In the wild, as wildflowers bloom and ripen into seed all summer and into fall, the seed simply falls to the ground and is "planted". Of course, in general, Mother Nature has unlimited wildflower seeds to sow. In the wild all kinds of things happen; Seed falls on rocks, on other plants, etc., and never reaches the soil. This is the price a wild-sown seed pays, and billions are lost each fall.
When a wildflower gardener tries to emulate this process, we do all we can to "help nature along." That means, we clear the area, open the ground, provide good seed-to-soil contact for every seed, water if necessary, and do anything else to assure our seeding's success. It's easy and the work is the same as required for a spring planting. In fact, some people think fall planting is easier.
Like fall-seeded lawns, fall-planted wildflower seed has a chance to "settle" into your site during the winter, and is ready to burst into growth in early spring. This is why fall-planted wildflower seed is up and in bloom about two weeks earlier than spring-planted seed.
Every fall-planting advocate mentions it. In the fall, the gardener has far more time to get work done for two reasons. First of all, there is a longer period and far more "good days" for planting in the fall than during the tricky weather in spring. Secondly, the gardener always has more time during the fall than during the spring rush to get everything done after winter. (Many wildgardeners combine wildflower seed planting with fall bulb planting, and that's always a good idea. The times for both are identical.)
Fall planting is done after your growing season has ended. That means any weed seed in your soil is dormant, unlike in spring when it's highly energized and bursting to grow.
This dormant situation is a real help to the gardener. For example, if you clear your seeding site one weekend, and don't plant your wildflower seed until the next, that's fine in the fall, and not OK in the spring. Obviously, with the weed seed dormant, you can take your time. But in spring, it's necessary to clear and seed on the same day, because if you don't, the weed seeds (they're in ALL soil) have a jump on the wildflower seed you're about to put down to compete with them.
With a fall planting, the weeds that do grow up in your flowers are easily removed when they appear as small plants along with your wildflower seedlings in spring.