Prized for their lush foliage and vibrant flowers, cannas (Canna spp.) add a tropical ambiance to perennial garden beds within U.S. Department of Agriculture plant hardiness zones 7 through 10. They bloom abundantly all summer, sending up their colorful, 4- to 6-inch-wide flowers in successive waves. Deadheading -- removing spent flowers and seed capsules -- faithfully throughout the blooming season helps to prolong blooming, and it may increase the number and quality of flowers.
Preparation for Success
Deadheading enhances cannas' appearance, but it can cause damage if the wrong tools are used or improperly prepared. A sturdy pair of bypass or scissor-type pruning shears should be used because their sharp, overlapping blades create clean cuts. The blades should be sharp and rust-free to prevent tearing of flower spikes. Before deadheading, soak the blades in a sanitizing solution, such as a full-strength household disinfectant or a mixture that is 50 percent rubbing alcohol and 50 percent water for five minutes. Then rinse them in hot water, and wipe them dry with a clean cloth.
The deadheading process differs by the type of plant. Cannas produce multiple flowers on a single spike, with each flower lasting several weeks. The individual flowers should be snipped off when they start to fade, and then each stalk can be cut off at its base after all the stalk's flowers have been removed. Deadheading prevents seed development. So if you hope to grow new cannas from seeds, leave one or two flowers and their stalks in place until autumn, and then gather the seeds from the seedpods, which are spherical, hairy capsules.
Cannas seldom suffer from serious disease or pest issues. Sometimes, however, they contract viral infections when deadheaded with tools that were tainted by infected cannas. Common infections include canna mosaic virus and aster yellows, which include symptoms such as yellowing and browning of foliage and stunted growth. Neither disease is curable, and both are highly contagious. Do not deadhead or prune cannas that have worrisome symptoms, especially with tools that are used on other canna plants. Instead, discard the infected plants immediately, and soak all pruning tools that have been used on them in a household disinfectant before using them again.
Advantages and Reasons
Deadheading benefits most plants, especially those such as cannas that have a lengthy and intensive bloom season. Removing old flowers redirects a plant's energy from seed production to producing more flowers. Another benefit of deadheading cannas is that it tidies their appearance. Cannas are dual-purpose plants because they have flowers and foliage that are equally ornamental. Keeping cannas' old flower spikes cut back allows the plants' foliage, which resembles banana plant foliage, to shine.