Cannas, also called canna lilies, are large--up to 6 feet tall--tropical-looking plants that are hardy in USDA Hardiness Zones 7 and warmer. They love moist soil, which makes them the perfect plant to grow near the water. They have underground root stems called rhizomes, which can be stored in colder areas to grow them year to year. Growing cannas in groups or along an edge of a water source will lend a tropical look to your water garden.
Choose a sunny spot near the water. Cannas will grow well in partial shade, but will bloom more profusely in areas that receive at least six hours of sunlight.
Wait until after the last spring frost to plant cannas. Cold, wet soil conditions, such as those near water sources, can cause canna rhizomes to rot.
Mix in 1 to 2 inches of rotted manure or compost into the top 6 inches of soil. This will create the ideal rich and moist soil conditions where cannas thrive.
Plant rhizomes 1 to 2 inches deep near the water where soil is moist. Plant them with the eyes facing upward. If rhizomes are large and have lots of eyes, cut the rhizomes into smaller pieces with a clean utility knife so each section has a least one eye. Space cannas 12 to 24 inches apart.
Fertilize cannas every four to six weeks with a 10-10-10 fertilizer. Use 3 to 4 lbs. for every 100 square feet. Water with about 1 inch of water after fertilizing, even when cannas are planted near the water.
Water cannas so the soil remains moist at all times. You may only need to water during droughts if your cannas are planted near water sources.
Dig up cannas in USDA Zones 6 and colder in the fall, after the last frost. Store the rhizomes in a box in a cool area of the home, such as a garage or basement, until spring.