I have planted a bunch of them from Lowes, they need plenty of moisture to sprout, once they finish blooming let them completely brown up and die, in early fall mow them down, in many cases you will get some to come back the following spring
Make sure you read the label some of the mixes contain some filler.Some wild flowers are bi-annuals and won't Bloom till the 2nd year. Once you get a good stand like Channey said let them turn completely brown before you mow down and you will have wild flowers for years to come..If you will clean up and till the area you want them the 1st year you will get a much better stand of wildflowers.
I already have a small stand going just looking for more seed to fill in the gaps and replace the annuals and others that have since disappeared over the years.
Wasn't sure if the store bought bags were worth anything or not.