Canna lilies are vibrant, herbaceous perennials that bring a dramatic, tropical aesthetic to the summer garden. As subtropical plants, cannas grow from thick, fleshy underground stems known as rhizomes, not true bulbs. For gardeners in USDA hardiness zones 8 or 9 and colder, these rhizomes are sensitive to freezing temperatures and cannot be left in the ground to survive the winter. To enjoy these striking flowers again next season, you must lift the rhizomes from the soil and properly store them until spring returns, preventing the tissue damage that sub-freezing soil temperatures would cause.
Recognizing the Ideal Time to Lift
Determining the precise moment to lift canna rhizomes is entirely dependent on environmental cues, with the goal being to maximize the energy stored in the rhizomes. Throughout the growing season, the foliage produces the starches and sugars that the rhizome needs to overwinter successfully. It is beneficial to keep the plants in the ground for as long as possible in the fall, allowing this energy transfer to complete.
The first light frost is the universal signal to begin preparing for the lifting process. A light frost causes the foliage to visibly change color, often turning yellow or blackening the edges of the leaves. This initial freeze is not severe enough to penetrate the soil and damage the rhizomes, but it triggers the plant’s natural process of entering dormancy. Once the foliage is fully blackened and collapses, the plant has signaled that the maximum amount of energy has been pulled down into the rhizomes for storage.
Waiting for this natural dieback is superior to digging prematurely, but you must act with urgency once the initial frost occurs. A second, harder freeze will often penetrate the soil, potentially freezing and killing the shallowly planted rhizomes. The ground itself must not be allowed to freeze solid before the lifting occurs, as this makes the process nearly impossible and significantly increases the risk of plant death.
Step-by-Step Digging and Cleaning
The first step involves cutting the stems back significantly, leaving a short handle of about two to six inches above the soil line. This remaining stem provides a convenient point to grasp and maneuver the heavy clump. Using a garden fork instead of a spade is recommended, as the tines are less likely to slice into the brittle, fleshy rhizomes.
Carefully insert the fork several inches away from the base of the stem, circling the entire clump to loosen the soil around the extensive root system. Gently pry the entire root ball upwards, taking care to avoid snapping the rhizomes, which are often shallowly rooted. Once lifted, gently shake off the majority of the clinging soil and rinse the rhizomes with a hose to remove any remaining dirt. Clean surfaces allow for a thorough inspection to ensure no pests or signs of disease are present before storage.
After cleaning, the rhizomes require a brief curing period to prepare them for long-term storage. Place the clumps in a cool, sheltered, and well-ventilated area for approximately one week. An ideal curing temperature is warm, ranging from 70 to 80 degrees Fahrenheit, which allows the outer tissue to dry and form a protective layer. This curing helps seal any minor cuts or abrasions, reducing the chance of rot during the winter months.
Proper Storage for Winter Survival
After the curing period, the rhizomes are ready for their long winter dormancy in a protected environment. The ideal storage location must be cool and dark, maintaining a consistent temperature range between 40 and 50 degrees Fahrenheit. Temperatures below freezing will kill the rhizomes, while temperatures consistently above 50 degrees may encourage premature sprouting. A cellar, cool basement corner, or temperature-controlled shed often provides the required conditions.
The storage environment should be moderately humid, ideally around 40 to 50 percent, to prevent desiccation. To maintain the proper moisture balance, the cured rhizomes should be packed in a breathable medium like peat moss, vermiculite, or sawdust. Place a layer of the medium in a cardboard box or plastic bin, arrange the rhizomes so they are not touching one another, and then cover them completely with more medium.
Ensure the container is not airtight, as good air circulation is necessary to prevent the buildup of moisture that leads to fungal growth and rot. Throughout the winter, periodically check the stored rhizomes for any signs of trouble. If a rhizome appears shriveled or wrinkled, the storage medium is too dry and needs a light misting. Conversely, if you notice soft, mushy spots, the medium is too wet, and the affected rhizome should be removed to prevent the decay from spreading to others.