Digging, Dividing, and Storing
Here in North Central Washington our dahlias need to be removed from the ground in order to save them and replant them in the spring. Tubers left in the ground will freeze and will die. We dig up our tubers starting in mid-October with the goal of keeping them in the ground for as long as possible to keep them happy, but not so long that they freeze beneath the ground.
Quality Tubers Keep Best
Tubers that know winter is coming will store better than those on plants still producing flowers. Sometimes we get a "killing frost" that turns the foliage black, but most of the time we cut our plants down to about 6" and let them sit in the ground for about a week before digging. This allows the tubers to harden off, and makes the eyes (next years stalks) easier to see when you divide.
Digging and Washing
The fun begins....
Sometime around Halloween, depending on the weather, it's time to dig. Loosen the soil 18" or so around the base of the plant then lift. We find a pitchfork works best to avoid damaging tubers. Be prepared to divide and store your dahlias within 24 hrs. Tubers left on concrete garage floors too long will feel soft, which means they are drying out. Think of a carrot left on the kitchen counter overnight. If you choose not to divide right away, putting clumps on a tarp or in garbage bags can buy you time.
Look for Eyes
One clump of tubers can be divided to produce many plants for the next year but not all varieties are equally generous come winter. One member reported getting 37 tubers off one plant, other varieties may only produce two or three. The key is to look for "eyes" and make sure each tuber has an "eye" which will produce the new stalk next year. In our sandy soil we generally get good tubers. There are many wonderful YouTube videos you can reference. Here is one...
There are many methods to storing tubers but the goal of each is the same. Keep them cool 40-45 degrees, and keep their moisture levels consistent. Too wet and they will rot, too dry and they will shrivel. Many of our members store theirs in moistened pine shavings from the farm and feed store placed into cardboard boxes lined with garbage bags inside like a lasagna, no tubers are touching. One rotten tuber will ruin the next. A styrofaom cooler works as well. Other members are saving space and wrapping theirs in plastic wrap to maintain consistent moisture levels. Either way, until a reliable system is created, checking on them a couple of times over winter can help rectify problems before they worsen. New Years and Valentines Day and easily remembered.