Cannas (Canna) are a genus of beautiful, easy-to-grow plants with showy flowers that come in red, pink, yellow, orange, and cream. Canna leaves are wide and long (resembling banana leaves) in green, bronze, or multicolored patterns. Most cannas grow up to 6 feet tall and occasionally as tall as 8 feet. These plants grow from rhizomes, underground stems that send up plant shoots. Best planted from rhizomes in the early spring, cannas can take a few weeks to sprout. But then they grow at a fairly quick pace and typically flower in their first year.
|Common Names||Canna, canna lily|
|Plant Type||Flowering perennial|
|Mature Size||1.5 to 8 feet tall and 1.5 to 6 feet in spread|
|Sun Exposure||Full sun|
|Soil Type||Rich, moist, well-draining|
|Soil pH||6.5 (but tolerates a wide range)|
|Flower Color||Red, orange, yellow, pink, cream|
|Hardiness Zones||7 to 10|
|Native Areas||South America, Central America, West Indies, Mexico, Southeastern United States|
How to Grow Cannas
In the garden, plant canna rhizomes horizontally 5 inches deep, and cover them with a thick layer of mulch. Leave about 2 feet of space around the rhizomes. These plants don't like to be crowded, and if other plants encroach they might refuse to bloom.
After the first frost of the fall, cut the canna back to the ground, and carefully dig up the rhizome clumps. Store them for the winter in peat or vermiculite in a spot that doesn't fall below 40 degrees Fahrenheit. (You can simply bring container plants indoors in their pots.) Spray the rhizomes with water infrequently to prevent them from drying out, but don't allow them to sit in a consistently damp medium.
These plants prefer full sun to grow vibrant leaves and flowers, but they can survive in a little shade. Just make sure to monitor that the soil doesn't get overly moist due to the shade.
Cannas can tolerate a variety of soils as long as there is good 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 alkaline soils.
Plan to water your canna once or twice a week. The soil should be kept uniformly moist but not soggy. Otherwise, this can lead to rot in the plant.
Temperature and Humidity
Cannas are sensitive to cold temperatures and frost, but they thrive in temperatures up to 90 degrees Fahrenheit.
These plants are native to tropical zones, so they also do well in humid conditions. If you live in a dry climate, you can raise humidity around a container plant by placing it on a dish filled with water and pebbles, making sure the bottom of the pot isn't touching the water.
Cannas are heavy feeders. So use plenty of compost or organic fertilizer to keep the plant happy. As long as you use organic materials, you cannot overfertilize a canna. Feed monthly throughout the growing season, starting in the early spring, with a balanced fertilizer.
Growing Cannas in Containers
Cannas are large plants, so bigger is better in terms of choosing planting containers. Choose a pot that is between 15 and 18 inches in diameter. This is not only for aesthetic reasons. It also gives the plant space to grow strong and healthy, and it prevents the pot from tipping over.
Cannas can be propagated from seeds, but the more common method is to lift and divide the rhizomes. Fall or early spring are the best times to divide cannas.
To do so, dig up the entire mass of rhizomes, and cut off the stems to about 1 inch. Brush off the soil to expose the joints where new rhizomes sprout off the old rhizomes. Use a sharp knife to slice the rhizome segments apart. Each section should have at least one eye (the bump along the top of the rhizome that sprouts a new plant). Replant the pieces about 5 inches deep.
Common Pests and Diseases
Slugs, snails, and Japanese beetles delight in chewing holes in the leaves and flowers of cannas. 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 then 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 using a mild insecticide on the plant.
Cannas also are susceptible to rust fungus, canna mosaic virus, and aster yellows. Watch out for foliage that appears sickly and discolored. With rust fungus, you often can simply remove the affected leaves. But with canna mosaic virus and aster yellows you often have to remove the entire plant.
Varieties of Cannas
There are hundreds of varieties of cannas, ranging in color and size. Some popular varieties include:
- 'King Humbert': This variety originated in 1902 and has dark bronze-purple foliage and red flowers.
- 'Shenandoah': This plant bears deep pink flowers with burgundy leaves.
- 'Tropicana': This a newer variety with orange flowers that grow above the leaves, which are striped with burgundy, gold, yellow, pink, and green.