A corm is a solid underground stem base that functions as a storage organ for plants. This modified stem stores starches and nutrients, allowing the plant to survive adverse conditions like winter dormancy. Species such as Gladiolus, Crocus, and many tropical varieties like Alocasia form corms, which must be lifted and stored when grown in regions where the soil freezes. Overwintering these tender corms protects them from cold temperatures and excessive moisture, ensuring the energy reserves are preserved for the following season’s growth.
Preparing Corms for Dormancy
Timing the harvest correctly is the first step in successful corm storage, typically occurring after the foliage naturally dies back or after the first light frost has wilted the leaves. Waiting until the plant has entered dormancy allows it to transfer the maximum amount of energy and nutrients back into the storage organ. Carefully dig around the plant with a garden fork or spade to avoid puncturing the corm, then gently lift it from the soil.
The initial drying process should take place immediately after lifting, with corms left in a protected, dry location for a few days to allow excess surface moisture to evaporate. This step is followed by cleaning, where you gently brush off any remaining soil and trim away the dead roots, old corm material, and spent foliage. Some gardeners find it easier to remove the old, shriveled corm base after a few days of drying, as it separates more easily from the new corm that formed above it.
Curing is a necessary step to harden the corm’s outer skin, which seals any minor wounds and prevents the entry of rot-causing pathogens during storage. This process involves laying the cleaned corms in a single layer in a warm, dry, and well-ventilated area, away from direct sunlight, for a period ranging from one to three weeks. For example, Gladiolus corms often benefit from a two- to three-week curing period to ensure a solid, dry surface before being moved to cold storage. A properly cured corm feels firm and dry to the touch, indicating it is ready for long-term dormancy.
Creating the Ideal Storage Environment
The goal of the storage environment is to mimic the cool, dry conditions a corm would naturally experience during its rest period. Temperature control is important, with an ideal range being cool but above freezing, generally between 35°F and 50°F. Temperatures near 40°F are often recommended for many common varieties like Gladiolus and Alocasia corms, as this range keeps them dormant without risking freezing damage.
Controlling humidity is equally important to prevent both shriveling and mold growth. The air should be relatively dry, ideally maintaining a relative humidity below 70%, which discourages the proliferation of fungal spores that cause rot. Poor ventilation and high moisture allow pathogens to thrive, which can quickly ruin stored corms.
Corms must be stored in containers that allow for adequate air circulation, such as mesh bags, paper sacks, or cardboard boxes with ventilation holes cut into the sides. Never use sealed plastic bags or non-ventilated containers, as they trap moisture and inhibit airflow. The cured corms should be layered with a dry, inert medium, ensuring they do not touch one another.
This medium absorbs residual moisture and provides a small buffer against temperature fluctuations. Suitable mediums include:
- Peat moss.
- Vermiculite.
- Sawdust.
- Shredded newspaper.
Monitoring and Troubleshooting Stored Corms
Regular monitoring is necessary throughout the winter months to prevent storage failures. Check on the stored corms at least once a month, visually inspecting them and gently feeling the texture of the outer skin. The first signs of trouble are often visible as patches of white or green mold, which indicate the storage environment is too humid or lacks sufficient air movement.
If mold or rot is discovered, immediately remove the infected corm entirely and discard it away from the rest of the stored batch. Rot is identified by soft, mushy, or discolored areas on the corm, signifying that the internal tissues are breaking down. If a significant number of corms show signs of mold, the entire storage medium should be replaced, and the containers should be moved to a drier location.
If corms begin to shrivel severely, it suggests the storage area is too dry, causing them to lose too much internal moisture. A light misting of the surrounding storage medium, without directly wetting the corms themselves, can introduce a small amount of humidity to correct this issue. Conversely, if the medium feels damp, spread the corms out to air dry for a day or two before re-packing them in fresh, dry material.