If you've improved your soil before planting, you shouldn't need to use artificial fertilisers - except in cases where a plant is suffering a particular deficiency.
According to gardening expert Kevin Walsh, author of Water-saving Gardening, Water-wise Plants and Practices in Australia, using organic fertilisers like manure or compost is a better choice, as there's less chance that you'll over feed your plants.
Did you know that fertiliser use is related to water use? Using less water means you won't need as much fertiliser. And using less fertiliser means there's less chance of it leaching into our waterways and causing blue-green algae problems.
The best time to apply fertiliser is just before the start of the growing season. Make sure that you water the ground before spreading it around. You'll also need to water the ground again afterwards.
It's important to remember that Australian native plants are adapted to soils low in phosphorus. Applying too much high-phosphate fertiliser around them can damage or even kill them.