We live in a growing zone that is too cold to leave dahlias in the ground over winter. Every fall, we diligently dig up our tubers and place them into storage for the winter. Although time-consuming, this process is necessary to protect our inventory for the following year.
In the spring of 2022, we found a few "volunteer" dahlias emerging from our gardens. These likely had been tubers that broke from the clump when we dug up our tubers in the fall. They were tubers buried deep in the soil, and were protected from the freezing temperatures over the relatively mild winter.
In the fall of 2022 and again in 2023, we chose not to dig up all of our tubers. We left some of our dahlias in the ground as an experiment to see whether we could successfully overwinter them. The winters of 2021, 2022, and 2023 weren't particularly cold, and most of the tubers we overwintered emerged in the spring. We mulch heavily with shredded leaves, covering the dahlias with a 6 to 8-inch layer for protection.
RISK
The downside to this method is that the dahlia tubers are vulnerable to voles. The voles like the protection of the shredded mulch, and will seek out and consume the dahlia tubers.
REWARD
In the photograph above, you can see the size difference between the dahlias that had been left in the ground and those started indoors 6 weeks before our last frost date. We gained weeks more blooms with the dahlias that had been left in the ground.
So far this winter has been unusually cold, and for an extended period. We may not be so lucky overwintering, but time will tell.
More later this spring...