As a rule, Begonias need some sunlight, but they don't do well if that sunlight is harsh and direct. Instead, place them in filtered light, such as beneath high, thin tree canopies or on a porch. However, some begonia varieties might tolerate more sun than others. If the soil is dry when you put your index finger 1-2 inches until your top knuckle into the soil and it feels dry, then you need to water your Begonia. Feeding Once a week apply half strength (1/2 T Miracle Grow or other soluble plant food per gallon) fertilizer solution in place of regular watering, being sure to give the basket enough so that liquid seeps from the bottom of the pot. Tuberous begonias are not heavy feeders, so don't overdo it.