They need to be kept at a temperature of 21ºC (70ºF). Until early May before you begin the harden them off. This applies if you've grown them from seed yourself. If you've ordered Young Plants from us, we do all this for you so you'll receive a 'garden-ready' plant that can be planted straight outside when they arrive in late May.
During spring, plant Begonia Tubers in trays of moist compost. Check tubers before planting and make sure the concave side is uppermost, lightly cover the top of the tuber with a thin layer of compost.
Maintain a temperature of 16ºC (60ºF) in a bright position, water when the compost dries out. When shoots are 5cm-7.5cm (2in-3in) long transfer to permanent pots or hanging baskets.