote, ensuring they do not touch each other, then cover them completely with the chosen medium. Storing them in a breathable container, rather than a sealed plastic bag, allows for air circulation and prevents rot.
Throughout the winter, periodically check the stored rhizomes for signs of distress, usually once every three to four weeks. A healthy rhizome should remain firm and plump; if it appears shriveled or wrinkled, the storage medium is too dry and needs a light misting of water. Conversely, any rhizomes displaying soft spots or mold should be immediately removed and discarded to prevent the spread of decay.
Reintroduction to the Garden in Spring
Waking the rhizomes from dormancy typically begins four to six weeks before the last expected frost date. First, separate the clumps by hand or with a sharp, sterile knife, ensuring each resulting section contains at least one visible growth bud, often called an “eye.” Discard any pieces that are soft, mushy, or completely dried out.
To give your cannas a head start on the growing season, plant the sections in pots filled with potting mix and place them in a bright, warm location indoors. Keep the soil lightly moist, and the warmth will encourage the eyes to sprout. Once all danger of frost has passed and the soil temperature outdoors has warmed to at least 60°F, the plants can be transplanted into the garden. If you prefer not to start them indoors, you can plant the dormant rhizomes directly into the ground once the soil is warm, which will result in new growth appearing later.