Storing iris stock is a temporary measure, usually necessary when dividing crowded plants or preparing purchased stock for delayed planting. Irises are separated into two main types: those that grow from true bulbs (like Dutch and Siberian Irises) and those that grow from thick, modified stems called rhizomes (such as Bearded Irises). Although both are storage organs, their physical differences mean they have slightly different tolerances for remaining out of the soil. Proper handling prevents desiccation or rot before they can be established.
Maximum Storage Timelines for Iris Stock
The ideal scenario for any iris is immediate planting upon division or purchase to minimize stress and maximize root establishment. Bearded Iris rhizomes, which are fleshy stems designed to store moisture, are the most sensitive to prolonged storage. They should be planted within a short window, generally no more than two to four weeks, to ensure the best chance of survival and strong growth. Beyond this period, rhizomes risk significant dehydration and may not establish well.
True iris bulbs, including Dutch and Reticulata varieties, are slightly more forgiving and tolerate storage for a longer duration. If environmental conditions are perfectly maintained, these bulbs can sometimes be stored for up to six weeks, or even a few months. However, exceeding this time increases the risk of the bulb drying out and losing viability. The overall maximum storage limit for iris stock is typically one year, but this extreme duration requires commercial, climate-controlled conditions and is not practical for the home gardener.
Essential Conditions for Successful Storage
Controlling the storage environment is the most important factor in preserving the health of iris stock until planting time. A cool, dry environment is necessary to slow the plant’s metabolism and prevent the growth of fungal pathogens that cause rot. The optimal temperature range for storing most iris stock falls between 40°F and 50°F. Temperatures below 35°F can harm the internal structure, while excessive heat causes rapid drying.
Excellent air circulation is required, as stagnant air allows moisture to collect and encourages mold and fungus. Stock should be placed in shallow, single layers within breathable containers, such as cardboard boxes with ventilation holes, mesh bags, or open-weave plastic bins. To manage humidity, the stock can be nestled in a dry, inert medium like peat moss, wood shavings, or dry sand. Importantly, never use airtight plastic bags or sealed containers for storage, as these will trap moisture and quickly lead to rot.
Assessing Viability Before Planting
Before planting, a physical inspection is necessary to confirm the iris stock remains healthy and capable of growth. A healthy rhizome or bulb should feel firm and solid when gently squeezed, indicating adequate internal moisture reserves. If the stock feels soft, mushy, or squishy, it signals internal rot, often caused by excessive moisture during storage.
Visual signs of viability include the absence of moldy growth, slimy patches, or foul odors. A rhizome that has begun to shrivel and appears significantly dehydrated may still be planted, but its chances of flourishing will be reduced. Any stock that is soft, moldy, or has a distinctly unpleasant smell should be discarded immediately to prevent soil-borne pathogens from affecting new plantings.