When do you plant trailing begonias out in pots that you have over wintered?

You can plant trailing begonias out in pots after they have wintered in early to late Spring - depending on the zone. A rough rule of thumb is to wait until after the last frost or very cold night. If you have propagated the Begonias, then give them some time to get used to the cooler conditions by giving them a little shelter for a few days, such as on a porch,against a house wall or in a cold frame. If they have been indoor forced Begonias, then they may be a little more sensitive and need protection for a little longer: