Dahlias are one of my favorite flowering plants, with a long bloom season, from early summer to the first frost. Deer and rabbits seem to have no interest in eating these showy plants. While they are usually grown as an annual flower, it is easy to store the roots over the winter and enjoy the same plants for many years.
Here are the steps for overwintering:
Wait until a few days after we have a frost that causes the foliage and flowers to die back. You must dig them out before the soil freezes.
Make sure you have separated and labeled the roots by variety.
Cut the stems back to a few inches above the soil, using a clean, sharp pruner. It is a good idea to disinfect the pruners between plants using a 10% chlorine bleach solution. This will discourage the spread of fungus.
With a spading fork, dig about 12 inches from the plant, lifting gently as you go around.
Once the ground is broken up, lift the entire plant out. Carefully remove soil around the roots. Dahlias are tubers; their root system includes swollen underground storage organs, similar to potatoes. Like potatoes, the dahlia tubers form eyes, new growth points for next year’s plants. For dahlias, those eyes will be at the top of the tubers adjacent to the stem from this year’s plant. If you break an eye off, it will not be able to sprout in spring. Once most of the soil is brushed off, use a garden hose to wash off the remaining soil.
Place the tubers on a flat clean surface; cardboard works well. Allow them to dry completely. It will take several days.
You can apply a fungicide to the tubers prior to storage. If your plants had fungal issues, like powdery mildew, this is probably a good precaution.
Place your tubers in a cardboard box and lay them flat. If you are creating several layers, put some brown paper between layers. For moisture control, you may want to put them in peat moss or wood chips. The goal is to keep the tubers moist enough to prevent drying, but dry enough to prevent rot.
Store them in a dark place where the temperature will stay between 40 and 50 degrees. An unheated garage can work well, if you remember to bring the box in during sub- zero nights. Keep a refrigerator thermometer nearby to monitor the temperature. Check moisture levels every few weeks and spritz with water if too dry. Too dry is better than too wet.
In spring, you will be able to plant the roots once the danger of frost is past.