We also have a Greenhouse and 2 farmers markets.  

what I would recommend is setting up multiple locations.  that way you are able to track how each market does independently.  When setting them up you can tell it to copy all the items from your current location to the new one and then change the prices.

Now comes a bit of a complication.  You have to sign each iPad out and into the location you want to be using at the specified market.  What we do alleviate this is I run the Appstore version of Square signed into one location, and then I run the Beta version of Square signed into the other location.  Each is easily identifiable so there isn't any confusion.