Starting tuberous begonias
Ever had trouble getting overwintered tuberous begonias started? In late winter, lay the tubers in a flat or pot filled with peat moss or vermiculite. Be sure the upper surface of the tuber, where there’s a depression, like you see here, is facing up, and then barely cover with planting medium.
Place the flat or pot in an area that receives indirect light and stays around 70 degrees F. These tubers are very susceptible to rot so water lightly to keep the medium moist but not wet and don’t allow water to settle into the depression.
After about a month, roots will have formed and stems will be about an inch tall. At this point, repot the tubers into 6-inch pots filled with potting mix or their final containers and move the plants to a sunny window or under grow lights. Begin hardening off begonias two weeks before your average last frost date. Once nighttime temps stay in the 50s, you can leave them outside.