Overwintering borderline exotic tubers such as Cannas and Dahlias

Although it’s now late October many of the more tender plants are still looking excellent here at the Exotic Garden in Norwich, with two plants in particular growing really well, enjoying the cooler days and nights – the Dahlias and Cannas.

DahliaImage above: Dahlia ‘Pooh’

Many enthusiastic gardeners dig up them up for storage at the beginning of October which is far too soon as they are still in flower.

For those of you who haven’t grown Cannas before – they are ridiculously exotic over-the-top plants grown their fantastic foliage which range in colour from green to darkest purple, often with very large gladioli-like flower on top. In the cooler days of September through October, plants such as these put on masses of growth. As the days and nights cool down they build up large tubers to take them through the cold winter months. Cannas can be left in the ground until the first frosts blacken their leaves, which is often not until well into November here, though you can dig them up earlier if you wish.

Lobelia cardinalis & Canna Pretoria in the Exotic GardenImage above: Lobelia cardinalis & Canna ‘Pretoria’ in the Exotic Garden

They should be dug up and all the top growth removed down to about 4-6ins above ground level, then placed in a plastic pot (I use the black ones) that are only slightly bigger than the tubers, then filled with a mixture of general potting compost mixed with composted bark chippings. If, like me, you have a lot of cannas, they can be stored in a similar mix, but using large slated crates instead of pots, that will hold a dozen or more tubers depending on their size.

I store my tubers frost free under a greenhouse bench, but they would be equally happy in a garage with a blanket over them to keep out frost or any cool frost free place that isn’t to damp, as they need to be kept on the dry side to prevent mould (botrytis) forming.

Dahlias can be stored in the same way though personally I leave mine in the ground as most are pretty hardy here. If you live in a frost prone area a mulch of compost or something similar can be used to a depth of about 6ins deep which will keep out the severest frost.

Dahlias and cannas can be bought during the winter months and stored ready for planting in the spring.

Overwintering Canna plantsOn the right there is a short video we made a couple of years ago about overwintering Cannas you might be interested in.

We will be writing much more about the step by step process of digging up and storing tubers in the next few weeks when we actually get out and start digging.

Further information:
Video – Overwintering Cannas
Our selection of Cannas to buy
Top Tips for keeping the tropical feel to your garden this Autumn
Protecting our tender exotics for winter & 7 things to do right now!
How to brighten up your windowsill using bulbs this winter

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