Unlike my neighbor who grows dozens, I'm not a huge dahlia fan and only grow a couple of the dark (purple/black)leaved varieties. Our ground doesn't usually freeze so I don't lift them, leave them to fend for themselves in winter. If they make it, they start to sprout in May, sometimes late May, slow to wake up.

If we do have a freeze where too cold temps go as deep as the tubers in the ground, they turn to mush and are gone. The soil in above ground pots will freeze in warmer temps than my ground will freeze, I don't think there would be any benefit to dahlia tubers above ground outside. 8b here, and I lost Bednall Beauty to temps in the teens (ground, with fir branches crisscrossed over them for added protection) a year ago.

I wasn't thinking about putting them out in freezing temps, and I know containers freeze a lot faster than the ground, but guess I was hoping there would be some window of time where the greenhouse effect of the container would push me up a zone or two. But probably the window of time would be around the same time I would be putting them in the ground . . .

Mainly I think I was thinking, all my indoor room this year is already used up! Suppose some wishful thinking was driving me.

WS your dahlia tubers would be no different than leaving them in the ground to winter over. Soil will freeze, the tubers will freeze in the containers, same as soil and that will destroy the tubers.

Dahlia tubers are not freeze hardy and will not survive the freeze/thaw cycle that winters bring.

If per chance you got lucky and they survived a short period of freezing temps and frozen soil, any snow covering them, will provide far to much water content and it will rot the tuber.

What you can do, is pot the tubers up that you saved over the winter in some potting mix, I use miracle grow potting mix and put them outside come about mid April to the first week in May.
Cover them as if you where WS the containers and put them in partial sun.

By June, they will have good growth on them and you can move them to larger containers or plant them in the ground.

I did this with mine for the past couple of years, but didn't put them out till around May 1st as we had horrible flooding rains and they would have gotten far too wet.

All 40 tubers grew beautifully, didn't expect to have all of them survive and grow, so gave quite a few of them away.

But, like I said, putting them out in the winter "Winter sowing them" is no different than leaving them in the ground for the winter. The won't survive the freeze thaw cycle and the snow, snow melt on them.

Fran

My question to you, then, do you think putting them in a deeper pot with a cover helps keep them from rotting rather than putting them in say a gallon jug and in part shade? or is there a difference as long as night temps are staying above freezing?

This is all helpful info, because I have not saved my tubers before I have just grown them from seed . . .

Perhaps I'll try a few in jugs (ones I don't mind losing), if we are having good weather in April, as an experiment for myself, but I have a feeling I'll probably be too busy with so many other gardening chores by then.

I have so many alocasias, colocasias, brugmansia, etc. to deal with getting an early start and moving from inside to out, that adding dahlias to the list seems too much.
Think I'll put them directly in the ground when it's time!

Thanks to everyone for their input . .