Throughout their hardiness zone, cannas can remain in the ground as true perennials. In colder climates, the rhizomes must be dug in the fall and stored over the winter, then replanted in the spring. Best planted from rhizomes in the early spring, cannas can take a few weeks to sprout. After sprouting, they grow at a fairly quick pace and typically flower in their first year. Canna leaves have a waxy coating that helps resist fungal diseases. They are also generally resistant to pest problems, although you might find caterpillars or grasshoppers eating the leaves—remove them by hand.
Light
These plants prefer full sun to grow vibrant leaves and flowers, but they can survive in partial sun.
Soil
Cannas can tolerate a variety of soils with proper drainage. They prefer rich soils that are high in organic matter. A soil pH of roughly 6.5 is ideal, but cannas can handle a wide range of acidic to neutral soils.
Water
Water your canna once or twice a week. The soil should be kept uniformly moist but not soggy. Overly wet soil can lead to rot.
Temperature and Humidity
Cannas are sensitive to cold temperatures and frost, but they thrive in temperatures up to 90 degrees Fahrenheit. In areas that have relatively cool springtime temperatures, canna growth might start slowly. In cooler climates, USDA cold hardiness zones 7 and lower, you can get a head start on the growing season by starting them indoors in pots and then move them outdoors once they are actively growing and all danger of frost has passed. These plants are native to tropical zones, so they do well in warm and humid conditions. If you live in a dry climate, you can raise the humidity around a container-grown plant by placing it on a dish filled with water and pebbles, making sure the bottom of the pot isn’t touching the water.
Fertilizer
Cannas are heavy feeders. Feed them monthly, or at least twice during the growing season, once in early spring, and again in mid-summer, with a fertilizer that is high in phosphorus, such as 5-10-5, to encourage blooming. You can also use plenty of compost or organic fertilizer to provide the plants with extra nutrients.
Types of Canna
Hundreds of canna cultivars are available in a wide range of foliage and bloom colors and mature size. Some popular varieties include:
‘Red King Humbert’ or ‘Yellow King Humbert’: at over a century old, these are two of the oldest cultivars. ‘Red King Humbert’ grows up to eight feet tall and produces large red to reddish-orange blooms. ‘Yellow King Humbert’ grows four to five feet tall and produces bi-color golden yellow blooms with splashes of orange. ‘Shenandoah’: bears deep pink flowers with olive green leaves that have a touch of bronze’Tropicanna’: produces orange flowers with leaves striped with burgundy, gold, yellow, pink, and green’Pretoria’ (‘Bengal Tiger’): produces bicolored orange flowers with yellow and green striped foliage’The President’: grows up to five feet tall and produces very large scarlet flowers that provide a striking contrast with its deep green foliage’Stuttgart’: produces orange flowers and is distinguished by its bold striped green-and-white foliage. It grows best in partial sun because full sun could scorch its leaves.
Pruning
Cannas generally do not need pruning, but deadheading the flower stalks (once the flowers have faded) will produce more blooms. If you prize the foliage of your cannas over their flowers, you can cut off the flower stalks before they bloom to enable the plants to direct their energy toward the foliage.
Propagating Cannas
Cannas are readily propagated by digging up the rhizomes and dividing them for replanting. Do this early in the spring or in the fall.
Potting and Repotting Cannas
Cannas are large plants, so bigger is better in terms of choosing an appropriate container size. Choose a container that is no smaller than 16 inches in diameter with adequate drainage holes. A large container is not only important for aesthetic reasons of scale but it gives the plant space to grow a strong and healthy root system. A large container reduces the chance of the plant becoming top heavy and tipping over as it matures. Make sure the container has good drainage, and fill it with quality potting soil. Because cannas are heavy feeders, mix some slow-release fertilizer into your potting soil before planting. If you live in a cold-winter climate and have saved rhizomes from last year’s plants, you can get a head start on the next growing season by potting up the rhizomes indoors four to six weeks before the last frost in spring. Maintain adequate moisture but do not make the soil overly wet. Move the pots outdoors or plant them in the ground after the danger of frost has passed.
Overwintering
In colder climates, after the first frost in fall, cut down the canna to the ground. Carefully dig up the rhizome clumps and store them through the winter in dry peat moss, coconut coir, or vermiculite in a location where the temperature does not drop below 40 degrees Fahrenheit. Spray the rhizomes with water once in a while to prevent them from drying out, but don’t allow the rhizomes to sit in a consistently damp medium. You can bring container-grown plants indoors for the winter.
Common Pests & Plant Diseases
Slugs, snails, and Japanese beetles delight in chewing holes in canna leaves and flowers. But the worst pest is a caterpillar known as the canna leaf roller. The canna leaf roller moth lays its eggs in the bud of a growing stalk, and the hatching caterpillars leave a sticky webbing that prevents the leaf from unfurling. Remove a leaf if you see that it’s unable to unfurl, and consider spraying the plant with insecticidal soap if pests are present Cannas can have several other problems. They are susceptible to rust fungus, canna mosaic virus, and aster yellows. Observe foliage that appears sickly and discolored. With rust fungus, you often can simply remove the affected leaves. But if the plant is infect with canna mosaic virus and aster yellows, you should dispose of the entire plant.
