Answer: It sounds like your seedlings got sunburned. Just like people, plants that haven't been acclimated to outdoor conditions suffer from exposure to the elements. Hardening off plants is the process of gradually getting them used to a change of environment. For seedlings, I recommend taking anywhere from a 5 to 7 days. Start by putting your seedlings in a spot outdoors in dappled shade and out of strong wind, and bring them back inside after a few hours, or when you get home at the end of your day. The next day, put them in a slightly more exposed area. After a few days of gradually increased exposure, leave them out overnight (unless a frost is likely). By the end of the process, they should be able to withstand the conditions they'll face in the garden.
Bush beans, unlike tomatoes and peppers, mature quickly enough that you don't have to start them indoors. They actually fare much better when you sow seed right where you want the plants to grow. In general, transplanting bean, pea, or corn seedling from indoors to the garden can set them back enough that you don't gain any time over planting seed. If you are in part of Minnesota that has less than a 90 day growing season, you can still plant beans varieties that mature in 60 days or less -- and plant two batches, the second a couple of weeks after the first sowing -- to extend your harvest.
There's lots of information at the National Gardening.com Web site to help you with understanding soil, plants, seedstarting, and more -- please visit and take a look at the great resources available -- we want to help you succeed!
Hope this helps!
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