Mid-Atlantic here! Everything I read tells me I need to dig them up/store them for the winter, but mine overwinter just fine. Although sometimes they do fall prey to a squirrel or vole over the winter.

How cold/wet, do your winters get and for how long? I have some large flowered glads in a container, in an exposed position, that survived lows of 17F and are shooting up. They are in potting soil with good drainage, which may have saved them rotting in the torrential rain we had. Our winters can be very cold, but also short, usually dry but not this year.

Your soil matters too, if it’s heavy clay (like mine) they are more likely to rot in the ground. In saying that, dahlias mostly survive in the ground here with a protective mound of compost or straw. I have a couple of precious tender things that I plant in pots sunk into the ground that I lift and overwinter in the garage.

Our winters are very wet, and sometimes very cold, though usually for a short period of a few weeks with overnight lows in the upper teens and lower 20's and days that barely reach freezing. Though as I said that only lasts a few weeks. Soil has decent drainage, it's mostly topsoil with a good mix of organics.

I did read the other day that some Glads are hardier than others, though the article didn't name any varieties. Anyone have a good online source for them?

I have also only just begun to play with dahlias. Last year I dug them, stored and then panted them out and even with doing that only a few of the tubers produced any growth and fewer with flowers. This winter I did not dig the few that flowered and we'll see how that goes.

I live in the Willamette Valley (Z8B) and leave glads and dahlias in the ground over the winter. I do mulch everything in the backyard pretty heavily over the winter with the trimmings from our ornamental grasses. The dahlias, I divide in the spring (I find it easier then) and the glads I haven’t dug once in three years - they keep coming back fine. We have loamy/pebbly river bottom soil. Like @NollieSpainZ9, I am a faff-minimizer, or as my husband calls me: Darwin’s gardener.

Brian, as long as soil drainage is good, both dahlias and glads will overwinter very well in our climate.

Grief yes, they seem immortal, becoming absolutely vast when simply left alone. Although even a wet winter doesn't seem to make a great deal of difference in free draining soil (which, being both sandy and stony, mine is). Bulbs, corms and tubers are my garden mainstays here in my rain depleted part of the UK. Or massive gnarly roots (verbascums, malvaceae, baptisia, callirhoes agapanthus. hemerocallis, eryngiums, eremurus etc etc.).

I'll leave them in the ground this year. I will note that even though Pam and I live in the PNW, my little corner is a fair but colder for a bit longer as we are in the foothills. I have had dahlias rot in the past, though I do think that was due to bad soil. I am also more inclined to be a Darwinian gardener. :o) Thanks for everyone's thoughts.

“I am also more inclined to be a Darwinian gardener.”

I call it free range gardening, personally.

I've been off Gladiolus since my upbringing in Minnesota, where they were invariably planted in an absurd, multi-colored, wonky looking (because they never stood up) straight row, along one side of the veggie garden, and of course laboriously dug and stored for the winter.

Now, in the Willamette Valley Oregon, my neighbors have planted them in our heavy, wet clay and they've come back three years in a row. In one case they are becoming a bit weedy! Guess I'll have to try some myself.