Finding a corm signals the potential for a new plant, as this small structure holds the key to propagating many popular houseplants and garden favorites. This guide explains what a corm is and how to successfully grow a new plant from it.
What Are Plant Corms?
A corm is a specialized, swollen underground stem base that functions as a storage organ for plants. Unlike a true bulb, which is made of fleshy, layered leaves, a corm is solid, storing starches and nutrients within its stem tissue. These structures appear rounded or flattened, often encased in a papery, protective tunic. Corms enable plants to survive periods of dormancy, such as cold winters or dry seasons, by holding energy reserves.
They also facilitate asexual reproduction, allowing new plants to grow as exact genetic copies of the parent. Many houseplants and garden varieties produce corms. Examples include Alocasias and Colocasias, often called Elephant Ears, known for their dramatic foliage. Gladiolus and Crocus also grow from corms, producing vibrant flowers. Oxalis, or the purple shamrock, also develops from corms, sometimes described as pinecone-shaped.
Harvesting and Preparing Your Corm
Corms are discovered during repotting or when a plant enters dormancy. When unpotting, feel through the root ball and soil for small, firm, rounded structures. These corms might be loose or still attached to the mother plant’s root system. If attached, use clean, sharp snips to cut the corm from the main plant, making the cut as close to the corm’s base as possible without damage.
Once separated, clean the corms by removing any clinging soil and old, withered roots or leaves. Some corms have a brown, papery outer shell, similar to a peanut shell, which can be peeled away to encourage faster sprouting. If the shell is stubborn, soaking the corm in room-temperature water for 30 minutes can help soften it for easier removal. After cleaning, allow the corms to air dry a few days in a well-ventilated area to help the cut surfaces callous over, reducing the risk of rot before planting.
Planting and Growing Your Corm
Corm propagation requires a well-draining and airy potting medium. A mix of sphagnum moss, perlite, or coco coir works well. For planting, select a small pot, 3-4 inches in diameter, ensuring it has drainage holes to prevent waterlogging. Position the corm with the slightly more pointed end facing upwards, as this is where new growth will emerge; if uncertain, laying it on its side is also acceptable.
Plant the corm just below the surface of the medium, or with the top partially exposed. After planting, water to moisten the medium thoroughly. Maintain moisture, keeping the medium damp but never soggy, to encourage root development and sprouting. Provide bright, indirect light and a warm environment, ideally above 65°F (18°C), and aim for high humidity, which can be achieved by covering the pot with a clear plastic bag or humidity dome. Corms can take anywhere from a week to several months to sprout, with many showing growth within 2-4 weeks.
Common Corm Challenges
Corms can present challenges during propagation. One issue is a corm failing to sprout. This can occur if the corm is non-viable, if conditions are not consistently warm and humid, or if the corm is taking a prolonged period of dormancy. Maintaining stable temperatures and humidity levels can encourage reluctant corms to emerge.
Rotting corms are another problem, caused by overwatering, insufficient drainage, or fungal issues. Ensure the potting medium is well-aerated and never waterlogged. If a corm feels soft or mushy, it is rotting and may not recover. Addressing mold, which can appear, involves improving airflow and ensuring proper moisture balance.
Slow growth or stalling can also happen due to insufficient light, low temperatures, or a lack of nutrients in the propagation medium. Providing adequate light and warmth, along with appropriate humidity, supports robust development once the corm begins to grow.