How to Grow Cannas
Cannas, with their big, brightly-hued flowers and banana tree leaves look like they spring straight from the tropics, but there are actually several species native to the United States. Rainbow colored leaves and/or nonstop blooms of cannas add ambience to poolside plantings and brilliant splashes to home gardens.
Sometimes called bulbs, cannas actually grow to heights of up to eight feet in one season from rhizomes, or underground stems. You can’t beat ‘em for easy-care color and bulk in the garden. In zones 7-10 cannas will survive winter and increase in size from year to year. In cooler areas cannas are easy to lift and store during cooler months. They will also grow equally well in large containers that can be dragged inside during the dormant period.
When & Where to Plant Cannas
Plant cannas outside when the soil temperature has reached at least 50 degrees. Cannas are moisture-loving bulbs that thrive in wet soil and full sun. These plants grow to be large, so make sure they have space to spread out. If you want some extra privacy for the backyard during the summer, plant cannas as a temporary (non-evergreen) screen. Be careful about planting large stands of cannas in windy areas. The leaves can be shredded by wind, giving the plants a ratty appearance.
Even though cannas are not restricted to the tropics, they are heat lovers, so wait until people are planting tomatoes in your area to plant your cannas outside. In cooler regions you can give plants a head start by growing in containers.
Light: Cannas need full sun to reach their flowering potential. Shade encourages leggy growth that can cause foliage to flop over. Plants in shade won’t produce as many flowers, either. Several varieties are grown for their colorful leaves, which are not as bright in the shade.
Soil: Plants grow best in consistently moist soil with a pH of around 6.0-6.5. If your garden soil is acidic (low pH), add lime before planting.
Spacing: Leave 18-24 inches between plants in the landscape. If growing cannas in containers, select a container that is at least 18 inches in diameter, and plant one rhizome per pot.
Planting: Plant canna rhizomes one to two inches below the soil.
How to Grow Cannas Throughout the Season
Growth Habit: Cannas have a strong upright growth habit. Most varieties grow between 3-5 feet tall, though dwarf types will top out under 2 feet and some can grow to be 8 feet tall.
Staking: Though the plants grow to be fairly tall, they have strong, bulky stems, and rarely need to be staked.
Watering: Cannas are plants that truly need wet feet to thrive. If they’re not planted in an area that stays fairly moist you’ll need to water plants deeply once a week. Dry soil can cause the leaves to lose their brilliant colors.
Fertilizing: Cannas are big eaters. Spread a handful of slow-release or organic fertilizer around each plant at the time of planting and water well. Fertilize again mid-season. You can also mulch plants with compost or rotted manure to keep soil fertility high.
Trimming & Pruning: Deadhead regularly to prevent plants from setting seed, which will prolong bloom.
Mulching: During the summer mulch around plants to keep the soil evenly moist. In zones 7-10, add another layer of mulch in the fall to protect rhizomes from the cold as the plants overwinter in place.
Cannas: End of Season Care
After a hard frost, cut plants back to the ground. In zones 7-10 leave plants in place to overwinter. Spread a 3 inch layer of mulch or composted leaves on top of rhizomes. In zones 6 or higher, dig up rhizomes and shake the soil from them. Let them dry out for a few days and then store between sheets of newspaper in a cool, dry place.
If growing cannas in pots, cut off foliage after frost has knocked it back and bring the pots indoors to a cool, dry location. Do not water during the winter.
Canna Care and Maintenance Concerns
Cannas are almost comically easy to grow. They do not tolerate salt spray or saltwater encroachment, so they’re not the best plants for beach houses.
Dividing and Transplanting: If you want to divide cannas, cut apart the rhizomes prior to planting out for the summer. (Do not cut in the fall.) To lessen the chance of fungal infection, allow the divided rhizomes to dry and heal for a few days before planting. Make sure that each division has at least one node (bud), from which the next season’s foliage will sprout.
Pests and Diseases: There are a few pests and diseases that affect cannas, but most do not require treatment. Canna rust is a fungal problem. Control the spread and the aesthetic issues by removing affected leaves. Canna leaf rollers are caterpillars that eat the leaves. Halt their damage by regularly spraying plants with Bacillus thuringiensis (an organic soil bacterium that works as a pesticide) during the growing season.
Cannas: Extra Info
The keys to growing beautiful canna plants are plenty of water and fertilizer—compost and organic fertilizers are preferable. If plants are looking ratty and dull, simply cut them back mid-season to 6 inches or so above ground and allow them to grow out again—taking care to provide plenty of water and fertilizer as they grow back.