Gladioli are popular summer flowers, known for their dramatic, towering flower spikes. While commonly referred to as bulbs, a gladiolus actually grows from a corm, which is a swollen, underground stem base that acts as a food storage unit. Gladiolus multiplication is the plant’s natural reproductive strategy.
Understanding Corms and Cormels
The multiplication process begins with the corm structure. During the growing season, the original “parent corm” is consumed by the developing plant, shriveling as its stored energy is used to produce foliage and the flower spike. A new, larger “daughter corm” forms on top of the spent parent corm. This annual replacement ensures a fresh, mature corm capable of flowering the following season.
The primary mechanism for rapid multiplication involves small, hard offsets called cormels (or cormlets) that form around the base of the new daughter corm. These miniature structures are the plant’s asexual reproductive units. A single mature corm can produce a large quantity of cormels, sometimes ranging from a few to over a hundred, depending on the variety and growing conditions. Since cormels are genetically identical to the parent plant, they allow gardeners to expand their stock of a favorite variety.
Dividing Gladiolus Clumps
To manage natural multiplication and prevent overcrowding, corms and cormels should be separated annually or every few years. Division is best performed in late summer or autumn, four to six weeks after flowering, or when the foliage begins to yellow and die back. Use a garden fork to carefully lift the entire clump from the soil, avoiding damage to the corms. After lifting, cut the foliage back to within one or two inches of the corm top.
The next step is to “cure” or dry the corms by placing them in a warm, dry, well-ventilated location, out of direct sunlight, for about two to three weeks. This curing process helps the corm skin harden and seals minor wounds, preventing rot during storage. Once cured, the old, shriveled parent corm can be easily twisted off and discarded from the base of the new daughter corm. At this time, the small cormels formed around the base of the new corm should also be gently detached.
The separated daughter corms are the main flowering units for the next season. They should be stored in a cool, dark, and frost-free location, ideally between 35°F and 45°F (2°C to 7°C). Use breathable containers, such as mesh bags or open trays, to ensure good air circulation throughout the winter. Proper storage keeps the corms dormant and healthy until they are replanted the following spring.
Nurturing Cormels into Flowering Plants
While daughter corms bloom the following year, cormels require maturation before producing a flower spike. These tiny offsets create a stock of new, vigorous planting material. Cormels generally require between one and three full seasons of growth before reaching the minimum size necessary to bloom. Selecting the largest cormels, often around a half-inch in diameter, provides the quickest path to flowering.
Cormels should be planted in the spring, but their method differs slightly from mature corms to maximize growth. They are typically planted shallowly, about one-and-a-half to two inches deep, and spaced closely together in a dedicated nursery bed. This dense planting is acceptable because the goal is foliage production and corm enlargement, not an immediate floral display. During the first year, the cormels produce thin, grass-like foliage focused on building size.
At the end of the season, these newly enlarged corms must be dug up and stored for the winter, just like mature ones. This cycle of growing and storing is repeated until the corms reach a diameter large enough, generally over 1.5 inches, to reliably send up a flower spike.