Pictured is a canna lily in bloom.
image by Catherine Munro: Commons.wikimedia.org
Canna lilies are tropical perennial-flowering plants grown from underground rhizomes. Popular for their large red, pink and yellow summer blooms; tall stalks; and large, colorful foliage, cannas are hardy in U.S. Department of Agriculture (USDA) Zones 8 through 11 and successfully grown as annuals in cooler climates. Cannas are accepting of various planting conditions, from containers to boggy soils, and are commonly grown in beds, at the backs of borders and in en masse plantings.
Select a location with full-sun exposure to grow your canna lilies, whether in the ground or in a container. Though they prefer full sun, cannas will tolerate a few hours of partial daily shade without affecting bloom performance. Maintain a nutrient-rich soil that will hold moisture well around the canna's roots. In drier climates, mulch around the base of your plants with an organic material such as shredded bark or cocoa hulls to raise the soil's organic content, tamp down competitive weeds and prevent moisture loss to evaporation.
Water your canna lilies so that they have constantly moist soil. Unlike most bulbs or rhizomes, cannas will accept and thrive in wet soil. In the heat of summer or dry climates, water your cannas once every five days or so and roughly every eight to 10 days during the rest of the active growing season. Use your fingers to dip test the soil to gauge the moisture level and to know when to apply water. Do not let the soil around the rhizomes dry out between waterings.
Feed your canna lilies beginning in the spring with a balanced slow-release granular fertilizer to boost both foliage growth and blooms. Always apply fertilizer over wet soil, and water well. Follow the dosing regimen recommended on the product package, and always err on the side of underfertilizing to prevent the buildup of excess mineral salts in the soil.
Deadhead canna flowers when they fade to encourage fresh blooms. Canna lilies do not require regular pruning, but keep an eye on the plants and prune away any damaged or diseased flower stalks and leaves with clean, sharp secateurs as soon as you see them, and discard any diseased material in your trash bin, bypassing the compost pile.
Dig and store your canna bulbs indoors for the winter in USDA Zones 7 and below, where they cannot overwinter in the ground. Carefully dig the rhizomes from the soil after the first frost in the fall, brush off the soil, and nestle them in a shallow box of sand or peat moss. Do not cover the bulbs completely, just about 3/4 of the way. Set them in a cool but frost-free spot out of the sun, with a garage or cellar being ideal.