Mid September is always a little bit of an awkward transition. You start seeing the "pumpkin everything" trend creep in but you're just not quite there yet.
Below is a recent mock up in my studio for an early September 2018 bride who loves the fall but leans more towards the earthy tones / isn't a big "flower person" + not into the pumpkin theme.
Rest assured, just because it's September - it doesn't mean you have to go full on fall. Stay true to what style you love instead of what season it is!
happy planning - molly