Seed of fibrous rooted begonia should be sown in pots or trays of seed compost in February or March and maintained at 21-25°C (73–80°F). The seeds are very small and should be sown on the surface of the compost and covered with no more than a light dusting of silver sand, or cover pots with cling film. When the seedlings have produced their first true leaf, prick out into boxes of fresh compost and grow on, potting first into 7.5cm (3in) pots, then into 13cm (5in) pots.
Leaf cuttings of certain types such as Begonia masoniana and B. rex hybrids may be taken in May or June. Choose newly matured leaves. Cut off the leaf stalk, then, using a sharp blade, carefully cut through the major veins, spacing cuts about 2.5cm (1in) apart. Then place the leaf with its top surface uppermost on a seed tray of sandy cuttings compost. Peg or weigh down at intervals to ensure the cuts are in contact with the compost, water in well then place in good light but preferably not direct sun. Place in a propagator at a temperature of 18–24°C (64–75°F) with a high relative humidity. Individual plantlets forming at the points of vein cutting should be potted up into 7cm (3in) pots and grown on, once they have two or three leaves.
Stem cuttings may be used to propagate fibrous rooted and cane-stemmed begonias. Take 7–10cm (3–4in) cuttings in April, insert in a sandy cuttings compost and root with bottom heat of 18–21°C (64–70°F). For rhizomatous begonias cuttings may need to be longer than 10cm (4in) so as to include a leaf node at the base.
Semi-tuberous begonias are usually replaced each year from cuttings. After flowering, plants should be allowed to rest by reducing the temperature to 7°C (45°F) and reducing the water but not allowing them to dry out, for about six weeks. At the end of this period, plants should be pruned back to within 15cm (6in) of the base, and the temperature raised to 10–13°C (50–55°F). When the new growth is 5–7.5cm (2–3in) long, take basal cuttings of these shoots and root at 18–22°C (65–71°F). Keep lightly shaded until well rooted then pot up. Pot on as necessary until the plants are in 12.5–15cm (5–6in) pots.
Divide rhizomatous begonias in spring, ensuring that each portion of the rhizome bears one or more growing points.