winterizing on a fire escape

hey guys. i'm new to the forum and only a few years in with bonsai. i have a question regarding winterizing (proper term?) my plants. i live in NYC on the 5th floor, and my back yard is a fire escape! a terrible place to grow bonsai, but much needed in such an urban environment. the wind chill gets well below -20F, and its 5 stories above ground. i should also mention that i live in an old building with no thermostat, so in the winter the heat is just ON. point being, my windows are open all winter. seriously. otherwise my apt is like an oven. i have window shelves for my plants as of recent. will the plants that i have that require a winter (maples, pine, cedar, etc) be given a suitable winter on such a shelf at a partially open window? or should i devise something for the fire escape. due to the city environment my plants are all in small pots, but i have a few to many to put in the fridge for 2-3 months.
anybody with any experience in such conditions or similar? cold winter, small spaces, above ground?
any input would be very helpful. thanks!

c.ferd wrote:winterizing (proper term?)

Wintering.
Some pics might help us see what type of space you have. Maybe a cardboard box with a foggy piece of plastic taped to the top???

If the windows are open maybe you could put them in box on a box with some mulch and have it next to the window. The box in the bottom would be open to allow heat to keep the roots from freezing to the point of damage. See the drawing below. The text is a little hard to read, that lower text says "open space to capture some heat (venting probably needed to regulate temp)"
The other issue with this would be the fact that it would be against fire code?

I like Jim's clever apparatus, if you can do it.

Otherwise, I'd take some pond baskets or milk crates and pour in mulch, place the trees in, and add more mulch to the tops of the pots. When it gets below freezing add more mulch to cover most of the trunks. When it gets down to below the hardiness limit of a particular variety then bring it into the apartment and keep it in front of the open window until it gets warmer.

Is an aquarium tank a stupid suggestion? A friend of mine over-winters his on his balcony in one of these. I'm not sure he gets temperatures below about -7 Celsius, but he does get pretty strong and cold winds. (He's on the 7th floor) You could put mulch or gravel on the bottom (my friend uses those polystyrene chippings you get to protect items in parcels) and it could go either on the escape or at the window. The benefit is it lets in light as well as providing a bit of shelter. It's not far removed from Jim's design as I am seeing it.

Don't forget to remove the fish tho'!