Grow large, tropical-looking cannas in your garden and enjoy their banana-shaped leaves with multicolored or patterned leaves and large yellow, orange or red flowers. Plant them in well-draining soil beds in full sun and keep their soil moist, because cannas need lots of water. In the fall, after the foliage dies, cut back canna plants and dig up their rhizomes to store in a cool location that is between 45 and 55 degrees F. Then, replant them after the last frost in the spring. Always take care of any problems as soon as possible to keep your cannas healthy and thriving so you can enjoy them year to year.
Kill canna leaf rollers, which are brown moths that damage cannas, in their larvae--caterpillar--stage, with Bacillus thuringiensis (Bt). Canna leaf rollers eat holes through or the top part of the leaves. Also, like their name implies, canna leaf rollers attach silk to the leaves and roll them like one would roll a cigar. Spray Bt directly on the leaves and in the center of the rolled leaves to kill canna leaf rollers. In addition, clean up all the canna debris in the fall to prevent caterpillars from making your planting bed their winter home.
Control Japanese beetles, which multiply as the beetles attract more of their kind with pheromones. Apply milky spore to the soil to kill their larvae and knock beetles into buckets of soapy water to kill them. Do not destroy all beetles if you have problems with aphids.
Remove and throw out diseased plants to prevent the disease from spreading to other areas of your garden. Diseases common to cannas are canna mosaic virus, bud rot and aster yellows. Yellow lines, wrinkles, browning, and yellow spots are all signs that your cannas have been infected by a disease. Aphids spread these diseases, so control the aphids as well.
Control aphids, which are small, pear-shaped bugs that spread disease. Spray an insecticidal soap on the leaves or wash them off with a hose. Avoid using pesticides, if possible, because pesticides will also kill aphids' natural predators, such as beetles.
Stake cannas if they begin to bend over from being top-heavy. Insert a stake next to the base of the plant and loosely tie the canna to the stake with twine.