To turn your garden into a long-term home for butterflies, you'll need to grow host plants on which their caterpillars can feed. Butterflies must have these plants to complete their life cycle.
Many species of butterflies have a single host plant. For instance, monarch butterfly caterpillars (Danaus plexippus) feed exclusively on milkweed (Asclepias spp.), a wildflower that provides a caterpillar with food and shelter until it forms a chrysalis, emerging two weeks later as a new butterfly.
So it is important to include a few host plants in your beds. For the most part, these will be native species that you may have already or can perhaps find in your neighbourhood. Be careful to prevent them from spreading too much, though, as some of these plants, including milkweed, are very invasive.