Begonias are a much loved summer bedding plant suitable for pots, tubs & hanging baskets.
It’s a family of two strains: fibrous rooted & tuberous begonias.
Fibrous rooted Begonias are usually sold in a bedding pack of 6 or so plants. Like all begonias they are tender plants in the UK and can be planted out after the last spring frosts. They are grown from seed and as the name suggests their roots are fibrous. They live all summer long and will be killed in the autumn be the frosts. They flower continuously from May/June until October/November and are great value.
Tuberous Begonias grow from a tuber. This is an enlarged storage organ that grows below ground. It builds up during the summer months to allow the plant to grow again the following year by using the stored energy to grow new stems & shoots from buds on their surface. A Potato is also a tuber. When you buy a tuberous Begonia you buy the dormant tubers in the winter season. They are then ready to be grown for the summer flowering season. Begonias are not winter hardy so at the end of the summer the tubers are stored in a frost free place to be grown again the following year.
Growing tuberous Begonias
From January until late April tuberous begonias are available to buy. They are usually in packs and include a picture of the flowers plus information about the begonia. You may often see the first signs of the new shoots growing from the buds.
When you get them home you should keep them dry and frost free until you are ready to start your tubers into growth.
Begonias shouldn’t be planted in your garden until the last frosts have passed which is usually in late May or even early June in the north. From starting into growth to planting they must be grown in warmer conditions. This could be a heated greenhouse or conservatory in February or March, both unheated in April or on a windowsill in your home.
Start them off sealed in a poly bag of damp multipurpose compost. Place them somewhere warm. An airing cupboard s perfect. Check them daily and as soon as the buds break, as in the picture here, remove them from the warm and dark. Fill 5″ (13cm) pots with multipurpose compost as you place the poly bag in the warm and dark. This allows the compost to warm in the final growing spot.
Remove the tubers from the poly bag and place the tuber on the surface of the compost in the pots. The buds always grow from the hollow side of the tuber. The rounded side has some wispy roots from the previous year showing. This is the side that must be in contact with the compost. Push the tuber gently into the compost leaving the hollow side above the compost.
Cover the pots with clear polythene bags held with an elastic band for a few days to help the roots to grow. Once growth has started, remove the bag & water occasionally as needed. Feed only once a month with a general liquid feed until you plant them in their final spot or container.
If you have the room, such as a greenhouse, you can grow the tubers straight in a hanging pot, hanging basket or patio pots that they will grow in during the summer. Alternatively re-pot the growing plants into their final container in late April or May. As it is usually warmer during the day in late spring you can place your finished containers outside in a warm, sheltered spot during the day, bringing them inside at night to avoid the cold. Although frost is a killer, cold nights below 7 C won’t help these semi-tropical plants thrive, so don’t rush the process. You won’t regret it. Mix into the compost in the final planting Gro-Sure Slow Release granules. These clever granules feed for up to six months and are a high potash feed. This will produce the most flowers.
Occasionally remove any fading flowers to keep the plants productive and attractive.
Autumn and winter
Eventually summer fades, the days get shorter and temperatures drop. Your begonia plants will battle on as the autumn progresses and often still look magnificent into November. To store the tuber for the following year you can either place the pots or baskets in a greenhouse or conservatory, stop watering them and let the compost dry out.
Alternatively leave the pots outside and let the first hard frost kill the tops. It’s not attractive but it does the job. It’s essential then that you ‘dig’ the tubers out of the compost, bring them inside your house and let them dry off on a windowsill or kitchen tray. Once the remaining compost dries and falls off with the old roots, the now dry tubers can be stored in paper bags in a frost free place until February or March for you to start again. Paper bags are essential. The tubers need to breath. In a polythene bag they won’t. Write the colour or variety, if you’ve noted it, onto the bag so you can have successful colour schemes in future summers.