Farmer's markets provide a direct source of (usually) organically grown local fruits & vegetables allowing you to get produce that is generally less expensive and fresher than what you'll find in chain grocers.

Pittsburgh is blessed with a long farmers market season that runs from early May until late November and spans multiple locations across the city.  The CityParks farmer's market provides a rotating circuit of 7 locations based upon a weekly schedule.  The CityParks farmer's market does not seem to have any rules about vendor farming methods so you're likely to see a mix of conventional and organic produce, sold by either the farmer or a reseller.

CityParks Circuit:

For up to date information on dates/hours by location, please check the official CityParks website.

Locations Map

Here's a nice video from last season.