Large scale gardening exhibition and plant sale. Usually lots of unusual things on sale.
Held at the "Parco della Musica" Information on how to get there is at this web page in English, French and, of course, Italian:
http://www.auditorium.com/en/info/come-si-arrivaThe official event web page is:
http://www.festivaldelverdeedelpaesaggio.it/If you do come by public transport please be very careful of pickpockets who, as in every city, focus on strangers/tourists. Rome is not a violent city, no mugging as far as I know. Pickpockets are opportunists who will leave you alone if they see you are prepared. Bags never on your back or hanging loose from your shoulder, always in front of you zipped up with your hand over the clasp. Hand inside your pocket where your wallet is, front pocket, never back. Please don't think I am an alarmist or a nanny. I travel to work by metro every day and I intervene at least 3 times a week. Usually, but not always, children are the culprits. Pickpocketing is an enormous problem in Rome as it is undoubtedly in many cities throughout the world.