Adult butterflies need nectar as a food source and this is any flower that the adult butterfly can feed from using their proboscis. We call these plants nectar plants. Typically these are small tubular flowers such as daisies, verbena, buddleia, lantana etc.
For butterflies to breed they need food or host plants for the caterpillars. The adult female butterfly will only lay her eggs on a plant she knows her caterpillar will eat. Each butterfly species will only eat a specific plant or plant type, which could be selected grasses, sedges, pea flowering plants, bushes, mistletoes or trees.
Here are links to an overview of the relationship between butterflies and plants, and butterfly gardening and 6 steps to make your garden butterfly-friendly generally, but to learn more about what is best for your area, please read on.
Different plants are adapted to different soils. In many gardens the topsoil may have changed as fertilizers, compost, mulch and different soils are added, so shallow rooted plants not formerly in this area may grow.
The soil below, however, will not have changed and for deep rooted plants such as trees and shrubs to survive, you need to select plants that are suited to your soil and rainfall.
This is especially important in those areas in the West Beach area of the Adelaide plains where former swamp land are now housing developments. In these areas, the soils below can be quite saline.
So the first thing to do is to work out what plants grow well in your area. Then, select plants suited to the butterfly species that may breed in your garden if the right food plants for the caterpillars have been planted.