Something that hasn't been mentioned is how the balcony material itself can play a role (like, if it's sealed concrete versus porous stone). @sean_lane98's point about rocks trapping moisture made me realize that even with lifters, if the surface doesn't breathe, you're just moving the problem. I've used leftover ceramic tile spacers (the little crosses from DIY projects) because they're rigid, allow gaps, and won't decay. They're often free if you have them lying around, and they handle weight without compressing. Plus, they keep the pot level, which corks sometimes fail at if they're uneven.