I would not worry. We have lots of liquidamber where I work. Some turn color faster than others, even though they are only 10 feet apart. There can be very minor variances in temperature and wind exposure that you don't even notice. With the difference in exposure that you describe I would find it odd if both trees acted exactly the same.

Thanks so much for you reply. I really appreciate it!

I had 6 western redbuds for 12 years, one will drop its leaves quickly and another right next to it will still have green leaves. Each of them was on its own schedule, even though they were right next to each other. Your description sounds normal for them. Once the leaves turned yellow they dropped quickly--the pretty gold was very brief.

Ginko will turn gold and hold for weeks and weeks and weeks--far better show, but a much larger tree as well.

Thanks hoovb!

Individual plants behave differently...think of two people in a room and one is warm and the other is cold...sounds like your C. occidentalis will be fine. They are not known for long periods of autumn color.

Thanks!