Cannas are striking, ornamental plants prized for their vibrant, tropical foliage and showy blooms. These robust garden additions are grown from a specialized underground storage structure. Understanding the physical characteristics and biology of this subterranean organ is important for successful cultivation. This article describes the appearance and features of the Canna lily’s underground unit.
Understanding the Canna Structure
Although many people refer to Canna lilies as having “bulbs,” the correct botanical term for their underground structure is a rhizome. Unlike a true bulb (like a tulip), which is a modified leaf structure, the Canna’s rhizome is a modified horizontal stem that grows beneath the soil surface. This structure is primarily responsible for storing starches and proteins, fueling the plant’s growth and survival through dormant periods. It allows the plant to sprout new shoots and roots from various points along its length.
Detailed Physical Appearance
A dormant Canna rhizome is typically irregular in shape, appearing knobby, elongated, and often multi-branched, similar to a piece of ginger root. It bears little resemblance to the neat, rounded form of a true bulb. Size varies significantly by cultivar, ranging from small, finger-like pieces to large, hand-sized masses. Robust, chunky rhizomes are preferred for vigorous growth, though some aquatic varieties may have thinner structures.
The exterior skin of the rhizome is generally rough and papery, colored tan, beige, or light brown. The surface is often segmented, showing distinct divisions. If cut open, the interior flesh is usually pale yellow or creamy white and has a starchy texture, confirming its role in food storage. This dense, lumpy appearance is a key identifier when selecting planting material.
Identifying Growth Nodes
The most important physical feature on a Canna rhizome is the presence of growth nodes, commonly called “eyes.” These nodes are small, pointed bumps located along the segments and curves of the rhizome. They are the specific points from which new shoots and roots will emerge. A single, well-developed rhizome division should possess at least two or three viable eyes to ensure successful sprouting.
The appearance of these nodes can indicate their readiness for growth. While the main body of the rhizome is tan, the growing tips of the eyes may appear slightly paler, often light pink or white. The number of eyes is directly related to the plant’s potential size and the abundance of its blooms. When planting, positioning the rhizome with the eyes facing upward or sideways encourages the quickest emergence of new stems.
Assessing Rhizome Health
The viability of a Canna rhizome can be determined by a simple visual and tactile inspection. A healthy rhizome should feel heavy, firm, and plump, indicating high starch and moisture content. The skin must be intact, and the growth nodes should appear undamaged and distinct, with no sign of shriveling. The absence of any strong, sour, or foul odor is also a positive sign of health.
Conversely, signs of poor health or decay should be avoided. A rhizome that feels soft, mushy, or slimy when squeezed is likely rotting, often due to fungal infection from excess moisture. Dark spots, discoloration, or a grayish hue on the exterior suggest rot or disease. A rhizome that feels brittle and lightweight may have desiccated in storage and is unlikely to sprout.