Dahlias are sub-tropical flowers, indigenous to the New World. While it's their showy blossoms that we rightly concentrate on, the real story behind growing this plant successfully lies underground -- in the dahlia tubers. This tutorial will show you one possible way to store the tubers for winter.
Dahlia tubers are sometimes referred to as "bulbs," although they are not true bulbs; nor are they "corms," another term you'll sometimes encounter. Hardy only as far north as planting zone 9 (or, at best, 8), the tubers must be dug up and stored for winter in cold climates, as you would dig and store elephant ears and canna bulbs.
So when is it time to dig them and store them away for winter? Well, fortunately, you don't have to rely on notes, and you don't have to worry about missing any strict deadlines -- as long as you observe your garden regularly. For Mother Nature let's you know when you need to dig dahlia tubers in no uncertain terms! Take a look at the picture above. When your plants look like this in fall, Mother Nature is speaking loud and clear: "Get ready to dig your dahlia tubers and store them for winter."
Judging from the picture above, you might think the plant is totally dead. But it's not! Only the flowers and above-ground vegetation have really been killed. The dahlia tubers are still alive underground. What you're seeing in the picture is the result of a frost. Jack Frost is the messenger Mother Nature sends to tell you it's time to store dahlia tubers for the winter.
But don't be too hasty about digging them. Frost stimulates the dahlia bulbs to begin setting eyes (sort of like the eyes on potatoes) for next year. Upon the arrival of fall's frost, in other words, your bulbs start working on their plan for next year's growth. So hold off on digging until a week or two has passed. The exception to this rule would be if you hear a freeze is on the way in your area: a freeze would damage the bulbs, so you would have to dig them early and hope for the best next year.
I will not push the potato analogy too far, though. Potatoes develop eyes even when you don't want them to; I cannot tell you how many times I have left a bag of potatoes behind to go on vacation, only to return and find little but eyes left to them! Dahlia tubers, by contrast, are much less willing to "give you the eye."
The purpose of this tutorial is to show you how to store dahlia tubers for winter. Let me note, right at the outset, that different gardeners have been successful (or unsuccessful, as the case may be) with different methods for storing dahlia tubers. In fact, when you consider all the different variables in the project (the precise temperature at which they are stored, the type of storage medium used, etc.), it would not be too much of an exaggeration to say that there are as many possible ways of storing these beauties as there are varieties of them! Success is not guaranteed with any of these methods, so I suggest that you tweak my instructions as needed, in the spirit of experimentation.
It's important to get it right, because your dahlia tubers will spend a lot of time in winter storage if you're a Northern gardener. My plants here in zone 5 generally get frosted in early November. As "summer bulbs,"-- I won't be able to re-plant dahlia tubers for many months (see the end of this article). So my dahlia tubers sleep away a good portion of their lives!
I usually do not fuss with the storage method laid out in this tutorial, myself. I grow my dahlias in pots, then bring the pots into a cool (but not freezing), dry area for the winter (if I can find one!). Sometimes they make it, sometimes they do not. But in this tutorial, I provide the basic outline for how the "experts" say you should store dahlia tubers for the winter. Supposedly, this method increases your chances of having the dahlias survive. I have not, however, found this to be the case in my own experience: I've had at least as much success with my own preferred method (i.e., keeping the tubers planted in containers year-round). Nonetheless, as an alternative, you should be aware of the technique recommended by the experts, which is why I'm presenting this tutorial.
On Page 2 we'll begin at the beginning: with the digging....