You can create a mix of plants that bloom from early spring all the way into the fall. Selecting species that bloom at different times can ensure that you have flowers throughout the growing season. This can be done with only two or three species, or with many. The more species in the mix, the more variety you will have in flowers. Be aware that some wildflowers are annuals, some perennials and a few are biennials.
Annuals complete their life cycle in one season and die.
They are only replaced if they reseed themselves. Perennials will come back from the roots each year, and may also reseed, producing more plants. Biennials require two growing seasons to complete their life cycle and then die, but may reseed themselves. Selecting a location is as important as anything else. The most important consideration is sunlight.