When can I plant tuberous begonias outdoors?

Question:

When can I plant tuberous begonias outdoors?

Answer:

Plant tuberous begonias outdoors after the danger of frost is past. In central Iowa, mid-May is an appropriate planting date.  

Plants started indoors or purchased at a greenhouse should be hardened outdoors 7 to 10 days before planting.  Initially, place the plants in a shady, protected location.  The tuberous begonia foliage will burn if immediately placed in direct sun.  Strong winds can easily tear the foliage or break the brittle stems.  During the hardening procedure, gradually expose the plants to longer periods of sun and wind. 

More information can be found in this article: Planting and Caring for Tender Perennials.