from The Addicted Gardener column in The Westwood Press
Several people have written to ask when they should dig up their dahlias and what procedure is best for storing them over the winter. Since frost is nipping at our heels, it’s a great time to address this topic.
If you are heading south for the winter, you can dig your dahlias now; however, it is best to wait until after a hard frost when the stalks turn black. When this happens, cut the stalks back to four to six inches and dispose of them. Leave the tubers undisturbed for one to two weeks before you lift them. That helps the tuber start to form a protective skin on its outer layer and, because the tuber will begin to push new growth, the eyes that will become next year’s leaves and flowers will become more prominent. As long as the ground is not frozen, your tubers will be safe underground.
I prefer to use a garden fork to harvest the tubers. A pointed shovel is fine, but is more likely to damage the ends of some of the longer tubers. If you cut part of the tuber off with the shovel, it won’t affect growth next year as long as the cut has calloused over.
Dig and lift your tubers and set them in the shade or inside where you will process them. At this stage, you have two choices. Rinse off the dirt with a gentle spray of water or leave the dirt on the tubers. If you wash the tubers you must tend to them within a couple of days or they will shrivel. Leaving the dirt on will allow you additional time to prepare them for storage.
The dahlias should be laid out to dry so a skin (much like the skin of a potato) forms on its outer layer. This protective skin is what helps the tuber survive the winter. The feeder roots should be trimmed off along with the six-inch stem you left on the plant when you removed the foliage. Turn the tubers over so any water left in the hollow stem will drain.
You may divide the clump in the fall, cutting single tubers from the crown with a sharp knife or scissors and letting the cuts heal over before storing them. These divisions must have an eye if they are to produce flowers next year. If you can’t find the eyes, you can divide the clump into several sections before storing them. I choose to divide my tubers in the spring because it is easier to see the eyes. The downside is that the hardened tubers are more difficult to cut.
You can store your cut tubers in horticultural vermiculite or slightly dampened peat moss. I prefer to leave the dirt on the clump of tubers, brushing off as much as possible without damaging the necks (the weakest point of the clump). After the skin has formed and the feeder roots removed, I wrap each clump in two layers of newspaper, top side down, and put it in a plastic grocery bag with a label, tying the bag once so it’s easily opened for inspection. The paper absorbs any excess moisture that the tuber gives off, and the plastic holds moisture in. You can then store the individual bags in a heavy, waxed cardboard container or, if you have a problem with mice, in a covered plastic container that has been pierced to allow air circulation.
Store in a cool, dry area where the temperature will remain at 40-45 degrees Fahrenheit for the winter and where the tubers will not freeze. If the tubers freeze, they will become mush and will smell like rotted potatoes. If they are in too warm an area, they will dry out and become petrified. An unheated basement or root cellar is ideal.
Spot-check the tubers each month. Remove any pieces that have rotted and re-wrap in clean newspaper before putting them away again. If the tubers seem to be shriveling, you either didn’t allow the skin to form, or the area in which you are storing them is too warm.
In late March/early April you can move the tubers into a warmer area to help bring their eyes to the surface. After you’ve finished dividing them, don’t be surprised if you have many more tubers than you have ground to plant. Give them to your friends to enjoy or give them to the Norwood Evening Garden Club for their spring flower sale. Remember, you only need one tuber with an eye to get a fabulous bush full of flowers. You don’t want to plant the entire clump; doing so weakens the stems.
Of course, if you think this is too much work, you can let the tubers rot in the ground over the winter and buy new plants or tubers in the spring. This could become an expensive proposition, however, if you’ve developed Dahlia Fever.
To learn more about the various ways to store and care for dahlias, visit the Colorado Dahlia Society’s website http://www.dahlias.net. It is the most comprehensive dahlia site on the Internet.
Donna Lane owns Lane Interiors & Gardens, is a master gardener, president of the Rhode Island Dahlia Society, past president of the Norwood Evening Garden Club, a member of the Garden Writers Association, and an active member of many other horticultural organizations. You can reach Donna at LaneInteriors@verizon.net.