There are a lot of things to consider in your planting dates. First, how susceptible are the seeds in your mix to the elements and the various critters that might consume them. If you're depending on a high content of soft seeds like Maximillian Sunflower, you may be better off waiting until post thaw. If your soil conditions or site happen to not be well drained and tends to be impassible in the spring, maybe the post dormancy/prefrost planting makes sense. I've had success with both using NWSG and hard-seeded forbs. Either way, I wouldn't push the early side of the planting window. You don't want the seeds to germinate before spring as they may freeze, frost heave, or desicate before establishing a good root system. If you're using a grass drill (banded disks), you should have excellent seed depth control. If there is a chance that much of your seed might be top seeded, you will want to make sure that your cover crop is adequate that your see doesn't blow away during a dry winter. The NRCS boys will be able to answer many of these questions pertinent to your site and the conditions it presents. Don't be afraid to involve an upland biologist or PF biologist to tailor your seed mix for the species you want it to favor. Having the variety of cover plantings you are planning, you may find you can really target some species with the main planting to improve the benefits of the others.
