Dahlias are tender tuberous perennials. A heavy frost will kill off the foliage, but wet, cold conditions in poorly draining soil will finish off the tuber, the source of next years growth. My soil is fairly sandy and free draining, and I would probably get away with leaving the tubers in the ground, but I’m not confident enough of that to risk all of my dahlias. I’m leaving some of the bedding dahlias in the ground, but most I am going to overwinter. I did this for the first time last year. I lost a couple of pieces of dangly tuber to rot but nearly all made it through intact.
Once the foliage is frost-blackened, the first step is to carefully remove the tubers. I cut away the foliage leaving a 6 inch portion of stem.
I used a broad garden fork, pushing it in about 8 inches from the stem and levering the tubers out. I figured this was far enough away to avoid damaging the tubers. A couple of the larger plants needed a second or third levering from a different direction.
As dahlia tubers all look pretty similar I labelled them as I removed them from the ground, just tying a plant label round the neck. Once labelled I took them off to the shed to dry off, leaving them in the shed for a couple of days, upside down on some newspaper.
When dry, I brushed off the soil, leaving the tubers as clean and dry as possible, trimming off any of the fine roots.
They will be dormant for the winter, the important thing is to avoid the tubers getting damp, or they will go soft and rot off. Last year I stored mine in dry compost, in a cardboard box that I kept in the shed where it is dry and frost-free. This year I am using vermiculite in a couple of plastic tubs. I put a layer of vermiculite in the bottom of the box and placed the tubers stem side up.
I then covered them with more vermiculite, leaving the tops of the stems exposed.
Sand or sawdust would work as well, I reckon. The benefit of vermiculite is that it will absorb any excess moisture. It’s also what I had handy.
That’s it. I shall leave them be in the shed until late February, early March when I plan to bring them into growth and take some cuttings. More dahlias!
For those tubers left in the ground, I have covered with a thick mulch of leaves and garden compost, a natural duvet. Fingers crossed, they’ll be OK. I’ve added a label so I don’t disturb or amputate any parts of the tuber when fiddling about in the border over the winter.
I’ll be back soon with more propagation shenanigans.
All of my tubers stored this way dried out and died! My mistake was not to moisten them when putting into the vermiculite, and I should have checked them every couple of weeks to make sure they weren’t drying out. An occasional spritz with a hand spray would have been enough. So that’s a bummer. On the plus side, all the tubers I left in the ground were fine, all came back to life this spring. This winter I am leaving all of mine in the ground, with a thick duvet of leaf mold or compost. This is safe to do as my soil is free-draining – it’s getting soggy that the tubers don’t like, rather than the cold. You win some, you lose some.