Do I need to lift dahlias for the winter?

In one of my previous posts, I mentioned certain gardening ‘myths’ that needed busting and asked you to let me know about yours.

Tony Davidson from Leeds asked: “Surely recommending that the non-cold-hardy plant dahlia is allowed to get frosted before lifting the tubers is a myth, perpetuated by dahlia nurseries so you have to buy more!” Well, actually not, Tony. Once the foliage has turned black and plants have died back, the tubers will have ‘ripened’ and prepared themselves ready for winter. Tubers dug too early are still ‘green’ and will not store properly or as well. Also, the dahlia tubers carry on growing and swelling right up to the last moment, so lifting them early reduces the health and size of next year’s plant and the number of flowers it will produce.

dahlia cafe au lait — To get a good dahlia show next year you’ll need to lift the tubers, or at least cover with a layer of mulch to protect from frost. Image: Adobe Stock

To lift or not to lift? That IS the question

Then, of course, the next question is: do I lift or do I leave? Well, if you’re a betting person and like to take a bit of a gamble – then leave them in the ground. But if the tubers become frozen they will die. If you prefer to place your money on a certainty – and you have the facilities – lift them and store them somewhere frost-free for the winter. If you leave them in the ground, the very least you can do is give them a bit of a fighting chance against very cold weather by covering the soil around them with an insulating 15-20cm (4-6in) thick protective layer of straw, compost or bark chips. Dahlia tubers in pots are even more susceptible to cold and certainly should be overwintered in a frost-free structure. But to be on the safe side, it pays dividends to lift the tubers.

How do I lift dahlias?

Start by cutting down the stems to 10-15cm (4-6in) from soil level.
Then lift the tubers with a garden fork, taking care not to damage them.
Clear away as much of the adhering soil as possible – some people actually wash their tubers!
Don’t forget to tie a label around one of the stems with the name of the variety.
Stand the tubers upside down in a dry, airy, frost-free place for a few days to allow excess moisture to drain from the stems. More soil may have dried and can then be easily removed.
Then pack the tubers in boxes or crates filled with just-moist compost, coir, sand or similar material. Make sure the packing material is kept clear of the crown (where the stems join the tuber) or rot may set in. Keep them in a frost-free but cool place over winter, and check them regularly to ensure they don’t dry out and shrivel up, and for any signs of rot or other diseases.
You can lift and store canna tubers in the same way.

Woman pruning dahlia stems to prepare for lifting and overwintering — Start by cutting down the stems to 4-6in from soil level. Image: Adobe Stock

Woman cleaning soil from dahlia tubers — Clear away as much of the adhering soil as possible. Image: Adobe Stock

Woman washing dahlia tubers before overwintering — You can wash your tubers if you prefer. Image: Adobe Stock

dahlia tubers drying in afternoon sun before overwintering — Allow the tubers to stand for a few days in a frost-free place to drain the excess moisture from the stems. Image: Adobe Stock

Video bingo

The other tubers you should be thinking about are those of the perennial, tuberous-rooted begonias – and these definitely need to be brought indoors. If you want to know what to do with them and how to do it, then watch the video I filmed on overwintering begonias.

The practical videos you’ll see here on the website were filmed with videographer, Dave Futcher, at Capel Manor Gardens in Enflield. If you fancy a visit, it’s a brilliant garden providing loads of great ideas for your own garden. While you’re there, you could try playing Richard Jackson Video Bingo – working out exactly where we’ve filmed each of these videos! Just don’t shout out “House” too loudly when you find them all!