Winterizing Your Dahilias
To dig? or not to dig?
Dahlias can be a tender annual and in my experience, in growing and caring for dahlias for years, the best way to ensure your dahlias make it through the winter is to dig them. I have tried both digging and leaving them in the ground over winter and the only pro I found to leaving them was convenience -however, this impacted the following growing season for me.
First, dahlias are hearty to zone 8. Living in the Pacific Northwest, we are just on the hub of this hardiness zone. If you do choose to leave your tubers in the ground over winter, cut them back to where the stock meets just below the ground, shelter with a plastic painters drop-cloth, then cover with 6-8 inches of dry mulch. Be aware that if you are anticipating a wet or severely cold winter, this may not be the best option as the tubers can easily be susceptible to rot. Last winter I kept mine in the ground. We had one of the worst winters hit the Pacific Northwest in decades. This is when I learned to start checking The Old Farmers Almanac on upcoming season weather projection.
My winterizing technique actually worked wonders; I didn't have a single tuber rot or freeze. However, I did notice that my tubers produced significantly more greens than buds this year. This can be a sign that the tubers didn't have enough room to breath and in return they stopped flowering. You can see this affect as my once 3-6" tuber has multiplied into a tree-trunk like form!
After digging, you have the choice to separate now or in the spring. I decided to wait until the spring as this process was overwhelming in itself. (See how many I would have to divide! Wowza).
Once you have them dug and/or dug and divided, you will want to clean them off from dirt and debris. Store your tubers in a cardboard box or breathable container packed with Peat Moss. Keep your container in a dry, cool place with temperature roughly between 40 and 50 degrees.
For tips on how and when to winterize, check out Swan Island Dahlias. Not only do they have simple tutorials, but they also provide videos for more visual learners.