I have a couple red twig dogwoods and they do quite well during winter and are a nice 4-season shrub. They do grow fast though, so at some point, be prepared to prune and/or pot up to a larger container.

There are many cold-hardy ferns that should do fine and you could check on the Bamboo forum for some recommendations of bamboo.

Feel free to scan through previous posts on the forum to get some ideas of plants that you can try!

I'm struggling with the same sorts of questions you are. The winter freeze-thaw cycle is the biggest problem for balconies. I'm west facing and fairly protected balcony but my mugo pine didn't make it through this winter. Many have tried to discourage my hunt for hardy shrubs/small trees and suggested I just stick to annuals.

However, others more knowledgable than me have agreed that dogwood might survive winter. I also experimented with a boxwood this past winter and he appears to be alive & well. This year I'm going to try an Alberta Spruce, and probably a hardy juniper.

They say that when selecting shrubs for balconies, choose ones that are rated for at least 2 zones colder than the one you're in. And basically the containers have to be as big as you can possibly make them.

As for small trees, Lilacs are very hardy and the fragrance is a plus. Again, you'd have to have a pretty large container for it. That generates issues of weight and presumably having to move it one day without needing to hire a crane operator!

I'm not sure whether you're in southern Ontario but Vineland Nurseries, down towards Niagara, specialize in dwarf shrubs and trees, you might want to check them out. I believe they have a website and could ship plants to you.

'Hope that helps. Let me know how it goes,
Christina