Canna lilies, often mistakenly called bulbs, actually grow from thick, fleshy underground stems known as rhizomes. These tropical plants thrive in warm climates, but their rhizomes cannot tolerate prolonged freezing temperatures. Gardeners in temperate zones, typically USDA Hardiness Zone 7 and colder, must lift these storage organs before winter to ensure the plant’s survival and vigor for the following growing season.
Knowing When to Lift Canna Rhizomes
The timing for lifting Canna rhizomes is governed by the plant’s natural response to cold temperatures. The most important signal is the first hard frost, which occurs when air temperatures drop below 28°F (-2°C) for a sustained period. This temperature drop triggers the plant to cease active photosynthesis and move stored carbohydrates from the foliage back into the underground rhizome for winter survival.
Visually, this transition is confirmed when the lush green leaves and stems turn noticeably black or dark brown, indicating the complete dieback of the top growth. Waiting until after this initial frost ensures the plant has successfully transferred all necessary energy reserves. Lifting the plant before this energy transfer is complete can result in a poorly nourished storage organ that struggles to break dormancy in the spring.
The Process of Digging and Preparing the Rhizomes
Begin the preparation process by using clean, sharp pruning shears to cut back the thick foliage and stems. Reduce the stems to about four to six inches above the soil line. These remaining stalks act as handles and indicators of the rhizome’s precise location, minimizing the size of the clump and making the lifting process more manageable.
To avoid puncturing the fleshy rhizomes, use a garden fork or a flat-tined spade, positioning the tool approximately six to twelve inches away from the remaining stalks. A garden fork is often preferred because its tines are less likely to accidentally sever the underground storage organs. Gently push the tool straight down into the soil, working it completely around the plant clump to loosen the surrounding earth.
Insert the tool straight down initially, then angle it slightly inward beneath the root ball before applying upward pressure. This technique lifts the entire root mass intact, preventing unnecessary wounds that could become entry points for decay organisms. Carefully lift the entire mass of soil and rhizomes from the ground, using the remaining stalks for leverage.
Once the clump is out of the ground, gently shake off the majority of the heavy, clinging soil and debris. For stubborn dirt, use a gentle stream of water from a hose to wash away the remaining material. It is important to remove the bulk of the soil, as excessive moisture can encourage mold or fungal growth during the storage period.
Examine the lifted rhizomes closely for any signs of damage, soft spots, or rot. Any parts that appear mushy, discolored, or diseased should be cleanly cut away using a sterilized knife or shears to prevent the spread of pathogens. Large, dense clumps can be separated into smaller sections at this stage, ensuring each piece retains at least one visible growth “eye” or bud for spring regeneration. After cleaning and trimming, the rhizomes are ready for the initial drying or “curing” phase.
Ensuring Successful Winter Storage
Following cleaning, rhizomes must undergo a short curing period to prepare them for long-term dormancy. Place the cleaned rhizomes in a dry, dark, and well-ventilated area for approximately three to five days. This brief drying time minimizes the risk of moisture absorption and subsequent rot.
Long-term preservation requires a storage environment that is consistently cool but reliably above freezing temperatures. The ideal temperature range is between 40°F and 50°F (4°C to 10°C), conditions often achievable in unheated cellars or insulated garages. Temperatures above 50°F may encourage premature dormancy break, while freezing temperatures will cause cellular damage.
To prevent desiccation over the winter, the rhizomes must be nested in a breathable storage medium that provides insulation and humidity control. These materials help maintain a stable, low-humidity microenvironment:
- Dry peat moss
- Wood shavings
- Vermiculite
- Slightly dampened sand
Place the rhizomes in a container that allows air circulation, such as a cardboard box, a mesh bag, or a plastic tote with ventilation holes punched in the sides.
The rhizomes should be layered within the medium, ensuring they are not directly touching each other, which reduces the chance of rot spreading. Throughout the storage period, the rhizomes should be checked periodically, perhaps once a month. Inspect the material for signs of excessive shriveling, which indicates dryness, or the presence of mold, which suggests overly humid conditions. If the medium appears too dry, a light misting can provide minimal moisture, but if mold is present, increase air circulation and replace the storage medium entirely.