Cannas are bold, exotic looking plants grown for both their attractive flowers and the foliage. Flower colours include white, ivory, yellow, orange, pink, and red and their multi-colours.
The large, banana-like foliage may be green, bronze-burgundy, or variegated in a striped or marbled pattern.
In addition, many grow large, attractive fruits, which eventually give us seed for growing new plants next year. If seed is not wanted, then extra flowers can be encouraged by dead-heading after flowering.
Cannas perform best in moist, well-drained soils in full sun. At a minimum, water at least once a week during dry weather, however, a daily watering regime will be well rewarded.
To promote growth, fertilise once a month with a balanced garden fertilizer such as Growmore. Fortnightly feeds of Miracle Grow can produce amazing results.
Remove spent flowers to promote additional blooming. While cannas have a few insect and disease pests, none are considered serious.
Cannas are usually grown from rhizomes planted directly outdoors after the danger of frost is past (Late April in Normandy) or started indoors in large pots in March.
Rhizomes should be planted 10-15cm (4″-5″) deep.
The most popular seed-grown cannas are from the Tropical Series and include ‘Tropical Rose’ (All-America Selection in 1992), ‘Tropical Red’, ‘Tropical Salmon’, ‘Tropical Yellow’, and the recent ‘Tropical White’. These usually grow 60-100cm (2′-3′) tall.
Seeds should be sown indoors in mid- to late-February in a good multipurpose compost.
Canna seeds have an extremely hard protective coating that is impermeable to water. You can help the germination process by removing a bit of the seed coat through a process called scarification. Prior to planting, take a piece of sandpaper and sand the end of the seed until you get through the black seed coat. You’ll know that you’re through when you see the white endosperm. Basically, what you’re trying to do is make a hole in the seed coat so that water can get through. Now soak overnight in warm water.
Lightly cover the seeds and water them. Maintain a temperature of 21-24°C (70 to 75°F). Germination should occur in 7 to 14 days. Keep the growing medium moist, and do not over-water, as more seedlings die from that cause than from neglect.
When seedlings are large enough to handle, transplant them into individual pots.
Plant outdoors after the danger of frost is past. They should flower about 90 to 120 days after the seed was sown.
In most areas of Europe, cannas are tender perennials. Cut plants back to 15cm (6″) above ground a few days after a hard, killing frost. In southern Europe it is sufficient to mulch and leave until spring, when they can be lifted for dividing.
In northern Europe you must carefully dig up the canna clumps with a spade or fork. Leave a small amount of soil around the rhizomes. Allow them to dry for several hours. Store in large boxes, wire or plastic crates in a dry frost-free location, but at a temperature no higher than 10°C (50°F).
Large clumps can be divided in the spring before planting. Each section should have at least 3 to 5 buds to guarantee new stems.