Posted: 10/02/2014 at 19:29
I think if you have to keep them in pots it's important to make sure the pots are big enough to sustain them and you remove some of the old compost each year and replace it with fresh, as shrubs will use up the nutrients very quickly. Also, making sure they have adequate water but aren't waterlogged either, and they have suitable drainage. Plants in pots are always going to need more attention than they would in the open ground. Bringing them inside means they'll lack light too, which won't help.
Is it possible to post a pic, and is the balcony quite small Possum? If it's not over or under watering, it may be as simple as needing fewer shrubs in bigger pots so that they have room to grow, especially when you say you've had the same issue with other plants.