Dahlias are hardy to zone 8, which makes them tender in our 7a-5b gardens. (Depending on where you live in Western North Carolina, your garden falls into one of these zones.) Most dahlia growers dig up the tubers in fall, after a few touches of frost (when the stems are black), and either divide them then or wait for spring, replanting after the chance of frost is gone.
Will your dahlia tubers survive if you don’t dig them up?
Well, maybe. If you’ve lived in WNC long enough, you know the winters can be mild, or the winters can be a bear. If you decide to skip digging up your tubers to store them, you chance losing them. That’s a risk many people take, treating their dahlias as annuals, and simply buying more in the spring.
Still, like many perennials, division is necessary about every three years or the dahlias will stop flowering.
Follow these steps for storing your dahlia tubers:
1. Dig up the dahlia clumps.
Dig up your dahlias a few weeks after frost to allow them to go dormant; this will help the tubers produce growth eyes and thicken their skin. Dig at a wide angle, trying not to cut through the tubers. (It’s a bit like digging up potatoes in this respect.) If you do cut through some of them though, don’t worry. Tubers heal and chances are good that you have more than enough if some don’t produce. Wash the clump off and remove the root hairs. Allow the dahlias to dry outside for a few days.
2. Next, cut the stems off.
Cut the stems down to just one or two inches above the crown—this helps minimize rot. Decaying plant material from the stalk can ooze down and you don’t want that. You’re leaving the inch or two because the eyes are located on the neck of the tuber just below the stem. It helps to identify the eyes and not cut them off if some stem is left. One reason to wait until spring before dividing the tubers is because the eyes will be very noticeable by then.
Sidebar: What are eyes?
Dahlias have eyes just like potatoes have eyes. And each tuber must have a growth eye or it will not flower. In the fall, these aren’t as easy to discern, and leaving them in the ground a few weeks after frost is helpful as it causes the tubers to go dormant when they produce eyes and get thicker skins. Flag the stems of the dahlias before they die back, so you’ll find them easily when digging time comes. If frosts haven’t yet occurred, don’t wait much past mid-November to dig. You can store the clump through the winter and divide it in April, if you choose. Just skip the division and store as noted below.
3. Divide the tubers.
When you divide, you want to first remove the mother plant. It will no longer produce flowers. Use a knife like the Hori-Hori knife (a Japanese garden knife) or another sharp garden tool to gently separate the new tubers from the original plant. This is easier to do after the clumps have dried outdoors for a few days.
You also want to cut off tubers that are growing out of another tuber, as these won’t produce flowers either, and throw them away. Begin identifying the eyes at the neck of each tuber, and cut just above that. In the fall, it’s not as easy to spot the eyes on the dahlias, but don’t toss any of them out. Go ahead and store them. You’ll be surprised how many still sprout.
4. Store them carefully.
There are several ways to store your tubers, but you have to be sure they have enough air flow. Using cardboard boxes or paper bags, add shredded paper to reduce evaporation and keep your tubers from drying out. You can also use peat moss, coarse sand, sawdust, wood shavings or vermiculite. You’re trying to strike a balance between keeping the tubers dry without completely drying them out.
Store them in a cool, dry place where the temperatures will stay above freezing, but below 50 degrees. A garden shed, cellar, or garage are all good options. Plant your tubers in spring once soil temperatures are above 60 degrees or the chance of frost is past. Remember, dahlias like full sun and dry feet. Put them in a happy place and then watch them bloom and bloom!
