The Missouri Botanical Gardens is a true gem in our area and provides a variety of science, conservation, education and horticultural advice. It is considered one of the top three botanical gardens in the world! Labor day weekend is the Japanese Festival; you won't want to miss it!
http://www.missouribotanicalgarden.org/
http://events.missouribotanicalgarden.org/Japanese_Festival
Labor Day: This isn't about BBQ, parades, sales, bargains, etc. It is a celebration of workers and the history of how working conditions changed during the industrial revolution.