The arrival of the Carro Matto to Florence occurs on the last Saturday in September. It is a part of the celebrations of the "Bacco Artigiano" that take place to celebrate the end of the grape harvest in the Chianti Rufina region.
It used to be on September 29 to celebrate St. Michael's but now just takes place on the last Saturday of the month, hopefully you'll be here around that time since it is an incredible display!