What Is Plant Hardiness for Cannas?
The plant familiarly known as the canna lily (Canna x generalis) is a hybrid species of sub-tropical flower prized for its large, showy flowers and leafy, banana-like foliage. Widely grown during Victorian times, the plant has recently regained popularity; its ease of care and showy growth habit has made it a favorite not only in home gardens but as a choice for growing along roadsides and in highway medians. Cannas survive outdoors in the winter in southern climates, but require additional care to be grown in northern gardens.
The huge selection of cannas sold in today’s marketplace are hybrid species of one or more species of canna. The main parent is a plant native to the Caribbean, Indian shot (Canna indica), which now grows widely around the world. Over 100 separate named cultivars exist; as such, hybrid cannas vary widely in their size and color; some types are as short as 2 feet, though many can grow to 5 feet or more. Foliage color ranges from grass green to purple to red, but leaves on all canna plants have a characteristic banana-leaf shape. By far the most recognizable feature of the canna plant are its flowers, which are showy and long-blooming. Flower color runs the spectrum, but the most common hues are yellow, orange and red.
Care and Culture
As tropical-type plants, cannas grow best in rich but slightly sandy, moist but well-drained soils. Plants will tolerate partial shade conditions at the expense of flower display; in full sun, cannas will bloom continually until the first frost. Plants respond well to light, frequent feedings of fertilizers higher in phosphorous. Cannas are relatively pest-free, with no specific diseases or attacks by insects other than the garden-variety crop of pests found in all gardens, including aphids, thrips and mites. Rhizomes can be divided and replanted every few years.
Cannas are reliably hardy as far north as Zone 7, which includes New York’s Long Island, Virginia, the Delmarva peninsula, southern Tennessee, mid-state Missouri, southern Oklahoma and parts of the Texas panhandle, as well as patchy areas of the Sierra Nevadas and West Coast mountain ranges. While canna will grow and flower during the summer months as far north as Zone 4, gardeners in areas north of Zone 7 are advised to dig up the plant’s rhizomes and store them for the winter. In-ground overwintering is difficult when winter lows consistently drop below 0 degrees Fahrenheit.
Digging and Storing
The thick, fleshy rhizomous root of the canna is ready to be unearthed for the winter anytime after the first frost, which will kill and blacken the above-ground foliage. Stems should be trimmed back, leaving 2 or 3 inches of the stalk attached to the root, and left to dry. Once the rhizome has air-dried for a day or two, store the roots in a cool, dark area indoors, such as in a basement or cellar. Storing the roots in a box with sawdust or dry peat moss will help keep the rhizomes free of moisture that could lead to rot.
In northern climates where roots must be brought indoors for the winter, plants should be set out once soil has warmed to at least 40 degrees F and all danger of frost is past. Gardeners in zones 10 and 11 can set plants out as early as February; Zone 7 gardeners will have better luck with plantings timed for April or May. Begin fertilizing once the plant has completely broken dormancy and has unfurled several leaves.