Cannas are tropical and subtropical perennials with showy flowers and large green, bronze, burgundy and multicolored banana-shaped leaves. Flowers are large with recurved, multilayered petals of yellow, orange, pink and red. Most canna varieties grow to a height of 3-5 feet. However, there are dwarf varieties that measure 18 to 24 inches high.
Cannas are relatively easy to grow at all elevations in Southern Arizona. Shoots emerge in the spring from rhizomes (thickened underground stems). Blossoms are produced on tops of clumping upright stems. Flowering continues until the tops die back to the ground with the first freezing temperatures of fall. At that time, the stems can be cut back to the ground. At elevations up to 4,000 feet, underground rhizomes can be left in the ground to re-sprout the following spring. At higher elevations, such as Mount Lemmon, rhizomes must be dug up and stored during the winter months, then replanted in spring after the danger of frost has past.
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Regardless of the growing location, put a mulch covering over your cannas after pruning them off in the fall. The mulch can be a thick (4 to 6 inch deep) layer of compost, pine needles, ground wood mulch, forest mulch or straw. This mulch layer will keep the soil and the canna rhizomes slightly warmer over the winter.
When planting cannas, mix lots of organic matter into the planting soil. I prefer to use either bagged compost or manure. Most bagged top soils are also high in organic matter. Work your organic amendment into the top 12 inches of soil.
Plant canna rhizomes in early spring a few weeks before the average frost free date in your area. Plant them 4 inches deep and 1 to 2 feet apart, depending on the ultimate size of the cultivar(s) you've selected. Potted canna plants are often available at garden centers and home-supply stores and may be planted from spring to fall.
Cannas perform best in moist soils in full sun or partial shade. They also tolerate poorly drained soils. Water frequently enough to keep the soil evenly moist. To conserve moisture, mulch the soil with compost, ground wood or wood chips. To promote growth, fertilize in spring and mid-summer with a balanced garden fertilizer, such as a 10-10-10.
Remove spent flowers to maintain their attractive appearance and promote additional blooms. A new flower shoot will develop, or may already be developing, at the leaf node (where the leaf is attached to the stem) below the spent flower. When this secondary bloom flowers and finally fades, cut it off, and yet another flower will develop.
To keep your cannas looking and flowering their best, every two or three years, dig, divide and select healthy rhizomes for replanting. As cannas grow, new rhizomes develop underground. These new rhizomes should be selected for replanting and the older rhizomes discarded.
Spade up and divide each clump in the spring prior to new shoot development. Discard those that are old and do not contain buds (eyes) that will develop into new shoots. The rhizomes that have been selected for replanting should be cleaned. Rinse the soil off with water and then follow by rinsing them with a bleach solution made by mixing one part bleach with nine parts water. Let them dry for a few days prior to planting. After planting, water to keep the soil evenly moist.