Controlled pollination
To maximise your chances of success, you will need to pollinate your begonia by hand. Take a male flower whose stamens* are slightly withered (a sign of maturity) and apply them (with a gentle, subtle back-and-forth movement) to the pistil* of freshly opened female flowers. If pollination has worked, a few days later the petals will drop and the pistils will turn brown. The fruit will gradually turn green and swell, then slowly dry out.
Harvest
The ripe fruit of a begonia is usually a dry, dehiscent* capsule* (loculicidal* capsule). However, some species (notably African epiphytes* and Asian shrub-like begonias) produce a fleshy fruit, or even a berry. Fruits are harvested on the plant when ripe. After harvesting, you will need to collect the seeds inside the fruits. For example, use a small tea strainer held over a sheet of white paper: the seeds fall onto the paper, while the fruit debris stays in the strainer.
Packaging and storage
The seeds should now be put in an airtight container (small plastic tube, small stamp bag…). They should then be stored somewhere cool and dark – a small fridge is perfect. Kept this way, they will last for several years.
Sowing
Sow in a seed tray, on a mix for young plants (light and low in nutrients – for example, light peat mixed with a little river sand). The seeds are placed gently on the surface of the pre-moistened substrate. Beforehand, mix a small quantity of seeds with a larger quantity of river sand, so you can better see how the seeds are spread over the tray.
Then place the tray in the dark, somewhere fairly warm (20 to 25°C) with high humidity*. Depending on the species, the seeds will germinate more or less quickly (from a few days to several weeks). If the seedlings are too dense, thin them out, i.e. remove the surplus seedlings to give the rest more space.
Pricking out
When the seedlings are well enough developed (cotyledons + 2 leaves), they need to be pricked out individually. This is the most delicate step, as some seedlings are barely a centimetre tall.
