There is no one answer to "how do you store tubers?" There are many different methods and most of us dedicated dahlia growers have tried them all at one time or another. What complicates the issues isn't the method, many of which work just fine, but what is your situation regarding storage? Ideally do you have a nice cool place around 45-50F that is both dry and dark? Another is when you dig them and how you process them. Conventional wisdom says wait until the tops turn black with frost, then wait two weeks. This allows the tubers to develop a tough skin and also puts the plant on notice to start pumping energy to building the tuber up for the winter rather than toward plant and bloom. The timing can be a problem for some in warmer areas or those having unpredictable weather.
I know. That would be all of us. But some people have weather that gets cold, then warms up, then gets cold, and rains, then snows. You can see what I mean. We, here in Alaska, pretty much just get colder and colder then freeze solid, then snow.
From here it gets complicated. Some dig the tubers shake off the dirt, let them dry a few days and then store the entire clumps in cardboard boxes. Some dig, wash the dirt off thoroughly, let dry three or four days, then cut the tubers apart, each tuber with an eye. (another topic all of its own.) Then they are stored in peat, perlite, vermiculite, a lite mixture of all three, sawdust, you pick the media. The idea is to give the tubers something that can absorb excess moisture (so they don't rot) and yet prevent drying out and shriveling. That is where the saran method comes in. After drying, some wrap each individual tuber in saran. The idea is that the tuber is prevented from drying out (so very important to make sure they are quite dry), and if one rots it doesn't affect any others. Okay if you only have a few dozen, pretty difficult if you have a few hundred.
Some tubers will try to grow over the winter, some you can't even see an eye on. No clue why. For me, I take mine out of storage around the middle of March (a little early if your last frost date is May 31). For those sprouting, I pot them up. For the others I lay them in flats half into the soil (horizontal not vertical) and water lightly. When they sprout I pot them up. If they don't then I pitch them.
I am sure others will add to these comments which should help clarify any points I missed or didn't represent correctly. Good Luck.
