Tossing seeds onto snow might result in an instant bird feeding frenzy rather than a naturalized garden come spring. Some seeds, including many native wildflower seeds, need a moist chilling period (below 45°F for about 60 to 90 days) to break dormancy. The process is called cold stratification, and it can be done several ways, including sowing seed outside into beds in autumn, planting flats of seeds in coldframes, and chilling seeds in the refrigerator.
"Broadcasting seeds on snow could work, but I don't see any real point in it," says William Cullina, author and nursery director of the New England Wild Flower Society. "You'd have better luck preparing a site in fall, before the first snow, and sowing the seeds then." Wildflowers often grow in poor soils and difficult climates, but they still benefit from a well-prepared seedbed. A raised bed filled with high-quality topsoil provides the best environment, but a garden bed with well-draining, fine-textured soil will work fine, too. In either situation, dig in 1 to 2 inches of finished compost before sowing.
Cullina suggests sowing rows of seeds in late fall and covering the seeds very lightly with soil or hay. "In spring, you'll see the seedlings come up in rows, and then you can thin them and transplant them." This method produces successful results with minimal hassle. Columbine (Aquilegia spp.), blue stars (Amsonia spp.), and members of the aster family (Asteraceae), including Joe Pye weed (Eupatorium spp.) and blazing star (Liatris spp.), generally germinate well with this method, Cullina says. I recommend that you also contact a local wildflower organization and ask about wildflowers that grow well from seed in your area (try the McHenry County Defenders Wildflower Preservation and Propagation Committee; 815-338-0393, mcdef.org).
If you'd like to try the other cold stratification methods mentioned above, I encourage you to read Cullina's book The New England Wild Flower Society Guide to Growing and Propagating Wildflowers of the United States and Canada (Houghton Mifflin, 2000). With several detailed propagation techniques and profiles of a vast array of native wildflowers, it's a wonderful resource for anyone interested in dipping their toe (or entire self) into the sea of wildflower propagation.