It can definitely be a bit tricky to get your Begonia to survive the winter in climates where it can't grow outside. There are, however, some tips and steps you can follow to give your plant the best possible conditions:
Overwintering Tuberous Begonias
In fall: dig up your tuberous Begonias and store them indoors during winter. You can dig them up once the foliage has faded or directly after the first frost. Remove as much soil as possible from the tubers, place them on a dry surface such as a newspaper and then leave them in a sunny spot for a week or so until they're fully dry. Clean away any more excess soil and any remaining leaves. You can then store the tubers in a paper bag or on newspaper in a cardboard box in a cool, dark and dry location until the spring arrives again.
Overwintering Annual Wax Begonias
Wax begonias and other non-tuberous Begonias can be brought inside instead of being dug up before the colder months arrive. For these Begonias we recommend the following:
Check the soil Before moving your plant from where it has been during spring / summer, make sure the soil is dry to avoid mold growth.
Check for pests When your plant is moved to a new location and proceeds into the winter months, it might get a bit weak. Its normal resilience against pests is therefore lower. Make sure to check that your plant is healthy and free of pests before moving it to its winter location.
Lower the temperature Place your plant in a cool room. For example, a garage, shed, basement, attic, summerhouse or a cool stairway if you are living in an apartment. Recommended temperature for this plant:
Add extra grow light Pick a full-spectrum light bulb and place it 20-30 cm / 8-12 inches above the plant to prevent leaf burn. Keep the light on for 8-14 hours / day.
Reduce watering Cutting back on watering during winter is key to helping your Begonia to survive. The amount of water it will need will depend on the amount of light it will get and what temperature it's placed in. But in general: it's better to water it a bit too little during winter than a bit too much.
Keep an eye on it Keep checking your Begonia from time to time to be able to stop any infestations at an early stage. It's also important to keep an eye out for drooping leaves since that often is a sign that there's something going on with watering / the amount of light. So, check the soil and the roots and make sure that everything is okay regarding the amount of light and temperature conditions.
“Is it starting to get leggy or droopy? Make sure that everything is ok regarding lighting and drainage and adjust the amount of water if needed." — PLANTA TIPS