I'm planning on putting Imperial Clover on the entire old garden spot by the house this Saturday (Sept 14) since there is a reasonable chance of rain in the forecast. I got the ground ready to go last weekend so all I have to do is broadcast the seed now. I figure it will help the soil and do double duty to feed deer. I don't care if I can't hunt over it as long as I'm helping feed the critters to make them healthier and keep 'em in the general area.
Any time in September is OK for clover.