My potted Rex begonias are overgrown

(Question)

I have 3 varieties of Rex begonias in pots, which they’re now growing out of.  The stalks are almost bare of leaves, except at the ends.  And there are stems, or branches, growing out of the soil. My poor begonias are basically not very handsome any more. What can I do?

(Answer)

Thank you for inquiring about these wonderful hybrids.

Begonia is a genus of tender perennial flowering plants, in the family Begoniaceae. Rex begonia hybrids, in the case of your plants, have been developed to feature beautiful, unique leaf shapes, markings and colors. The leaves grow on short leaf stalks, from the plant’s underground rhizomes. The leaf edges, and undersides, are covered with short red hairs. While the beauty of these hybrids is all about the leaves, they do flower, but the generally pink flowers tend to be small and incidental. In fact, the flower stalks are often removed, to prompt the plant to focus energy towards leaf growth.

The “stems” you mention are actually rhizomes. Your plants have become older, and have developed rhizomes that have moved above the soil. Any plant usually gets happier when it’s trimmed (keep your healthiest cuttings for propagation, below) and given new, well-draining potting mix, and a larger pot to stretch out.

You can easily propagate a new begonia plant either from stem sections, or leaf cuttings. Since you seem to have more stems than healthy leaves, your best method of propagating might be to plant 10 cm (4 in) begonia cuttings directly into a growing medium. Use the stems you trimmed off the “mother” plant for your cuttings, with some leaf growth at the end. Cut just below several nodes.

Make an angled hole in your planting medium with a pencil, or a chopstick, and insert your stem into the hole, burying several of the stem’s nodes. Tamp down the medium to support the cutting. Many gardeners cover the pot with a plastic bag, or a plastic bottle with the bottom cut off, to make a mini-greenhouse. Choose whichever method will allow you to best regulate air flow, and moisture. The beauty of growing your Rex begonias in pots, indoors or out, is that you can easily control their light, air humidity and soil moisture needs. Remember, they are a tropical plant that needs bright, but indirect light. And while they require moisture, they will not tolerate wet feet. Think  “orchids ” and you have a good rule of thumb to follow.

So there you have your “mother” plants  freshly set up in new pots, and their progeny well on their way.

For further reading, attaching links to the American Begonia Society,  http://www.begonias.org/greenhouse/rhizomatous.htm

… and the Royal Botanical Society:   https://www.rhs.org.uk/Advice/Profile?PID=814