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Canna RHS Advice Guide 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.

By The RHS Advice Team

• Quick facts
• Cultivation notes
• Aftercare
• Water canna
• Propagation
• Cultivar selection
• Problems
• See also

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Quick facts

Common name - Canna

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Latin name - Canna

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Group - Tender perennial

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Flowering time - June to October outside

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Planting time - March and April

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Height and spread - 1.8m (6ft) by 1m (3½ ft)

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Aspect - Sunny

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Hardiness - Tender

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Difficulty - Moderate

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Cultivation notes

Cannas can be grown in borders or containers. They are grown from rhizomes Rhizomes are creeping swollen root-like structures that are actually adapted stems. Roots, stems with leaves and flowers are produced along its length. See plants such as Anemone nemorosa, bamboo, canna, border iris. (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 Mulch is a layer of material, at least 5cm (2in) thick, applied to the soil surface in late autumn to late winter (Nov-Feb). It is used to provide frost protection, improve plant growth by adding nutrients or increasing organic matter content, reducing water loss from the soil, for decorative purposes and suppressing weeds. Examples include well-rotted garden compost and manure, chipped bark, gravel, grit and slate chippings. .

Starting off rhizomes

Start rhizomes off into growth in March or early April by planting in 20cm (8in) pots using peat-free multipurpose compost Can refer to either home-made garden compost or seed/potting compost: • Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own. . 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 (50-60°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 Gradually acclimatising tender or indoor-raised plants to outdoor conditions, to toughen them up and prevent a check in growth. Place plants outside in a sheltered spot during the day then bring indoors at night for a couple of weeks. Or place in a coldframe, opening the lid during the day. 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. After planting apply a thick layer of mulch such as well-rotted manure or garden compost.

If growing in containers, use one at least 30cm (1ft) wide. Fill with a peat-free 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).

Aftercare

To help keep your cannas healthy;

• Water as needed in dry spells
• In midsummer, apply a potassium rich liquid fertiliser to plants in containers, following the manufacturers instructions
• Deadhead Deadheading is the process of removing spent flowers from plants to encourage more blooms and prevent seed production. This helps to redirect the plant's energy into producing more flowers rather than producing seeds. to encourage continued flowering
• Little pruning or training is needed. Just stake clumps in exposed positions
• When a flower spike has no more buds A bud is a small, undeveloped shoot that contains the potential for new growth. Buds are typically found on stems, where they can be apical (found at the tip) or axillary (found between leaf axils) and may develop into leaves, shoots or flowers. , 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

Overwintering

In mild areas: Plants can be left outside all year in a sunny, sheltered position. However, apply a 15cm (6in) deep layer of mulch Mulch is a layer of material, at least 5cm (2in) thick, applied to the soil surface in late autumn to late winter (Nov-Feb). It is used to provide frost protection, improve plant growth by adding nutrients or increasing organic matter content, reducing water loss from the soil, for decorative purposes and suppressing weeds. Examples include well-rotted garden compost and manure, chipped bark, gravel, grit and slate chippings. 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 Rhizomes are creeping swollen root-like structures that are actually adapted stems. Roots, stems with leaves and flowers are produced along its length. See plants such as Anemone nemorosa, bamboo, canna, border iris. 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 multi-purpose compost Can refer to either home-made garden compost or seed/potting compost: • Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own. . Place in a frost-free position for the winter. Little, if any, watering should be necessary.

Water canna

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 moist 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.

Propagation

Cannas can be propagated in spring by division of the rhizomes Rhizomes are creeping swollen root-like structures that are actually adapted stems. Roots, stems with leaves and flowers are produced along its length. See plants such as Anemone nemorosa, bamboo, canna, border iris. 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 Germination is the process by which a seed develops into a new plant. It starts with the seed coat absorbing water, expanding and splitting, which allows oxygen and water into the seed so its food reserves can be broken down and used by the embryo for growth. The first root (called the radicle) pushes into the soil to anchor the new plant in place and start absorbing water and nutrients. The first shoot (called the plumule) then grows upwards, out of the soil, towards the light. , soak seed in warm water for 48 hours or make a small nick in the seed-coat prior to sowing in peat-free multipurpose compost Can refer to either home-made garden compost or seed/potting compost: • Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own. 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)

Cultivar selection

Garden hybrids

Canna 'Striata' AGM: Golden-striped green leaves and orange flowers. Height 1.9m (6ft)C. ‘Phasion’: Striped leaves, orange flowers. Height 1.6m (5½ft)C. ‘Picasso’ AGM: Green or blue-ish leaves, yellow flowers spotted with red. Height 1.5m (5ft)C. ‘Wyoming’: Bronze leaves, orange flowers. Height: 2.3m (8ft)

Water cannas

C. ‘Endeavour’: Raspberry red. Height 1.8m (6ft)C. ‘Erebus’: Salmon pink. Height 1-1.2m (3-4ft)C. ‘Ra’ AGM: Lemon yellow. Height 1.8m (6ft)

Links

RHS Find a PlantAGM Plants

Problems

A common problem is non-flowering. This is usually due to starting the rhizomes Rhizomes are creeping swollen root-like structures that are actually adapted stems. Roots, stems with leaves and flowers are produced along its length. See plants such as Anemone nemorosa, bamboo, canna, border iris. 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 and slugs and snails.

See also

National Collection holder: Hart Canna

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