It is important that the tuber has sprouted before planting. These appear as small pink buds about September/October. To hasten sprouting place them in a warm dark place. Any tubers that are reluctant to sprout, try moistening them about twice a week. Once sprouted and to encourage early growth, place the tubers in a tray of good potting mix about 5cm apart with the tubers buried just below the surface. Begonias develop roots on the top and sides as well as the base of the tube. Unsprouted tubers can be left on top of the soil mix and buried later once they sprout.
Throughly water the tray but do not overwater. Keep the tray just moist but it is important not to allow the mix to become to wet. Only water the soil mix when it starts to dry out. Place it in a warm well light position, but not in direct hot sun. Once the tubers have grown and roots have developed they will require more frequent watering. Do not allow the plants to become spindly. Before planting out in the garden, after they have grown and once frost are over, harden the plants by placing them outside in a well sheltered position for a few days.
If they are to be grown in pots or baskets the tubers can be planted directly into the containers and then placed temporaily in a warm sheltered frost free area. Once the tubers are established then move them into their permanent position once the frosts are over. Do not over water until they are well established.
Begonias like a well drained soil and shelter from strong winds particularly the large flowered varities. They do not like a very hot position. The ideal is some partial shade during part of the day. Do not plant in dense shade as this will elongate the growth and also reduce the lenght of the flowering time.
When watering make sure the soil is properly moistened right down through the root system and then only water again when the surface of the soil had dried out. Do not over water or allow the soil to become to soggy. Also do not overhead water while the hot sun is on the plants as it can cause burning of the leaves.
Varities such as the compact Flamboyant types are more hardy and will tolerat full sun and wind.