What zone are you in?
I would like to know how do you overwinter plants in compost pile...and why some don't make it?

I am in zone 5b (USDA says 6a, but we hit temps below -10 every winter the past several years).

I simply bury the pots in the compost pile, and make sure the plant is covered.

Some don't survive I suppose because that is too moist, or the protection isn't adequate.

I agree with Rina. An attached unheated garage is a great place, too. Just toss some snow on top of the soil from time to time (I usually water plants in the garage monthly, but that varies by plant type and container size). I over-winter about 125 potted plants in the garage on a makeshift OSB table on sawhorses. Works very well, unless someone near/dear to you forgets to close the garage door on a -12* night. Do you sense that last offering was born of personal experience? ;-)

You can even prevent that from happening if you cover the plants with an overturned box, which will capture the geo-heat that rises through the garage floor.

Al

Thanks to both of you for the tips. The window wells are dry and covered, actually above ground level (the main ground) but surrounded and insulated by raised beds contained by short dry stack stone walls. So I thought that might be better than the garage (which is attached and unheated, but I lost everything the one year that I tried overwintering in there -- Also I don't have room for much there, it is a 1941 single car garage!)

Wow, Al, 125 plants?! Definitely a bigger garage than mine!

Maybe I will try putting some things in a box, packed with wood shavings, in the garage.

Rina, I've seen some local nurseries keep their potted stock over the winter in beds of gravel (the pots are sunk into the gravel). That must be for good drainage as well as insulation from the rock.

I agree that gravel provides very good drainage.

I 'killed' a fig tree while over-wintering in garage by forgetting it to water whole winter - the cold didn't do it, total dryness did. Is that what possibly happened to your plants too?

Al is also in pretty cold area, and his plants survive the winter in unheated garage.

What perennials are you most concerned about?

Rina

I've got a couple of small roses and a hydrangea that concern me the most. I know that the figs will be fine, once dormant, in my basement (for the past 4 years I haven't watered them until they start to leaf out in March), and the viburnums should be fine in the compost pile. Also a hardy hibiscus -- that is one that I've lost before.

The problem with my garage might just have been the construction -- not at all insulated, thin walls. And if I recall, it was one of our colder winters. Things might have been fine with just a bit more protection but I don't know.

Some hydrangeas are less hardy, so I understand your concern.

Typically, it is recommended that plants hardy about 2 zones less would overwinter in containers without any problems. My experience is that as long as I keep them in well draining mix, somehow sheltered from the winds and in not too sunny spot, they survive better.

I has success with plants being grouped together, in dappled light, good drainage and covered/mulched with fallen leaves. Plants rated z5 survive. I don't have hardy hibiscus.

Rina

Rina, I appreciate your information, thanks!