At my old house I had this one flowerbed where I would plunk tropical houseplants down into the mulch around some normal shade loving bushes. Most of the time I only had so much space to rescue some of these guys before winter set in. There were two normally tropical houseplants that survived for more than one winter under the mulch for me - one was Swedish Ivy and the other was a small leaved waxy Philodendron.

I don't know if the red calibrachoa is a hybrid or not but it's the only color calibrachoa I know that lives to return so long as it is in slightly elevated area and not drowned in the winter.
Regular begonias and well sited fancy geraniums will return for me if they are in a well drained sunny spot. Not often though.

Last year I planted bunch of dianthus and snapdragon both were label as annuals so I put some on the front yard and ont the backyard and I was too lazy to pull out the ones on the backyard; early in the season they start coming back to life and now they are full of blooms,my neighboor woldn't belive me until I show her the rough old wood under the new growth,by the way dianthus stay ever green.

itzy, both annual dianthus and annual snaps are so- so perennials here- coming back for me as many as 4 years running. You lose about 1/3 to half the plants each year. A lot of so called cool weather annuals are like that, but some peter out in the summer. The annual mealy cup sage does the same (victoria, blue bedder)- comes back 3 or 4 yrs. Dottie, i've had the red callibrochia come back, but 1 winter for me. Never was brave enough to try any but hardy begonias and i don't grow the regular geraniums to try. Bachelor buttons love the winter- it's the summer they don't normally survive. In fact, i seed them in the fall along with nigella, larkspur and poppies. I've seen john's miracle bed and it was amazing what he could nurse through.

Couple things i've had survive that weren't supposed to be hardy are stevia and lemon verbena. I've heard of others who have had both survive, too.

tam,
I wish you could post for me a photo of stevia seedlings.
I know I must have pulled out plenty in weeding but I don't recall the original plant appearance and seedlings often don't resemble the mature plant.
Surely am not going to taste all the weeds I pull!LOL

I was weeding this past week before it got hot and suddenly noticed a stank . Cilantro.
Now I hate/detest cilantro and there's no way I would have planted it. How did it get in my garden?
Friends said someone must have brought me a salsa for a party and I put the remains in my composter but chopped leaves of cilantro aren't seeds??

Oh dear..I think I just found the answer.
Cleaning out my old spice rack I dumped 8 year old spice seeds on the ground under my bird feeder for the doves and seed eaters.

Coriander.

I done done it to myself..mystery solved.

I had a dianthus in a pot that made it through winter before last in days of subfreezing ...but it barely made it through this last winter (which was milder). I had decided maybe it likes to be frozen

Stevia, geraniums, and begonias here.

We have lots of spider plant babies at work and I like to pop them all around in my dry shade area. Every year I am surprised when they come back ha.

Dottie, stevia hasn't reseeded for me, though it did bloom a bunch one year and i collected seed. I never tried to raise any from it. I suspect it doesn't set a whole lot of viable seed, b/c when you order seed you get a couple, not lots. The one i had was truly perennial, coming back about 5 years. But it diminished a bit and came back later each year. Finally stopped a few years back. I've been taking a pot into the basement each fall that goes dormant and comes back in spring. It looks just like it does when you buy it- look at it next time you're in a nursery. Pretty unassuming, really.

Funny story about the cilantro. I love the stuff but it does get a stank to it once it begins to bloom.

Adele, at the fairgounds they had spider plants in the ground in one spot and i was surprised. Erv said they'd been perennial. Never would have guessed.

I have setcresea overwinter (2 yrs.) here in Alexandria, Va for me (I'm originally from NC, that's why I'm reading this) & my rosemary can't be killed-I had one that bloomed for 7 months, starting in Feb.!?

Setcresea is amazing stuff so long as you put it where it can spread and you don't plan to move it.

It is the one plant besides lambs ears that tolerates being under a black walnut tree,doesn't get any notice by deer or rabbits and seems to like being watered by the dog.

It makes a very dense root system to get the water it needs.