Some seed like clover surface broadcasts well under the right conditions. True frost seeding occurs when the top inch or so if soil freezes at night and thaws during the afternoons. This cause heaving and microfractures in the soil sucking the clover to a great level for germination.
The timing of the broadcast can affect your germination rates. There are risks associated with broadcasting on top of the snow. First, the clover seed becomes very visible for predation by song birds and the like at a time of year when many other food sources are covered by the snow. Another risk is a fast snow melt. This is of little issue on a flat field, but on slopes the seed can wash into channels leaving large bare spots and high density sections. Clover seed is pretty hard and will likely survive weather conditions but some percentage is lost as it sits over time without germinating.
In most cases, the result of broadcasting on top of snow is simple a somewhat lower germination rate because of predated seed. On the other hand, if you wait too late and soil heaving is over, while it may not technically be frost seeding, surface broadcasting clover can still be effective if weeds have not started.
My favorite use of frost seeding is not for establishing perennial clover. It is for filling in bare spots or thickening a thin or aging clover field. In my area, at least, I have less weed issues when I fall plant perennial clover with a nurse crop of WR. It gives it a bit more head-start than frost seeding does. First, some clover will germinate in the fall when it is planted. Second, the WR will help combat weeds while the clover is establishing itself.
Thanks,
Jack
