purpleinopp said:That's colder than where I've lived before, but I think you could get started with Sempervivums (hens'n'chicks) and there's a few Sedums that I think are hardy that far north. Possibly some dwarf evergreens, but I don't get into those at all. A search here of specific characteristics for zone 5a, and clicking the "suitable for mini gardening" box yields 10 results.
As you find suitable plants that don't have the zone info already filled in here, it would be cool to help other gardeners out by adding that here. I've done that for the few that I've left outside that are still alive after a winter, but I can only say that they're hard to Z8b.
As others see this, hopefully, you'll get some other suggestions. Best luck!!
Pussytoes, mosses, chocolate chip ajuga, and Platt's Black Leptinella could possibly make it. I'm in zone 6a and they do well here. Since it is a mini garden you could design it to where you could place an aquarium upside-down over the entire mini garden. Also, proper drainage goes a long way when it comes to winter survival for plants, cold and wet kills. You could also consider planting known winter hardy woody-stemmed plants like a rose of Sharon and bind their roots like a bonsai. Use your imagination and go wild.
That border of bottles is quite the eye-catcher! Looks great!
