Paradoxically enough, despite being an Interior Designer, one of the most frequent matters that I am called to write about by journalists is to do with spicing up garden's and patios. Artwork is not usually found in gardens because the rain would wreck it and the sun (if we get any) would bleach it.
My initial comment to that school of thought is: 'so what'? A piece of art can be impermanent and its degeneration can also be part of the charm: watching it fall apart month after month is part of the fun (providing it isn't a Picasso which I wouldn't necessarily advise!). So, get some art on that patio, balcony and garden - view it getting scorched by the sun and drenched by the rain and embrace the imperfection of it all!