How to Overwinter Begonias
Article by David Marks
There are two main types of begonias commonly grown in the UK. Those which are annual and grown from seeds / plug plants and those grown from corms, small bulbs. It is the corm type which can easily be overwintered if you follow our step by step instructions.
To successfully overwinter the corms you need to plan ahead slightly to ensure they are in the correct condition for winter storage. This article is organised in the form of a step by step diary to make the process easy to understand.
Dates given are average for the UK; if you live in a cool part of the country start the process about two weeks earlier. For those in warmer part of the UK start the process off about two weeks later.
EARLY TO MID SEPTEMBER
Flowering will naturally cease because of colder temperatures and shorter day length. Slightly reduce the amount of watering but do not stop altogether. The corm is still in the process of fattening up for overwintering.
Cease feeding with a nitrogen rich fertiliser instead feed lightly with a tomato plant fertiliser. This will tend to harden up the corm as well as provide it with the correct nutrients.
Cooler weather will have turned the foliage yellow and when the majority of green growth has ceased, stop watering altogether and move the container / basket out of the way of rainfall. Now id the time to let the compost start to dry out.
As leaves yellow and start to fall off remove any plant debris to prevent any mould forming. The top of the corm is the area most at risk.
MID TO END OCTOBER
By the end of October the main stem will have withered and can be removed when it comes away easily from the corm. Leave the corm for three to five more days to allow the top of the corm to heal over.
Lift the corm out of the compost and shake / tease away any compost attached to the roots and the corm. Inspect and only keep ones which are free from rot.
The corms can now be stored for winter. The ideal place is a cool but frost free area which is dry and dark. Our preferred method is to store them in individual paper bags in a cardboard box. Somewhere like a garage or an unheated room in the house is ideal. A greenhouse is not the best situation because it can become damp.
If you can remember, check them every couple of weeks to ensure they are not rotting, dispose of any that are. They can remain where they are until ready for revival the next year, normally around mid-February.