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Jane's Garden 6/29/14: Showy cannas are a perennial garden favorite

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Cannas are tall perennial exotic flowers suitable for most temperate and sub-tropical gardens in Florida. There are about 25 species in the genus, most originally from warm South America. None evolved in Asia. One wetland species, Canna flaccida, commonly named Yellow Canna, is native to Florida and ranges north to North Carolina in cold zones 8 to 10.

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Yellow Canna is a tall perennial (but deciduous in winter) that grows from a robust, knotty underground rhizome similar to gingers and bananas. It is prevalent in wet roadside ditches, shallow ponds and marshes. It needs regular irrigation and moist, humus-rich soil in a cultivated garden.

The “stem” is actually a bundle of tightly rolled leaf bases. Large, lance-shaped leaves spiral from the stem in an alternate pattern. Leaves are about 6 inches wide and 24 inches long, dark green with a lighter midrib.

A slender flower stem grows up through the furled leaf-base stem. Flowers have three bright, lemon-yellow petals about 3 inches long, with three modified yellow stamens that look like petals with ruffled edges. At the back are three greenish-yellow sepals. Four to six showy flowers top each flower stem. Cut these stems back before seeds start to form for a tidy look. Dark brown seeds are three-parted, held in a rough, round capsule about 2 inches in diameter.

The other wild exotic cannas have asymetrical, narrow-petaled flowers in red, yellow or purple. All garden Cannas are man-made hybrids and cloned cultivars with much broader petals. Canna crossbreeding began in the mid-1800s. Early hybrids had smooth petals in solid colors. When breeders introduced genes of C flaccida, the flowers turned out larger, ruffled and crumpled with many striking color variegations.

Colors of modern Canna hybrids range from solid red, white, yellow, peach, pink or orange to cream. Some plants have spotted, flecked and blotched darker markings on solid background colors. Depending on the variety, leaves can be green, bronze, purple or striped with lighter variegations. Dividing the rhizomes while dormant and leafless in winter makes many smaller plants identical to the parent. Allow each plant to grow into a wide clump for several years before dividing.

Cannas flower best in full sun and need humus-rich soil that retains moisture. Blanket the soil over the rhizomes with a few inches of natural, organic mulch like pine needles or oak leaves to protect them from hard freezes. Deep mulch prevents wind-blown weed seeds from reaching the soil and excludes light, so weed runners are deterred from sprouting. It also looks attractive and shades soil to reduce temperature in summer.

Cannas can be grown in large pots and placed at the edges of water features like ponds and waterfalls. The potted plants add color and provide cover and protection for visiting wildlife. C. flaccida can be planted in a bog or rain garden with its roots in the muck. The rhizome should be above the waterline to prevent rotting; therefore, the pot can be partly submerged on a plant shelf or shallow ledge.

Cannas flower for about six weeks in summer. They are readily available from retail nurseries and native plant growers.

Jane Weber is a professional gardener and consultant. Semi-retired, she grows thousands of native plants. Visitors are welcome to her Dunnellon, Marion County, garden. For an appointment, call 352-249-6899 or contact JWeber12385@gmail.com.