Flower bulbs are underground storage organs designed for survival and reproduction. The short answer is yes, flower bulbs naturally multiply over time, creating genetically identical copies of the parent plant. This multiplication allows a single bulb planted today to become a dense cluster of flowering plants within a few years, dramatically increasing the color and density in a garden bed.
The Biological Process of Bulb Increase
True bulbs, such as tulips, daffodils, and hyacinths, reproduce asexually, creating clones of the original structure. These bulbs are modified leaves surrounding a central stem, storing starches and nutrients for growth and survival during dormancy. New, miniature bulbs called “offsets” or “bulblets” form laterally at the base of the main, or mother, bulb.
Offsets are attached to the parent bulb’s basal plate, sharing resources until they develop their own root systems. As the parent bulb matures and completes its annual cycle, these smaller bulblets grow larger. Each offset is a genetic copy capable of growing into a full-sized, flowering bulb once it reaches maturity.
How Different Underground Structures Multiply
Many garden plants are casually referred to as bulbs, but they grow from different underground structures that multiply uniquely. Corms, such as crocus and gladiolus, are solid, swollen stem bases rather than layered leaves. A corm multiplies by producing a new replacement corm on top of the old one as the growing season progresses.
The new corm is accompanied by several tiny structures called “cormels” that form around the base. The old, depleted corm shrivels and dies, leaving the new corm and the cormels to mature. Corms often increase faster than true bulbs, which can lead to rapid overcrowding.
Other structures have distinct multiplication strategies. Rhizomes, such as those in irises, are horizontal stems that grow along or beneath the soil surface. They spread by branching out, with new shoots and roots developing from nodes along their length. Tubers, like dahlias and certain begonias, are thickened underground stems that enlarge annually. New plants sprout from the “eyes,” or growing points, on the tuber’s surface, forming an expanding cluster over time.
Managing Overcrowding and Dividing Clumps
The natural tendency of these structures to multiply eventually leads to overcrowding, negatively affecting the display quality. A primary sign that intervention is needed is when an established clump produces lush foliage but the flowers are noticeably smaller or fewer. The dense underground population causes competition for water, nutrients, and space, reducing the energy available for blooming.
To remedy this, gardeners must divide the clumps after the foliage has naturally yellowed and died back. This timing is important because the plant has finished photosynthesizing and storing energy into the bulb for the next season. For most spring-blooming varieties, division occurs in late spring or early summer, while summer bloomers are divided in early fall.
The process involves carefully digging up the entire clump with a garden fork to minimize damage. The offsets or cormels are gently separated from the mother structure, either by hand or using a clean, sharp knife for tougher connections like rhizomes. Any soft, diseased, or shriveled structures should be discarded. The separated bulbs are then replanted immediately, giving them ample space—two to three times their width apart—to allow for vigorous growth. Smaller bulblets may take one to four years to mature enough to produce their first flower.