Canna Bulb Care

Canna blossoms and the rounded seed pods.

Known for its vividly colored flowers, large bananalike leaves, and love of warmth and soil moisture, canna is a tropical perennial grown in frost-free months. While people refer to it as a bulb, it is, more accurately, a tuber--a fleshy horizontal stem that stores food and remains underground. In U.S. Department of Agriculture Plant Hardiness Zones 8 and warmer (higher), you can leave these tubers in the ground over winter.

Planting

Canna tubers are best planted in fertile soil that is rich in organic matter like compost or well-rotted manure. The soil's texture should be loose and crumbly when dug. Plant the tubers at a depth of 5 inches, laying them horizontally with any sprouting eyes pointed upward. Space tubers at least 10 inches apart if you are planting them in a furrow row or multiple planting holes. In USDA Plant Hardiness Zones 3 through 6, where winters are too cold for them to survive outdoors, consider planting them indoors in pots with bottom heat in early spring to get them to sprout early, then transplant them outdoors once danger of frost passes, as recommended by Brent Heath of a bulb retail company in Virginia.

Moisture

While the canna tuber will sprout and grow in average garden soil conditions, these plants appreciate and respond with lusher growth when warm soils are damp to saturated/soggy. During the growing season, ensure the tubers are well watered so they can grow healthfully and receive nourishment from all of the above-ground foliage. In winter months, either in the ground or when stored indoors, they should remain in a moist medium, not as wet as during the warmth of summer.

Overwintering

In USDA Pant Hardiness Zones 7 and warmer, allow the tubers to remain in the soil in the garden to overwinter. The light frosts and freezes will not harm the tubers in the ground. Consider keeping the foliage on the plants over the winter, as it can act as an insulator for the tubers during particularly cold nights, shielding the ground. In chilly winters or to be proactively safe in zones 7 and 8, feel free to mulch the soil over the tubers to help insulate them from cold. In zones 6 and colder, allow the first fall frost to kill the above-ground foliage and flowers. Carefully dig up the tubers and cut off the leaf stems with a pruners, leaving about 1 to 2 inches of stem next to their attachment to the tuber. Allow any clinging soil to remain on tubers. Store them in a sturdy plastic bin or a large plastic garbage bag that is left loosely open. Place the tubers in a dark place where the temperature is between 45 and 55 degrees F, such as in the basement or in a cool, frost-free part of the garage. Occasionally check on the moisture across the winter and spray the soil with water to keep the soil moist, neither crusty dry nor soggy wet. Cannas grown in containers can simply be brought indoors and placed in a sunny window to overwinter. Water them lightly to keep soil barely moist while in the house.

Division

At some point the tubers will become large or create a branching matrix of side tubers. When the clump is dug up after the fall frost or when you wish to lift and divide the clump in the garden location, examine the tubers. With a sharp knife you can cut off side tubers that have eye sprouts, to replant. Cut away and destroy any tuber parts that are rotten, are soft, smell of sulfur or look shriveled and unhealthy. Some tubers become infected with viruses after growing in the garden. Spray your cutting blades with rubbing alcohol to disinfect them and prevent the spread of any viruses or other pathogens among the tubers during division.

Spring Care

Canna tubers do not survive well in cold, wet soils. In USDA Plant Hardiness Zones 7 and warmer--where canna tubers can overwinter in the ground--some spring tasks are warranted. In mid-spring when the intensity of the sunlight is more evident, prune away any lingering dead-leaf stalks from the canna plants. Pull back any winter mulch placed over the area to allow the sun to warm the soil. New growth emerges more quickly when sun and soil heat is evident. If you overwintered plants in containers in the house in colder climates, transplant them outdoors only after danger of frost has passed. Lightly fertilize plants only when temperatures consistently get above 75 degrees F daily.

References

• "Brent and Becky's Bulbs Summer-Flowering Bulbs Catalogue"; Brent Heath; 2009
• Karchesky Canna Collection: Tips for Growing Cannas and Other Tender Perennials
• Easy-to-Grow-Bulbs: Canna Lily Growing Information
• "Sunset National Garden Book"; Kathleen N. Brenzel, ed.; 1997
• "A-Z Encyclopedia of Garden Plants"; Christopher Brickell and H. Marc Cathey, eds.; 2004