Iris rhizomes are thick, fleshy, underground stems that store nutrients for the plant. Proper storage is necessary when thinning crowded beds, relocating plants, or protecting them from harsh winter conditions. They require specific preparation and environmental control to remain viable during dormancy. Successful preservation hinges on minimizing the risk of rot and desiccation until the rhizomes can be safely replanted.
Preparing Rhizomes for Storage
The ideal time to lift iris rhizomes is in the late summer or early fall, typically six to eight weeks after the plant has finished blooming. This timing allows the rhizomes to fully mature and store sufficient nutrients for the next growing cycle. After digging them up, gently remove the bulk of the soil clinging to the rhizomes without washing them, as excess moisture encourages fungal growth.
Trim the fan of foliage back to a manageable “fan” shape, usually about 4 to 6 inches tall. Shorten any long, fibrous roots to approximately 3 inches. This trimming helps redirect energy to the rhizome and makes the units easier to handle.
The most crucial step is curing, where the prepared rhizomes are spread in a single layer on a flat surface in a warm, shaded, and well-ventilated area. Curing for several days to a week allows the cut surfaces to callous over. This forms a protective barrier that seals in moisture and prevents the entry of rot-causing pathogens during storage.
Selecting Storage Mediums and Containers
The choice of storage container and medium must balance air circulation with moisture control to prevent both rot and excessive drying. Breathable containers are necessary to allow for the free exchange of air. Suitable containers include cardboard boxes, wooden crates, or mesh bags. Avoid using airtight plastic bags or sealed containers, which trap moisture and create a humid environment conducive to mold and bacterial soft rot.
A dry storage medium can be used around the rhizomes if you need a slightly buffered environment, though this is not always necessary. Suitable materials include dry peat moss, sawdust, shredded newspaper, or vermiculite, which help absorb minor fluctuations in moisture. Place the rhizomes in the container in a single layer, or separate layers with crumpled newspaper, to ensure air circulates freely around each piece. Wrapping individual rhizomes in newspaper is also an effective technique for absorbing excess surface moisture and preventing contact between pieces.
Maintaining the Storage Environment
Successful long-term storage depends on maintaining a cool, dark, and dry environment with consistent temperature and humidity levels. The ideal temperature range for iris rhizome storage is between 40°F and 50°F (4°C and 10°C). This range keeps the rhizomes dormant without freezing; temperatures below 35°F can cause damage, while those above 50°F can lead to dehydration or premature sprouting.
A dry environment is preferred, as high humidity promotes the growth of fungi and bacteria that cause rot. Suitable locations include unheated basements, cool cellars, or garages that maintain temperatures above freezing throughout the winter.
Check the stored rhizomes periodically, perhaps once a month, for any signs of deterioration. Any rhizomes that feel soft, mushy, or show visible signs of mold should be immediately removed and discarded. This prevents the infection from spreading to healthy stock.