Dahlias bring beautiful late-summer flowers to our gardens, but they get hot by frost in the autumn. Which? Gardening magazine trialled different overwintering methods to find out which works best:
Caption: Dahlia 'Bishop of Llandaff' is just one of the beautiful varieties you can choose from
Lifting dahlia tubers and overwintering indoors
The best way to overwinter dahlias is also the most labour-intensive. We lifted our dahlias tubers, dried them and stored them in a frost-free shed. We potted them up in spring, and kept them in the greenhouse before hardening off and planting them out after they had already put on some growth.
It's this extra care that makes the difference with dahlias. When planted out, our lifted plants put on the most growth and started flowering earlier than the other methods.
Caption: Lift dahlia tubers when the frost blackens the leaves in autumn
Other methods we tried:
In the mild winter of 16/17, tubers mulched and left in the bed overwintered well in both Glasgow and Yorkshire, although the plants weren't the tallest in our test by mid-summer. This surprised the Glasgow gardeners, who usually have to dig up and store their tubers, as they rot in the wet, clay soil.
We tried two methods of increasing our stock of dahlias. We divided some tubers into two or three pieces and this worked well. The plants were small and straggly by mid-summer, but soon bulked up, making this an easy way to grow new plants. We also took basal cuttings that were slow to establish and slower to grow than dividing the tubers.
Caption: Dahlia cuttings are slower to grow than dividing dahlia tubers