Answer: Seeding a wildflower mix is always a bit of a gamble, because some plants will thrive and others will fade away depending on the soil and other growing conditions. Annuals may self seed from year to year if they are well suited to the location. Perennials may take hold, and will colonize the area if they are well suited to it. (In my experience it is often more successful to set out small perennial plants and care for them until established than to try them from seed.) In the meantime, you will probably need to be proactive in terms of weed control and discouraging more aggressive interlopers. You might also want to become as familiar as possible with area natives so that you can recognize them if they pop up. As far as what to plant, you could try a broad range and see what "takes" or you could talk to local naturalists and ask them what would typically grow there -- I would suggest talking to people who are familiar with the local area. In addition to moisture levels and sun and wind exposure, you will also need to consider soil type to make a best prediction. Since many flowers bloom only seasonally, you might be surprised to find that there are already many wildflowers present -- particularly in the existing soil seedbank. It is also worth keeping in mind that what is a weed in one person's eye may be a wildflower in another's view.
Have fun with your project -- you will have many years of enjoyment!
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