How To Grow And Care For Cannas

Nothing beats cannas for big, bold summer color. With flashy blooms and dramatic foliage that can reach 6 or taller, this striking subtropical perennial is an eye-catching addition to your garden or patio containers. Plant the rhizomes after the last frost. Once the weather warms up and sprouts emerge, they grow quickly and start blooming in about three months. “Cannas bloom all season long and thrive even during the hottest parts of the summer,” says grower Nikki Snow of Horn Canna Farm in Carnegie, Oklahoma. “They also do well in containers, so you can use them in pots as a living privacy screen along your patio.”

These plants often are called by the common name canna lily, but cannas actually are not lilies at all.  The name comes from the Greek word “kanna,” meaning a reed or reed-like plant. The banana leaf-type leaves and beautiful blooms grow from a rhizome, a type of fattened extension of the stalk, which resembles a piece of fresh ginger root, says Snow. Here’s everything you need to know about growing and caring for cannas in the South.

Plant Attributes

Canna Care

Cannas are easy to grow and don’t need a lot of hands-on care after planting. Deadheading faded blooms is not necessary, but it can neaten up the look of the plant. But be careful not to snip off the entire bloom because new flowers are developing underneath the spent blossom, says Snow. Hummingbirds will visit to feed on the nectar.

You can buy cannas in containers or as bare rhizomes. For rhizomes, do not plant until soil temperatures have reached 60ºF or warmer. If you plant too soon when the ground is cold, the rhizomes will sit there and do nothing, and if it’s too wet, they can rot, says Snow. When planting, set the rhizome on its side horizontally and cover with 1 to 2 inches of soil. Do not plant too deep because they love the heat from the surface of the soil, says Snow. Space canna rhizomes about 12 to 18 inches apart in the garden. In USDA Plant Hardiness Zone 8 and further south, cannas can be left in the ground over the winter. They can tolerate heat, some drought, and moist soils. In good conditions, they will spread each year in the garden.

Light

Make sure cannas receive at least six hours of direct sunlight per day in order to bloom well. They will tolerate partial sun but produce fewer flowers. If you plant in part sun, make sure your cannas receive four hours or more of sunlight. Afternoon shade can help prevent foliage from burning in hot, dry climates like the desert Southwest.

Soil

Cannas tolerate neutral to slightly acidic pH levels. They appreciate rich, moist, well-draining soils. They can do well in boggy conditions such as in a rain garden or at the edge of a pond. Clay and sandy soils can be amended with compost to improve the soil.

Water

Water cannas at planting time, then throughout the summer if it’s dry. If you are planting rhizomes, water once and then wait for the sprouts to emerge two to three weeks later before watering again. Cannas do best with a deep soaking once a week, says Snow. Aim for 1 or 2 inches of water each time. During very hot, dry weather you can increase watering to two or three times a week.

Cannas are moderately drought-tolerant once established and won't suffer if you miss a watering in many gardens. They've even been planted along highways in some states. However, cannas require more water in an arid climate or in a hot climate like southern Florida. Cannas planted in containers also dry out faster than those in beds, so you'll need to water more frequently. Add a layer of mulch around your cannas to help conserve moisture.

Temperature and Humidity

Native to South and Central America, cannas enjoy the heat and humidity of the South. They are hardy in Zones 8 to 10 and usually survive in the ground in Zone 7 with extra protection. The plants wake from dormancy once the soil warms and grow vigorously during hot weather. Rhizomes should be planted after the last frost or once the soil temperature reaches 60° F.

Fertilizer

If you like, you can feed cannas with a 5-10-5 or 10-10-10 granular fertilizer to encourage more blooms. High-nitrogen fertilizers increase the height of the plants but may result in scraggly blooms. Apply two to three times over the course of the growing season. Fertilized cannas sometimes attract more pests.

Types of Cannas

• ‘Musifolia’: This giant canna reaches heights of 8 feet or more. With bronze-striped leaves and bright red or orange flowers, it will garner compliments all season long.
• Tropicanna (Canna 'Phasion'): This 6-foot canna has foliage that can't escape notice. The deep green leaves are pin-striped with fiery orange and crimson. Deep orange flowers sit atop red stems.
• 'Australia': Dark chocolate foliage with lipstick red flowers make this variety an outstanding choice for contrast with the other greenery in your garden. This variety grows 4 to 5 feet tall.
• 'City of Portland': This long-standing favorite has dark green foliage and flowers ranging from salmon to deep coral. It grows 4 to 5 feet tall.
• 'Alaska': This pretty charmer reaches 3 or 4 feet tall and has dark green foliage with a hint of blue-green. The beautiful ivory blooms continue all summer long.
• 'Cleopatra': This incredible variety, which reaches 4 to 5 feet tall, is a chimera, meaning there’s no way to predict how the red and green variegated foliage will appear from year to year. The flowers may be solid yellow, solid red, or a combination. Every year will be different, and no two plants are alike.
• 'Durban': This variety grows 3 to 4 feet tall and has wildly psychedelic foliage with hints of yellow, green, red, and pink. The orange blooms contrast beautifully against the colorful foliage.

Pruning

Canna flowers last a few days but eventually turn brown and shriveled. If you find them unsightly, clip off the stems just below the blooms. More flowers are developing further down, and you don't want to remove them. Once all flowers on a stem have bloomed, you can cut it down to the base.

The entire plant begins to look scraggly once the first frost hits. Cut off the foliage at the base of each plant just above the soil line after the first frost, and your cannas will go dormant for the winter. Plants can suffer some damage from cold weather even in frost-free areas. Remove browning foliage at the base to tidy up the garden and reduce the number of pests overwintering in your cannas.

Propagating Cannas

Cannas have large rhizomes that enthusiastically grow and spread in warm climates. The tall plants can shade and overpower more delicate plants in the garden. Removal provides plenty of opportunities for dividing and sharing plants. You can also divide overcrowded clumps every two to three years if flowering becomes lackluster.

Division is best done in spring when the soil is warm enough to replant the rhizomes. To propagate by division, dig up a clump of your cannas and separate as desired with a spade. You can replant the clumps at the same depth in a better spot, spacing them 2 to 3 feet apart. Or, cut the rhizomes into sections for replanting. Use a sharp, sterile garden knife and make certain each section includes three to five eyes. Replant the rhizome sections 2 to 3 inches deep and space them 12 to 18 inches apart.

How To Grow Cannas From Seed

Many canna hybrids are sterile, but those that aren't produce large, dark, round seed capsules in fall that can be collected for planting in late winter or early spring. The thick seed coating should be scarified before planting. Follow these steps to grow cannas from seed indoors or in a greenhouse:

1. Scarify the seeds by one of two methods. You can nick the seed coating by lightly sanding a spot with sandpaper until you see the light-colored tissue beneath. Or, place the seeds in a bowl and pour very hot water (nearly boiling) over them. Leave them in the water for 24 hours before planting.
2. Fill 12-inch containers with fresh potting mix and lightly moisten. Plant one seed in each container at a depth of 1/4 inch. Keep the soil moist and at a temperature of 70°-75° F.
3. Sprouts should emerge in one to two weeks. Place them in a sunny window or under plant lights for 16 hours a day.
4. Fertilize plants when they are three to four weeks old. Use a houseplant fertilizer at half-strength.
5. Once each plant has two or three leaves and all danger of frost has passed, harden off the plants over the course of a week. Start in a sheltered space outdoors and gradually expose them to more sunlight, bringing them in at night if temperatures are cold. Then transplant them in the garden.

Potting And Repotting Cannas

Cannas also can be planted in containers. Opt for at least a 20-inch-diameter pot which will give you enough room for one canna and a spiller-type plant to drape over the edges of the container, says Snow. Or, plant one rhizome in a 15-inch pot. Use a high-quality potting mix and plant your rhizome horizontally at 1 to 2 inches deep, then water well.

Potted cannas need frequent, often daily, watering in summer. Place a saucer under the plant to help retain moisture. Use a slow-release granular fertilizer that is formulated for flowers according to package directions. The large rhizomes can outgrow pots quickly. If your cannas become root-bound, lift and divide the rhizomes and replant.

Overwintering

If you live in Zones 6 or colder, you will need to lift, or dig up, your cannas after the first frost and before the ground becomes frozen. Use a shovel or garden fork to lift the rhizomes, cut stems almost to the base, rinse off the dirt, then let dry. Store the rhizomes nestled in a bed of peat moss inside a plastic garbage bag; poke a few holes in the bag to permit airflow. This allows some natural moisture to be retained so that the rhizome will not dry out over the winter. Keep them in a cool spot, around 50ºF, in a cellar, basement, or crawlspace, says Snow.

In Zone 7, cut the foliage back almost to the ground after the first frost. Cover the crown with a thick layer of insulation such as straw or leaves. Gardeners in Zone 8 and warmer don't need to take extra steps to protect cannas in winter.

If you have cannas in containers and live in Zone 7 or colder, you can bring the entire pot into your garage or shed. The ideal storage temperature is around 50°, but most importantly, it must remain above freezing. Cut the stems down to the base when the plant begins to go dormant and then move your pot to a sheltered area. Do not water.

Common Pests & Plant Diseases

Deer and rodents aren’t attracted to cannas as they are to some other garden plants, such as day lilies or roses. But they may take a nibble if you have a large population of deer in your area.

The canna leaf roller causes the ugliest damage to foliage. Moths lay eggs in the developing stems, then damage is revealed as the tattered leaves unroll. If you see leaves held together with webs, unroll them to remove caterpillars or spray Bt down into the leaf. Removing foliage each winter helps reduce the population.

Slugs and snails may chew holes in the leaves but aren't usually a serious problem. Japanese beetles enjoy feasting on the flowers. You can pick them off and dunk them in a can of soapy water.

Canna viruses can be a problem, causing spotted or streaked leaves, stunted growth, and distorted blooms. Severely affected cannas should be discarded. Finally, rust is a fungal problem first detected when orange or yellow pustules appear on the plant. High humidity and inadequate sunlight contribute to the problem. Leaves may eventually yellow and large rust-colored patches can form. Remove affected leaves and dispose of them, then spray the plant with a fungicide labeled for rust. The problem can be difficult to control once it appears.

How To Get Cannas To Bloom

Individual flowers only last a couple of days, but cannas successively bloom in summer and often into October when they are hardy. The blooms look similar to an iris or lily and can be red, orange, white, yellow, or pink. Cannas take about three months to develop flowers after planting. Especially if you are growing canna as an annual, it's important not to plant the rhizomes too deep. Where summers are short, plant them about 1 inch deep so they sprout quickly and have time to develop flowers. Consider starting your plants indoors a few weeks before you plant them to extend the growing season.

Cannas bloom best in full sun. Drought or overcrowding can reduce blooming. Provide consistent moisture and divide if needed. Over-fertilizing can also prevent blooming. Use a slow-release, organic fertilizer formulated for flowers.

Common Problems With Cannas

Cannas are fairly tough plants, though you should keep an eye out for pests and signs of disease. Weather conditions can also affect plants and cause the problems below.

Tattered Leaves

While the canna leaf roller is often at the root of this problem, strong winds can also shred the leaves. Consider moving your plants if they are in an exposed, windy area of the garden. Tattered leaves can also be a sign of under watering, as discussed below.

Brown Leaves

Plants that develop brown, crispy margins on the leaves usually need more moisture. The leaves may begin to separate and become tattered. Check the soil and water more frequently as needed. Leaves also begin to turn brown as cool weather or frost arrives, signaling the plant should be lifted or cut back for the winter.