Welcome to ATP.
Roses simply are not indoor plants, even when they are placed in front of a window that gets a lot of sun. The intensity of light of the winter sun is less than in other seasons and will not provide the plant with enough light to serve its needs.
I do know people who have successfully over wintered roses indoors, but they had to use grow lights to provide sufficient light for the plants.
The bigger issue is that hot and dry conditions are perfect for a spider mite infestation. Spider mites are one of the biggest problems in commercial greenhouses, so every plant they produce has the potential for an infestation. The people I know who have grown their roses inside wash the plants every other day to avoid an infestation. That's a lot of work.
Keeping your rose outside is really your best option. You might want to place it on the inside portion of your balcony, so that it can get some heat through the walls of your apartment. You do want to make sure that the plant does not dry out.
In the US, all minis are own root plants, but I have heard that in some countries the miniature roses are budded. If your plant is own root, it has a better chance of survival under the conditions you describe in your post. You might lose all of the top growth, but if the roots are still alive, your plant will come back. This is true even if the soil around the rose is frozen. Of course, it depends on the rose.
Studies have shown that roses will even continue to grow roots and come back with temps as low as -15F. Your -25C is about -13F. I would probably try a heat mat under the rose if temps dropped that low. At -10C, you are probably OK. That is +14F, so it is not quite as close to the borderline.
Insulating the plant is really a great way to go. It will provide a more consistent soil temperature between the day temps and night temps, which will avoid some of the stress created by fluctuating temperatures.
Photosynthesis slows down at +70F, +21C, which signals the rose to go dormant. If it is a repeat blooming rose, it will never go completely dormant because the genes which were introduced into the rose gene pool for repeat bloom also brought along the inability to go truly dormant. However, all cellular activity will slow down.
Since I have never grown roses in such a cold climate, what I am sharing with you in this post is "theory" based upon what I have studied about roses and has not been tested by me.
Good luck with your rose.
Smiles,
Lyn
