I borrowed the ebook of Grow Cook Eat by Willi Galloway from the public library. So far the most useful factoid is that mustard green seeds can be planted when the soil temperature reaches 45°F. According to Oklahoma Mesonet we are there now. In the fall, the book says to plant when temperatures stay in the 70s in daytime. I assume that means air temperature. That may be a little harder but we can try!