For all locations inside Wisconsin, historical median frost date for the closest township is given to help with your decision. To take the field samples you can manually count measured rows of plants, or you can use you iPhone camera to automatically count plants. There is a help screen in the app that will get you started. It is as easy as holding your iPhone at arm's length and shoulder height out in front of you, with the camera facing down toward the plants at your feet. There are lines on the camera preview to show where the plant rows should line up. This app is free. Research for the Bean Cam app was conducted by agronomy specialist from the University of Wisconsin-Madison.