Maybe, but you'd be taking a chance. Also depends on what roses you plant. I would think only the very hardiest, and even then, it's iffy. The problem is that no matter what kind of protection you provide them above the soil level, their roots are pretty much exposed to the freezing cold seeing as they are above ground. When roses are in the ground, their roots are in a zone where it is a bit warmer than the air temp and they are insulated. In a container of any type, the soil is going to freeze solid and stay frozen, probably damaging or killing the roots.

I too am always running out of room and have planted a few roses in large containers. They are lightweight faux terra cotta or faux stone so they can be moved indoors into my attached garage for the winter. They are still heavy filled with soil but manageable enough my husband can lift them. Maybe you can have the roses potted up in moveable containers instead of the troughs and move them inside into the room under the garage.

I suggest you build a trial raised bed for one or two roses. Line the sides inside with 2" Styrofoam. This'll act as permanent insulation from side freezing. Depending on the depth of the beds you'll still get freezing from the surface. Unless you plan on removing them for winter, buy only own root hardy varieties and avoid hybrid teas.
Were it me trying this, I'd use the foam insulation inside and build boxes over the beds for winter. If done properly and planned for when building the raised beds, the boxes could be easily assembled each fall.
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The boxes pictured are not built over raised beds but they could easily be.

Hello Montana_rose,

Being a zone 3 gardener myself, I'd say it's gonna be a whole lot of effort to have those roses make it through. They'd need to be covered with very heavy protection and still this would be iffy at best. Karl gives good advice, though when it's bitterly cold, some additional heat source would likely also be required, such as a string of incandescent lights turned on when temps plummet. It also depends if you live in a high snowfall area, as snow heaped over would really help. If you're willing to do the work, it just might be possible, though you'll need to go to great lengths and be keeping your fingers crossed.

I have no problem growing tender hybrid teas and floribundas in zone 3, though of course in the ground. Most of these are situated along the south side of my house and have their grafts planted about 4 inches below grade. Snow cover is rather reliable here and also much is blown off the roof and collects in that particular location, they're all snug under about 2 ft of snow at this time :)

Terry

Thank you all for your responses. I really appreciate it. Unfortunately, all your responses seem to back up my original worry that this probably is not the best use of my resources. We get really cold, but not a lot of assured snow cover. I think I'll just buy a bunch of pots so I can move them into the dungeon. Thanks again. It is very nice to be able to run questionable ideas by experts!

I think it would be easier and wiser to cram as many potted roses within that "dungeon" than to put such a tremendous amount of work into what might be a futile task attempting to winter them outside. I have an unheated well insulated attached garage that has been ideal for keeping over potted roses and other specimens. The coldest temperature recorded in the garage was + 21 F when the overnight outdoor temp had plummeted to a bitterly cold -40 F ... so, the garage has served them well and no damage has been sustained.