Fl IMHO Oct or late Sept after the summer rains have stopped is the best time to spread Mulch in our area. My reason is this gives the greater time frame where rain won't wash it a way. It also makes the property look best for our winner Snow Bird / Tourist season. As for Weed Control in summer. There are just going to be those places you have to Roundup every two weeks because of our heavy rains. However Round Extend or the less expensive Gly Extend I mix myself works great on those areas .