How best to over-winter container-grown fruit trees?

I have three dwarf fruit trees I planted as bare-root trees this spring in 20 gallon "dirt pot" fabric containers. They are cold-hardy varieties, but I know the trees won't survive the winter if I just leave the containers outside. Our winter-time temps get down to about 20 degrees in the daytime (occasionally colder), and 10-15 degrees at night. If I wait until the trees are fully dormant and then drag the containers into our basement garage, will they survive there? The garage gets down to about 35-40 degrees but doesn't freeze. However, very little daylight filters in, because the garage only has two tiny windows. We don't have an enclosed porch, so that's not an option. Any thoughts or suggestions?

Most fruit trees require a certain number of hours below a certain temperature. Do some research and find out what this is. If your plants actually MUST be exposed to a certain level of cold for X number of hours, then make sure they are going to get that. (I have an apricot that is supposed to be for a much colder zone and it has never fruited- not enough winter chill). This applies to plants in the ground, where the roots are insulated from a lot of the cold.

Other than that, the basement garage sounds like the best option. Almost freezing should keep them dormant without the risk of getting too cold. I do not think the lack of light would be a problem when they are fully dormant.
If the weather is getting a little variable while they still have leaves then I would wrap the container that holds the roots and perhaps look into wrapping the lower trunk, protect the graft as the temperature goes up and down.
When it is time to bring them back out, do the same. Protect the roots and the graft from sudden chills. They will need exposure to light then.

If they will ultimately be planted in the ground, then you can drape plastic sheeting over them, and even add some Christmas lights to keep them just a couple of degrees warmer. This works great when the difference is just a few degrees, but is probably not going to be enough to keep a container plant warm. The whole root zone can get a lot colder when the plant is in a container of any sort.

You could either heel-in the containers outside (probably preferable), or use your garage as you've suggested. Complete darkness would be better, though, as any light can stimulate plants to start leafing out early.

Hi RevMinnow,
Check out this site. It says to put the pots in shaded area first to keep leaves from falling. Then place inside near a southern western window if possible.
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http://www.pallensmith.com/index.php?id=36

This advice is intended for citrus trees to acclimatize them to indoor conditions. If you follow it for species that are supposed to be winter-dormant (as your hardy fruit trees are), they will not stay dormant - they'll leaf out again. Your trees will need darkness and cool conditions to stay dormant.

It would be nice to know what species and varieties we are talking about. Most cold hardy trees will handle sub 0F temperatures. My biggest concern for them would be drying out and temperature cycling. If they are left in the sun I think they are going to freeze and thaw over the winter instead of staying at a relatively constant temperature in the ground. I'd put them in sheltered shade somewhere outside, cover the "pot" with mulch and forget about it until spring. As spring approached I think I'd put them on the north side of the house so that they didn't come out of dormancy too soon and get hit with a late frost.