Somewhere over half the balconies here in Barcelona have houseplants on them, and about 1 in 10 are covered at least halfway. A couple balconies look like mini jungles. I’m not surprised, the city smells like car exhaust and cigarettes, typical for a big city. Also, Spain has a good climate for cacti, so lots of people have either desert or jungle cacti on their balconies. Even entire small trees in pots. Or not-so-small trees, I’ve seen multiple pots that must have been three feet across on some larger balconies. Plants all over the insides, too.