How to Divide and Overwinter Dahlias in Cold Climates


How to Divide and Overwinter Dahlias

Today we're talking about overwintering Dahlias in cold climates. We begin the process by digging our Dahlia tubers from the garden bed. Tubers are ready to dig after they've been hit by a frost and start to go dormant. Leave your tubers in the ground anywhere from three days or up to a few weeks after they've been hit by the first frost, if there are no consistent freezing temperatures in the forecast. The longer you leave the tubers in the ground the more the eyes will swell so it will be easier to know where to cut if you're going to divide your Dahlias.

To make digging easier, cut off the wilted foliage. You can do this with bypass pruners, or, if the stem is very large, with loppers.

Once all the foliage is cut, it's time to dig the tubers. I like to use a garden fork for this. Loosen the soil about a foot out from the crown and try to go down deep, since you don't know how much the tuber has grown. The tuber should lift out fairly easily. Be gentle, because it will be brittle, especially in the neck area. Also, if you accidentally spear a piece of tuber or a piece of tuber falls off, don't be worried—it's all part of the digging process.

At this point, make sure you keep your label with the tuber because as you continue, and you have more than one variety, they could be mixed up.

Rinse your tuber. I find it's easiest to rinse with a garden hose. Be gentle around the area where the stem meets the roots because that's where the eyes are for next year. Cut off the stem, down to the point where it's no longer hollow along with any rotted pieces. You can also trim off any long, sort of dangly roots.

At this point, you can divide your Dahlias to have more plants for your own garden, or to share with friends. Dahlias should be divided every couple of years to keep flower production at its best. You can also wait and divide in the spring, but keep in mind that the roots will be much harder to cut in the spring. So it's sort of a trade-off, in fall it's harder to see the eyes, but the Dahlias are easier to cut. In the spring, they're harder to cut, but it's easier to see the eyes. Why am I talking about eyes? The eyes are the growing points for next year. In the fall, colder temperatures prompt a Dahlia to set its eyes for the following spring. The eyes will form at the base of a stem and look like the eyes on a potato—little raised bumps. When dividing your Dahlia, each division must have one eye and one or more larger pieces of tuber. There definitely will be more tubers than there are eyes. It's not a one to one ratio. Find where the eyes are and cut the Dahlia apart to separate them with a very sharp knife. In the image, knowing where to cut is easy because there are two stems and each have eyes and tubers attached. If there's only one stem, slice the stem in half between the eyes. Now you have two Dahlias. Sometimes you may get three or more, based on how many eyes you have. If a piece of tuber falls off but there's no stem with an eye attached to it, it's not going to grow a new plant. Toss pieces like the one at the bottom of the frame into the compost pile.

Set your tubers aside to dry for at least two to three days before storing. I find laying them in a cardboard box works the best, because you want them to dry, but not to shrivel. Set the box in a cool, dark place and once the tubers have had their drying time, we can pack them for storage.

There are several ways you can store your Dahlias, but there are two points to keep in mind. Number one, they like to be in a cool area that doesn't freeze, perfectly between forty and fifty degrees. The other point to remember is that they like to be dry, but not to the point where they're shrivelling.

The American Dahlia Society suggests suggests using plastic wrap. What you can do is take your Dahlia, let it dry overnight and then wrap it in plastic wrap with your label inside. Then you're going to put it in a cardboard box, you're going to lay it in a box, maybe five in there, and be sure you're putting newspaper or more corrugated on top because they have to be dark. Another method that you can try is using moist medium. So here we have bark chips, peat moss and sand. You would use them and have them be moist, but not wet. Take your cardboard box and your moistened medium, you're going to create a layer, put your Dahlias on top and if you're storing lots of Dahlias, you can layer them. It's important, as you're layering your Dahlias, to mist them with water, and cover them so that they're dark.

This is how we store our Dahlias at White Flower Farm.  After digging the Dahlia, and allowing it to dry, we actually recycle our bulb bags. So we're actually going to take our Dahlia and use this nice mesh bag to store in. Before we take our dried Dahlia and put it in the mesh bag, we're going to spritz it with water. So you're going to give it just a little moisture, put it in the bulb bag and put the label, with the plant name, in the mesh bag. If you don't have the label, you can make one, use a Sharpie, make your own little label, maybe using masking tape. So you've spritzed it, using the bulb bag and you're going to put it in a cardboard box, and then we take grocery bags and put them on top to keep them dark. The nice thing about the grocery bags is that allows us to check the Dahlia tubers during the winter months. At least once a month we check the Dahlia tubers, we take the grocery bag off, and we use our mister and then mist the Dahlia if we see the tuber starting to shrivel.

In late spring, your Dahlias should look similar, they will be a little harder, but the eyes will be bulging and maybe even sprouting. It's time to plant when the ground gets warm in your area.

For more information on growing Dahlias, visit our Dahlia Care page.