It seems that most of the comments on the Lake Constance area here are about the summer. That's not an option for us. Can anyone comment on October? I did check Mainau Island and it seems to be dahlia time in the garden there. Are there likely still flower lined lakeside promenades, or is their season over? Thanks all.
If nobody is answering this very specific question I recommend to look at photos and videos from the destination in different sources. In Google Maps very often the date is shown when the photo or video was originally taken.
Contacting the local tourist info is also a good idea. At this occasion I would specify the date as much as possbible because the conditions at begin and end of October are very different at many places.
A few years ago, I visited Mainau Island on October 4. It was a bit rainy, but the flowers were amazing.
The climate around Bodensee (Lake Constance) is very mild, at least compared to the climate of Germany. There are even palm trees on the lakeside promenade in Überlingen. So there shouldn't be any problems seeing myriads of flowers in October. The chance of an early frost is very unlikely.
Thank you all so much!