Everything you need to know about growing cannas
Cannas are one of the most tropical-looking plants. They tap into today’s trend towards exotic gardens.
But they can be grown in quite temperate climates.
I asked Stephen Ryan, Australian gardening broadcaster and owner of the Dicksonia Rare Plants nursery, for his advice on choosing and growing canna lilies. Stephen also has a YouTube channel, called The Horti-culturalists, where he talks about plants.
How to choose cannas
‘Although you may be choosing them for their flowers, they’re a wonderful foliage plant,’ says Stephen. ‘So think about whether you want red, green or grey based foliage.’
He also says that cannas come in a range of heights. ‘Some dwarf plants are less than a metre high, while the very tall ones can be up to three metres.’
In his opinion, the taller cannas look better in a border. ‘To my mind, there’s not much point in the smaller ones.’
Tubers or fully grown plants?
If you buy your canna lilies as tubers or rhizomes, Stephen advises you to look for a decent-sized plump rhizome, with several ‘eyes’. ‘A small piece may struggle to re-establish.’
If you live in a cool climate, plant the rhizomes up in pots any time from early spring onwards and keep them in a sheltered spot.
However, buying cannas as fully grown plants is a good option, ‘because then you know exactly what you’re getting.’
‘Look for healthy looking leaves and a canna with several good stems growing from the base,’ he says.
Canna virus is a problem all over North America, the UK and Europe, so it’s a good idea to check the leaves. They should look healthy, not mottled or withered.
When to plant cannas
Stephen says you can plant the rhizomes in pots from early spring, but keep them somewhere sheltered and away from frosts. Plant them when the risk of frost is over.
He used to stay at Great Dixter when Christopher Lloyd was still alive:
‘Christo used to plant cannas in polystyrene boxes, then he’d keep them until the mid-summer flowers were over. He’d remove plants from the Long Border once they were past their best and pop the cannas – ready to flower – into the gaps.’
This makes them a good plant for extending the interest of your border later into the summer.
They’re also very popular with pollinators, so are good if you want to encourage wildlife in your garden.
Cannas in pots
Canna lilies do well in pots. Choose larger pots for the larger cannas and remember that they are tall plants so they may be knocked over in the wind. The pots below show cannas at Kew Gardens. The taller cannas in pots are surrounded by smaller pots which will stop them being blown over.
Can cannas survive winter?
‘Cannas are tropical plants,’ says Stephen. ‘So they’ll have to be dug up and over-wintered in harsh climates.’
However they can survive mild temperate winters. Stephen lives near Melbourne in Australia where winter temperatures can drop below freezing. He doesn’t dig up his cannas, and just covers them with a layer of mulch, straw or bracken.
And in the Salutation garden in Kent (UK), head gardener Steven Edney also leaves his cannas in the ground. ‘Once the foliage has collapsed after a frost, we fold it over the crown to help protect it, then we cover it with mulch,’ he says when talking about plants for late season colour.
Where to plant canna lilies?
They need an open, sunny spot in the border, according to Stephen Ryan.
Cannas are also very hungry and thirsty plants. ‘I advise people who plant cannas to plant them under a dripping tap and then tie a horse to the tap,’ says Stephen. ‘You can’t over-water or over-feed a canna.’
So add plenty of mulch when planting and top it up over the season.
How to prune cannas
Stephen recommends tidying up your canna flowers once they begin to fade. Some cannas drop their flowers before they go brown, but if not, simply pick the dying petals out.
Once the whole bloom has died, feel down the stem for the next flower coming up. It will feel like a bud on the side of the stem. Cut the canna stem down to just above this bud and the new flower will soon bloom.
Once the canna has blossomed two or three times, and you can’t feel any more buds along the stem, Stephen recommends cutting the stem to the ground. ‘That will stop it setting seed and will encourage other stems to spring up.’
The video below shows this interview with Stephen on growing cannas. If you’d rather fast-forward to the pruning and tidying advice it starts at 5 minutes 30 seconds.
Slugs and snails enjoy the big paddle-shaped leaves, so be vigilant.
And canna virus is common in the Europe, USA, the UK and parts of Australia. It makes the leaves look mottled and affects the vigor of the plant. It’s one good reason to buy cannas when they are already in leaf, so you can check that they look healthy.
Where to buy cannas
Most garden centres sell cannas now. However these cannas will probably be exported around the world in large quantities, so may be more vulnerable to virus. It may be better to find a nursery where they are grown, so you can inspect for virus.
It may seem rather cheeky to title a post ‘everything you need to know about cannas’, but the emphasis here is on the word ‘need’. These are the facts that will get you started.
After which you could – but you don’t have to – spend a lifetime getting to know these brilliantly colourful and sculptural plants.
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