Geraniums, over winter
Thank you for contacting us,
There are many different ways to overwinter geraniums, and there doesn't seem to be agreement on one BEST way to do it. It sounds like you already have a great place to store them, so it should not be too difficult, especially with your success saving Cannas.
If the geraniums are in the ground, dig the plants before a killing frost and cut them back to no more than six inches high. You may want to try and root some of the shoot tips for more flowers next year, but if not, you can discard the tops.
The ideal storage location is about 40-45 degrees (Fahrenheit) with little lighting. Too much light will start them growing again. You can pack bare root plants together in a storage container, and lightly cover them with sawdust or a very light soil mix. By keeping the roots apart, you minimize the risk of rot spreading from one to another.
You can store potted geraniums in their containers, and just cut back the tops.
Check the roots or soil periodically through the winter, and water just enough to keep the plants from shriveling or drying out. It does not take much; you don't want them to sit in water. Over watering leads to rot.
In early April, (in the Spokane area) you can get them started for the year by potting them up in a potting mix or soil. Water well, and put them in a sunny location. They should begin growing, and be ready to plant outside when the danger of frost is past.
Thank you again for contacting us, please let us know if we can answer any other questions.