Updated October 31, 2024

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 I use 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 dark brown-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, but it is much smarter to act when temperatures are still in the 30s and have dipped just below 32 degrees 2-3 times.

do you have to wait for a frost before digging dahlia tubers?

No, you absolutely don’t! Many flower farmers and other dahlia growers dig their tubers up before the above-ground plant growth perishes in a frost. I personally choose to wait because I am usually cutting my flowers as long as possible, and there are plenty of other farm tasks to get to before digging tubers. The notion that a frost signals the plant to go into hibernation is something I learned years ago, but I have not personally tested whether dahlia tubers dug before or after a frost last better in overwinter storage. It may be hard to test that anyway, unless you have a perfectly controlled storage space, because every storage year is different based on temperatures, humidity levels, etc. So if you want to dig your tubers before the first frost, go ahead, and let me know how it goes!

how to dig up dahlia tubers

Before digging, I go in and cut all of my plants down using a combination of Cordless Hedgetrimmer, Loppers and Pruners. Some dahlias grow with thin stalks (easy to take a bunch of tall plants down quickly with the Hedgetrimmer), while some dahlias have huge, thick stalks that need individual cutting with the Loppers.

Cutting your plants down makes digging much easier because you’ll be able to see exactly where your digging tool needs to go. Make sure to leave 3-4 inches of dahlia stem so you can grab onto it and easily pull the tuber up after digging.

This is incredibly important: When cutting dahlia plants down with loppers, make sure to sanitize the loppers between every single plant (this is also important to do when splitting dahlia tubers — read here). This is tedious, but important work because if some plants have leafy gall or crown gall, these diseases will be transmitted between cuts. To prevent moving disease through the dahlia patch, we simply carry a bucket of bleach with us down the rows, and swirl the loppers in the bleach before cutting the next plant.

On our farm, after cutting all of the plants down, we pull up the landscape fabric. Refer to the following linked post to learn about growing dahlias in landscape fabric and why we love this method.

To dig dahlia tubers, my favorite tool to use is a short compost fork with straight tines. The most important part of digging tubers is to make sure you dig far enough away from the tuber so you don’t stick the tines into the tuber and damage it. I sink my fork into the ground about 6 inches away from the tuber, push the fork vertically into the ground as far as I can, then SLOWLY push down on the handle, using the fork as a lever to lift the tuber out of the ground.

Once the dahlia tuber has been lifted, GENTLY pull it up using the stem. I cannot stress the gentleness needed for this step. If you pull too hard, or whack your dahlia tuber around trying to get soil off it, you could break the neck and lose a bunch of tubers.

DO YOU NEED TO WASH DAHLIA TUBERS?

Honestly, I do not wash my dahlia tubers after digging. Many farmers spend long, cold hours hosing the soil off their tubers and I’ve found, after years of growing and selling dahlia tubers, that this step is not necessary for my operation. Everyone’s soil (and work preferences) are different, though. I suppose if I had super heavy clay soil caked on all of my tubers, I’d wash them off.

The few benefits I see for washing dahlia tubers are that 1) they’re clean!; and 2) washing soil off makes it easier to see eyes when dividing tubers later on.

A potential risk with washing dahlia tubers is packing them away before they’re completely dry. Washing dahlia tubers introduces lots of extra water and moisture, which we don’t want when packing them up.

LABELING DAHLIA TUBERS IN THE FIELD

If you care to keep track of your which dahlias are which, you’ll need to meticulously label them in the field. We start out by sticking a wooden plant label at the front of every variety — and I also keep a detailed map of the exact number of each variety that is planted per row, in case the label goes missing. Later on in the season once the dahlias are all bloomed, I go back and wrap the first plant of each variety with this colorful flagging tape. I’ll write the variety name on the tape using a UV-proof garden marker (FYI, Sharpie will not hold up in the sun!) and cut a 12-inch piece to double knot around the Dahlia stem toward the base of the plant. That way, when we pull up the landscape fabric and start digging, it won’t matter if the wooden sticks get lost.

I used to label my dahlia plants with these colorful plastic tree tags but I no longer use them. It turns out that they are not easier to put around the stems than the flagging tape, and they became brittle and would break from sun exposure.