I look forward to enjoying the beautiful sights and having a picnic, a walk, and a relaxed bike ride in peaceful green surroundings when I go on the My Way Alpine tour in the middle of September.
Do the meadows, plants and trees in Salzburg, Vienna, and Switzerland turn brown from the heat of the summer or from the cold of the fall during September?
Neither. Everything is usually still green for the month. Summers aren't hot or dry enough in this area of Europe to parch the landscape. You might get just a hint of color change in late September, but the change over doesn't usually get underway until well into October.
Wait, slight correction. The Rhône Valley, which you would transit through to reach Zermatt, sits in a rain shadow between the Berner Oberland and the Pennine Alps. So, it's relatively dry compared to the rest of the country and could appear somewhat brownish-beige in September. Or not.
I wish we could share photos on here and I could show you my pictures from our 2010 trip - we were in Salzburg late Sept and even the public gardens looked amazing - lots of flowers and buzzing bees. And Switzerland in early Oct was as green as could be (Bern, Spiez/Murren and Zurich) - lovely temps, and lots of flowers still blooming in the city parks...
