Canna lilies are tropical, rhizomatous plants prized for their large, paddle-shaped foliage and brilliant, vibrant flowers. While many varieties feature solid green or bronze leaves, cultivars with striped or speckled patterns—known as variegation—are highly sought after by gardeners. Growing these patterned plants successfully requires understanding the biological mechanism that creates this unique aesthetic and providing the precise care needed for a variegated canna to thrive.
The Science Behind Variegation
The striking pattern on a variegated canna leaf is the result of a genetic event known as chimerism. A chimera is a single plant composed of two or more distinct genetic cell populations existing side-by-side. In variegated leaves, a mutation occurred in the plant’s meristem, or growth point, causing some cell layers to lose the ability to produce chlorophyll.
Chlorophyll is the green pigment responsible for photosynthesis; its absence in certain cell lines creates the white, yellow, or pale-colored streaks. These distinct cell lines divide and grow next to each other, forming the visible patterns. The location of the mutation within the apical cell layers determines whether the variegation appears as stripes along the leaf margin or as more random, sectoral blocks of color.
Variegated plants have a reduced capacity for converting sunlight into energy because the pale sections of the leaf contribute little to photosynthesis. This biological inefficiency is why caring for a patterned canna differs from caring for a standard, solid-green variety. The plant must work harder with less green tissue to sustain growth.
Cultivating Variegated Cannas
Due to their reduced photosynthetic ability, variegated cannas require significantly more intense light than their solid-green cousins. Providing a minimum of six to eight hours of bright, direct sunlight daily is necessary to encourage robust growth and retain the patterned foliage. Lower light levels, which standard cannas can tolerate, will cause a variegated plant to produce less-defined patterns or even revert to solid green.
Consistent moisture and nutrient delivery are crucial for these high-energy plants. Cannas thrive in consistently moist, well-draining soil and should never be allowed to dry out completely during the active growing season. Regular feeding with a balanced, liquid fertilizer is important, especially during the peak summer months. The ideal growing environment is consistently warm, with temperatures around 80°F promoting the fastest development.
Maintaining the Pattern
The major challenge in growing variegated cannas is the instability of the pattern, a phenomenon known as reversion. This occurs when the more genetically efficient, solid-green cells begin to grow faster and stronger than the less efficient variegated cells. If left unchecked, these solid-green sections, often called “sports,” will eventually take over the entire plant, causing the desirable pattern to disappear.
Gardeners must be vigilant in inspecting their plants for any stems or shoots that emerge as completely solid green. Once identified, these reverted shoots must be pruned away immediately, cutting them back to the point where they originated on the rhizome or stem. Failure to remove these aggressive green sections allows them to divert energy away from the patterned parts, leading to the complete loss of variegation. Managing fertilization is also important, as excessive nitrogen can stimulate the growth of these vigorous, green shoots.
Propagation and Division
To ensure the patterned leaves are passed on to a new plant, variegated cannas must be propagated asexually through rhizome division. Since the variegation is a somatic mutation, it is not reliably encoded in the plant’s seeds, and growing from seed will almost always result in a plain green plant. Division should be performed in early spring before new growth begins, or after the plant is lifted for winter storage.
The underground rhizomes should be carefully cut into sections, ensuring each piece contains at least one healthy growth node, or “eye”. For variegated cannas, the selected rhizome piece must originate from a section of the plant that exhibits the desired color pattern. Dividing a rhizome from a reverted, solid-green stalk will only yield a new, non-variegated plant, even if the parent plant still has patterned foliage.