Here is a little video that we made doing our food plot. We planted it about mid august and have not gotten any rain since so we are hoping it will all grow. Feel free to let me know what you think, im always open to anything i can improve on. https://vimeo.com/73739493
It depends on the region you are in and it also depends what you are planting, that will regulate when to put it in. I am no expert but i would say in the midwest no later than the beginning maybe even mid september but we put ours in mid august usually and that seems to be good. Last year during the really bad drought we put it in the second of september and it grew well also.
It has only rained like an eighth of an inch here so nothing and it has been really hot. I'm hoping it will grow at all