My final comment is don’t be too upset if you get NO media showing up. That might mean that you need to change your story idea, or even that some other major news broke that day, and your event was pushed further back in the priorities.
This points to another thing to consider: Know what is already scheduled in your community. If the rodeo, or a parade is scheduled for that weekend, your farm visit will be much lower on their priority list, especially if the newspaper or TV station has a small staff.
If possible, try to plan such farm visits at a time of the season when most visitors (and the press) are not already overwhelmed with other activities. Your chance of getting the media to attend, or even publish the event, are best at times when there are few other events happening in your locale.
Also, it is best to study the local media. If it is a newspaper, subscribing to that paper will give you a better feel for their 'flavor'. You will understand the types of things that catch their interest, thus assisting you in designing an event that will perk their interest. If there are dozens of 'Farm Tours' in your area, you will need to come up with a twist that makes yours sound more interesting than the rest of them.
In most small communities, family (and children) activities play an important role in attracting media interest.