Updated December 5, 2022

If you’ve struggled with deciding when to dig up your dahlia tubers at the end of the season, you’re not alone. There is a fear that if you leave them in the ground too long then they will freeze entirely and die; however, I have found that this fear is mostly unwarranted for the first few weeks of winter in my Western New York Zone 6b. It takes one hell of a deep freeze to completely kill hibernating dahlia tubers.

So how do you know when your dahlias are ready to be dug up from the ground and stored inside for the winter?

The main signal for digging dahlia tubers is when all the above-ground green growth has turned black (some parts, like the blossoms, may just turn brown and dead looking, but the stalks will turn black). Please reference the photo below. I allow my plants to endure 2-3 frosts before digging them from the ground. This signals to the tubers to go into hibernation mode as the plants’ starches divert down into the tubers in response to the frost.

Dead dahlia foliage can be seen in top row.

It is very important you do not leave your tubers in the ground when temperatures drop below 30 degrees, when the ground is likely to freeze solid. There have been times I’ve allowed this to happen without consequence. It is much smarter to act when temperatures are still in the 30s but have dipped below 32 degrees 2-3 times.

Before digging, you’ll want to go through with a strong pair of Loppers and cut off all the tops of your dahlia plants. This will make digging much easier so you don’t end up with a mess like this:

If you care to divide and sell/give away any of your tubers, you’ll need to meticulously label them. My favorite labeling method is colorful plastic tree tags. I label all of the tubers on planting day by anchoring a tree tag next to the tuber with a 6-inch landscape pin. The permanent marker you use must be for outdoor purposes — this is the best marker. FYI, Sharpie markings will wear off over the course of the summer. Around Mid-September, when the dahlias have formed their thick stalks, I attach the tree tag directly to the stalk using a zip tie. I usually leave the plant tags attached until I am ready to divide them in the late winter so there is absolutely no guess work or confusion over which tubers are which.

Here you can see tree tag labels have been added just after planting.

Here, you can see the dahlias have come along nicely a few months later (to the left), mulched with straw to keep weeds down and moisture in.

Admittedly, the tree tags and zip ties use a lot of unnecessary plastics; however, mice and small vermin will not chew through them. This has been a problem for me in the past, so I have to use a labeling method that will hold up. When possible, I always save tree tags and reuse them.

Once your dahlia tubers are dug up, you’ll need to know how to store them! Please reference this blog article for proper storage and mitigating mold issues over winter.