I sprinkled radish, clover, rape, and wheat seeds yesterday before the rain. In Iowa, I liked to get my brassicas all planted in early July. G
Mid July is great time to plant brassicas.... wait until September in dry conditions and you got a recipe for disaster.
I plant my turnips the 1st week of september. Brassicas are a late season food source and a damn fine one. Give it a shot, planting it in sept. As long as your soil temps are conducive, you'll be fine.