Cannas are vibrant tender perennials that produce bold leaves and showy flowers in shades of red, orange, yellows and pinks. It is a useful summer bedding plant for both containers and borders, but does well in cool conservatories in summer.
Cannas can be grown in borders or containers. They are grown from rhizomes (underground stems), which you will find for sale in late winter in bags of shredded paper, or sold loose. Cannas are easy to grow from rhizomes, but you can also buy plants over the summer.
They are tender plants, but in warmer parts of the UK you can leave the rhizomes in the ground with a covering of mulch.
Starting off rhizomes
Start rhizomes off into growth in March by planting in 20cm (8in) pots using multi-purpose compost. The rhizomes should be just covered with compost, leaving any young shoots exposed. Water lightly. Keep the rhizomes at a temperature of 10-16°C (50-61°F), such as in a heated greenhouse or sunny conservatory. If heating is not available, delay potting until April. Increase watering as growth develops.
Planting in borders and containers
Move the plants to a cool greenhouse in mid-April and gradually harden off before planting out at the end of May (or when the last frosts have past).
Plant about 75cm (30in) apart, 10cm (4in) deep. In borders, choose a sheltered, sunny spot and soil that has been improved by digging in well-rotted manure or garden compost. Also apply a general purpose fertilizer, such as growmore, at 70g per sq m (2oz per sq yd).
If growing in containers, use one at least 30cm (1ft) wide. Fill with a John Innes No. 3 loam-based compost and add a controlled-release fertiliser. Plant the rhizomes at the same depth as in borders (see above).
To help keep your cannas healthy;
- Water freely in dry spells
- Apply a liquid fertiliser in midsummer
- Deadhead to encourage continued flowering
- Little pruning or training is needed. Just stake clumps in exposed positions
- When a flower spike has no more buds, prune it down to the next side shoot where a secondary flower spike should develop
- Under glass, grow in full light but shade from hot sun. If temperatures are maintained above 10°C (50°F) cannas will remain in growth all winter and flower occasionally
In mild areas: Plants can be left outside all year in a sunny, sheltered position. However, apply a 15cm (6in) deep layer of mulch in winter and be prepared that there may be losses in very cold or wet winters.
In colder areas: Pot-grown specimens can simply be moved into a frost-free place. Otherwise, lift the rhizomes once the top growth begins to wither in autumn. Cut down the foliage and stems to about 15cm (6in). Remove surplus soil, dry and then store in trays in barely-damp wood vermiculite or multi-purpose compost. Place in a frost-free position for the winter. Little, if any, watering should be necessary.
In summer, water cannas (often bred from Canna glauca) can be placed in containers in ponds with no more than 15cm (6in) of water over the roots. They are also suitable for well-watered borders or conservatories where potted plants can be stood in deep saucers of water.
Before autumn frosts, bring plants from outdoors into a frost-free greenhouse or conservatory. Keep the pots moist but not saturated. In April, increase temperatures and plant the sprouted plants out in late May when the risk of frost has passed.
Cannas can be propagated in spring by division of the rhizomes into sections, each with two or three growing points. Cannas can also be propagated from seed, although cultivars will not come true. In a good summer, many cannas will set seed that can be sown the following spring. Seed-raised plants usually flower in their second year.
If sowing seed, follow these tips for the best results:
- To speed germination, soak seed in warm water for 48 hours or make a small nick in the seed-coat prior to sowing in multipurpose compost at 21°C (70°F). Cover the seed with their own depth of compost
- Pot on soon after germination into individual containers
- Keep at a temperature of about 16°C (60°F)
Canna 'Striata': Golden-striped green leaves and orange flowers. Height 1.9m (6ft)
C. Tropicana ‘Phasion’: Striped leaves, orange flowers. Height 1.6m (5½ft)
C. ‘Wyoming’: Bronze leaves, orange flowers. Height: 2.3m (8ft)
C. ‘Endeavour’: Raspberry red. Height 1.8m (6ft)
C. ‘Erebus’: Salmon pink. Height 1-1.2m (3-4ft)
C. ‘Ra’: Lemon yellow. Height 1.8m (6ft)
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A common problem is non-flowering. This is usually due to starting the rhizomes into growth late, but can also be caused by a lack of water or poor soil fertility.
Plants can be infected with virus, which may be indicated by distorted foliage, or a yellow streaking, or mosaic pattern on the leaves. There is no cure for viruses and infected plants should be destroyed.
Other problems include usual garden pests such as glasshouse red spider mite, aphids, slugs and snails.