Rex begonias are mostly grown for their colourful foliage. The leaves range in colour from silver to purple and red. The colours are often mottled or striped and can add intrigue to a shade garden. Rex begonias also make excellent houseplants. Begonias are easily started from cuttings, but seeding works almost as well. Seeds have variable germination time and can breed less true than a cutting. However, the process is simple and can lead to some interesting variations.
Types of Rex Begonia Seed
There are two kinds of seed available to grow Rex begonias. Hybrid seed is created by cross-pollination of one variety with another variety of begonia. Species seed results when you self-pollinate a wild species. This is the only way to get true seed. Species seed can be pollinated with the pollen from its own flowers. Genetic diversity can only be maintained if you pollinate with pollen from the same species but a different plant. Hybrid seeds can be pollinated in any manner. The plant can be self-, cross- or open-pollinated, and any seed that results is a hybrid seed. You really never know what you will get if you use this method.
Harvesting Rex Begonia Seed
Once pollination has been achieved, it can take up to a month for the pods that form to ripen. The flower stems will dry up, and the pods can be taken off. The pods need to dry for a week in an open container. They will split and open when the seed is mature. The seeds need to be separated from the pod and the chaff. Good seed looks like popcorn kernels under a magnifying glass. The seed looks like red dust to the naked eye. Rex begonia seed can be stored in a closed container or paper envelope in the refrigerator for years, or you can plant the seeds immediately in the fall.
Planting Rex Begonia Seed
Rex begonias need heat, humidity and low light to grow. The seed can be sowed in a tray with damp sphagnum moss. The seed doesn't need to be covered, but the tray should go on a seed mat or heat source. Rex begonias germinate in 10 days on average, but the process can take up to two weeks. Rex begonias need humidity, so the trays can be misted daily. Once the seedlings leaf out, the first leaves will simply be green. It will take a year to get variations in the leaf colour, and each year the leaves will be different.