Tuberous begonias will come back year after year, and with every passing season, the tubers will grow in size. Once they are getting quite large, you may start to think about dividing them down and creating new plants. Just be aware though, that new, smaller tubers will not provide as many flowers as older larger tubers will.
How to split the tubers
Splitting begonia tubers is relatively straight forward, although I must warn you that freshly cut tubers are more vulnerable to rot and infection, so the process is not without risk.
Step 1 – Find a suitable tuber.
A tuber ready to divide should be large and also have at least two clear stems. Please note the tuber I split here in the images is nowhere large enough to need splitting but it is all I had on hand to demonstrate with!
Step 2 – Cut with a sharp knife.
Cut the tuber with a sharp knife directly between the two stems.
Step 3 – Leave to dry.
Now I like to place the tuber on a piece of kitchen towel and leave it in direct sunlight for a couple of days. I find this helps to start the scabbing process on the cut and thus reduces the chance of disease and infection.
Step 4 – Replant.
Now I replant the tuber on the surface of some good, high-quality compost.