This is a question that often confuses gardeners, and it is easy to see why. The simple answer is that begonias are both annual or perennial, depending on the cultivar grown.
Tuberous Begonias vs Rooted Begonias
This is where a lot of the confusion stems from. When treated with care, tuberous begonias can be overwintered and return the following spring more vigorous than ever. In contrast, the rooted cultivars tend to be only grown as annuals and will not survive their first frost.
You will most often find tuberous Begonias in fabulous hanging basket displays. Many of the spectacular trialling variety of Begonia are tuberous.
This type of Begonia can be overwintered and come back the following spring. However, you cannot simply leave them in the ground and expect them to show up next spring.
To overwinter the begonia tubers, you need to lift them out of the soil before the first frost. You will notice the leaves on these begonias starting to yellow near the end of their growing season. As soon as you see this happening, you can begin to set your plans for lifting them out of the soil for winter.
Once lifted, I like to leave the tubers in a sunny spot indoors for a couple of weeks to really help them dry out. Any retained moisture may result in rotten tubers. Once fully dry, store them over the entire winter in a cool, dark area. The only thing you need to be careful of is that they never get below 2-3 degrees Celcius.
Then come next spring, they will be ready to be carefully nursed back to life. We have a complete guide on how to start begonia tubers here.
The rooted form of Begonia is commonly grown as annual border flowers. Usually grown from seed, they are very often just grown to be an annual.
You can plant these outdoors as soon as the risk of frost has passed, and they will survive all summer long until the first autumnal frosts arrive. These are delicate plants and are very unlikely to survive a single frost. Hence most gardeners treat them as annuals.
Rooted Begonias can, however, survive the winter if they are brought indoors. This is not as simple as just bringing them inside at first sight of frost, however. If suddenly brought inside, the shock of the vastly changing conditions can have dire consequences for the plant’s health.
For this reason, you need to acclimatise them to indoor living. You can begin this process by initially only bringing them in overnight while leaving them outside during the day. Once you have been doing this for a few weeks, you are probably safe to bring them indoors full time. When keeping these flowers over winter, it is crucial to reduce watering. This will keep them in a semi-dormant state over winter. You can then begin watering more frequently come spring to help promote growth.
Because keeping rooted begonias over winter is not the simplest of tasks, many gardeners grow them as annuals and then plant fresh plants come the spring.