I've had the best luck with a high nitrogen, low phosphate, moderate potash, timed release food, such as to Black Gold Multicote--there may be other similar brands available in Australia. They need a little phosphate to form bloom spikes, but too much makes them chlorotic, and they prefer a steady supply of nitrogen. Some brands of alfalfa meal will work, too, if you want to go organic, but you will need to apply it more often: say, once every two weeks in a container, or once a month in the ground.