There are some 2000 species of Begonia and they are native to moist, subtropical and tropical climates. They produce lovely bushy plants in a wide range of colours but as their stalks are fleshy, they do not lend themselves to be used as cut flowers. Hence in the show they are always exhibited as a pot plant.
As with Dahlias they require very little maintenance and are relatively pest free. Similar to Dahlias, they reach their prime in late summer and autumn. Hence, they are an ideal choice for our show which is held in August.
I should mention here that as well as tuberous begonias you can also buy bedding begonias which have fibrous roots. Bedding begonias are annuals and unless you are prepared to keep your greenhouse at summer temperatures all winter, you can forget about overwintering them. I will only discuss tuberous begonias in this article.
The picture below shows both types. The Bedding begonias are in the foreground.
In their native climates, Begonias are perennials, but in the UK they are not hardy. The first frost will reduce your beautiful blooms to a mushy mess, but below ground the tubers will be entering a state of dormancy, so the essence of keeping your plants is to preserve those tubers from the worst winter can throw at them.
As with Dahlias you can overwinter Begonias in their containers. The method is the same as for Dahlias.
As soon as the begonia plant has lost its form, remove all the foliage to just above soil level.
Then store in a frost-free place. Remove any dead foliage as soon as it appears.
Preserving Tuberous begonias from garden beds
Begonia Tubers are less hardy than Dahlia tubers and the likelihood of them surviving outdoors over winter is very small. They will also rot if they get too wet. Therefore, they need to be removed from the beds.
You can dig up the tuberous begonias as soon as they have lost their summer shine, but certainly within a few days of a severe frost. Leave a small amount of soil around each tuber and cut off any remaining foliage to about 1 inch above the tubers.
Check for damage or Vine Weevil larvae before proceeding to the next step.
Space the tubers on a tray and leave in a cool, dry area until the surrounding soil is dry, then carefully remove any of the remaining soil.
Place a layer of peat moss, vermiculite, or moist potting compost in a small cardboard or wooden box. Lay out the tubers on the first layer. If available, dust your Begonia tubers with sulphur powder to guard against rot. Then add another layer of your chosen storage medium. You can add repeat layers if necessary. Ensure that the tubers do not dry out completely.
As an alternative, once dry, tubers can be stored individually in paper bags. (do not use polythene bags for this as the tubers may sweat and eventually rot.)
Store the tubers in an area where they can be kept above freezing point. This could be a garage, shed or conservatory. Check them periodically over the winter and remove any diseased or decaying tubers.
As soon as the threat of frost is over (or in a heated greenhouse), plant the individual tubers in pots (hollow side up and just below soil level) with fresh fine compost and water lightly.