Turnips are usually planted the end of July. Brassicas, which include turnips, have a 70-90 day maturing time. So back up at least 90 days from the date of your average first frost. I like to mix several brassicas together for my plantings. I like rape, turnips, and radishes at about 6# per acre. On my farm the deer kill the brassicas. I would almost say it is my best food source. That being said it is an aquired taste for deer. It often takes 2 years for deer to learn what they are and begin hitting them hard. The first hard frost converts a lot of sugar into the plants and that is when they really get after them. Turnips for me are good but not until late in the year.
Sorry, were kinda posting over each other here.
I just frost seeded my clover. I planted KOPU 2, jumbo ladino clover, and alice white clover. I got these from :
http://www.welterseed.com/productItems.aspx?id=2&org=0 I find the white clovers to be a little easier to maintain (clover needs mowed but not hayed occasionally)
My fall plots consist of: 1. Eagle brand soybeans, 2. brassica mix, 3. austrian winter peas (deer candy but won't last long) winter rye (not to be confused with rye grass) and winter wheat or oats mixed together.