Mulch the heck out of them if you must keep them in the ground and pray for a mild winter. Otherwise, bite the bullet, dig them up, and, if it's going to freeze, then take the time to bring them into a protected environment until the cold passes.

It wouldn't help during a power outage unless you went to the extreme of delegating a generator for the cause, but the ThermoCube available at Home Depot or online is a wonderful gadget for preventing freeze in one's tuber storage area. A space heater plugged into one of those in an outlet in an enclosed area and you're almost guaranteed to prevent loss from freezing.

I got lucky with stored tubers during our 6+ day power outage and icy cold a couple winters ago, but every clump I left in the ground last year (duplicates or didn't-cares) was rotted to pulp this spring. I would dig up anything you don't want to repurchase and experiment leaving those you don't care so much about in the ground with a heavy mulch of leaves or straw.

Good luck. I'm waiting on the first frost of the year, either tonight or over the weekend and then it will be time to get the autumn digging underway. Ick.

We are expecting our frost this week and there are so many big buds out there. I am sure I will cry. I am going to cut off the tops and leave them in the ground a couple of weeks to see if I can bring up some eyes.

Hi Poochella,
Last year when I dug them up, I left the ones that I did not care about in the ground and sure enough they all came back... We generally have pretty mild winters and I can pick flowers for the stand until November, but like everywhere there is always the chance that it will get colder than usual. (Which it did last year).I just keep thinking how I nearly killed myself digging all those tubers last year....and how lovely and easy it was getting a nice package in the spring and just plopping them in! I have a VERY large maple tree by the flowers and I was hoping to cover all the rows with leaves....one thing to note I started all my plants in one gallon pots before putting them in the field ....so they are not planted very deep. I just really want to hear someone say "Leave them in Janice...They'll be fine" ...and it would help if they where telling the truth!

How about this: "Leave them in Janice...They might be fine." And that is the truth, but it's the 'might not' implied that you have to weigh for yourself. Zone 8 is better odds for survival than zone 7 anyway. We are supposed to have a milder, drier winter out here in WA this year, but we'll see.

Thanks Poochella. That's good enough for me. We have pretty mild weather here on Vancouver island and there is good drainage so I think I will take a chance....I know some varieties are not as hardy as others...but I only have one of each anyways....OK, I know, I can pretty-well convince myself of anything...I don't really mind the digging etc., but I think it was the disappointment in the spring that did me in(all those mushy tubers...with shiny metal name tags)I'll have to keep my fingers crossed!
Now if I could figure out what to do with those darn spider mites? Do they affect the tubers if the plant is infected so late in the season and not really showing any serious signs of destruction?

I've only had spider mites on a perennial, not a dahlia. See the article below for an exhaustive review of chemical mite combat. It mentions ripping out the entire plant but never specifies the tubers. My thinking is that they do not affect the tubers as they feed and reproduce their evil little selves on the leaf surfaces alone. But it also mentions a soil drench and overwintering females, so who knows.

Perhaps if you leave your tubers in the ground successfully, be on red alert for the first sign of mites next year and take corrective action to control them early.
Good luck. I'll cross my fingers for a mild winter for you while digging and dividing in the cold, wet slop we call early winter here.

Here is a link that might be useful: An article on spider mites.