More exploration into tropical regions reveals new wild begonia species each year; currently more than 1,500 different begonia species are known. Begonia seeds, which are like tiny grains of fine sand, are spread by breezes or rainwater runoff. Horticulturists most often employ vegetative propagation techniques to make new begonia plants; leaf, stem or root cuttings guarantee an exact genetic clone. Pollination of begonia flowers yields seeds and new plants with a random blend of new genes to potentially create more interesting plants or hybrids to grow in the garden.
Look for the ripening female flowers on the begonia plant. Female blossoms lack any yellow stamens that shed powdery pollen, and if you look at the back side of a female flower, you'll seed the swollen ovary at the base of the petals. Once the flowers are finished blooming, the petals dry and are shed, eventually leaving only a maturing ovary.
Allow the maturing ovary to remain on the begonia plant to ripen the seeds that are inside. According to Brad Thompson, in an article for the American Begonia Society, the ovary on the majority of begonia plants takes more than a month to mature. During this time, keep your begonia healthy so it will naturally develop seeds.
Remove the seed pods once the flower stems begin to dry and shrivel. Thompson says to clip the pods off with a small scissors whether they look fleshy or dry. If you're uncertain if they're ripe, keep them on the shriveled flower stems until they look quite dry, but you want to remove them before they dry completely and split open to release the seeds. Put the pods on a piece of typing paper so you can easily handle them and slide them into storage containers.
Place the harvested pods in a small medicine bottle, old film roll case or other plastic or glass container. Curl the typing paper like a funnel so you can slide the pods easily into the bottle. Do not put the cap on the bottle; you want air to fully dry the pods. Place a piece of masking tape or adhesive mailing label on the bottle and write any identifying data on it, such as the name of plant the pods were harvested form, the genetic parent plants and the date harvested.
Dry the begonia seed pods for a week in the bottle.
Break open the seed pods atop a piece of clean, blank typing paper in a windless environment. Both tiny seeds and pod chaff will fall onto the paper. Work slowly and try not to breathe atop the area to avoid inadvertently blowing seeds off.
Gently tilt the paper with seed and chaff over another clean sheet. The tiny seeds will roll onto the paper, leaving the chaff behind.
Curl the edges of seed-carrying paper into a chute or funnel and slide the seeds into a waxed stamp envelope. Or cut the typing paper into small squares and fold them carefully shut into tiny envelopes.
Seal the small envelopes with a piece of invisible tape. You do not want any openings where the tiny begonia seeds may roll out.
Transfer any information from the seed pod storage bottle onto the envelopes. This is particularly important if you need to recall the hybrid cross origins for the seeds. Put the date of seed harvest to let you know it is recent when you later sow the seeds.