Making the best of pot plants and bedding stalwarts
Begonias are an ideal pot plant or for use in bedding schemes – here’s how to grow begonias for the best show in your garden. The first thing to find out is whether they are tuberous or fibrous-rooted. Tuberous varieties grow from a large swollen root or stem, or tuber, and have large, showy flowers. Fibrous-rooted begonias have smaller but more numerous flowers.
How to grow begonias – tuberous-rooted
Look for cultivars derived from Begonia × tuberhybrida for bright colours and a long flowering season. Male and female flowers appear on the same plant, with the males being the biggest. Hybrids of B. boliviensis are excellent plants for baskets and pots.
- Place tubers on the surface of peat-free compost in a seed tray, hollow side uppermost, 2cm apart and 2.5cm deep in March or April.
- When leaves appear, pot on into 10-12.5cm pots of peat-free multipurpose compost.
- Harden plants off gradually during May and place outside after the last frost.
- Feed every week with tomato fertiliser from July until September.
- Grow in sun or partial shade.
- Support the brittle stems with canes.
- Water regularly but avoid wetting the foliage.
- Lift tuberous begonias before the first frosts. The leaves will yellow – reduce watering at this time. Store dry tubers in barely moist soil or sand in a frost-free place, at around 7°C. Water occasionally to prevent shrivelling.
- If growing tuberous begonias for exhibition, you can remove the female flowers for bigger blooms. However, this isn’t necessary for gardens.
How to propagate tuberous begonias
- By division: When shoots appear on the tuber, cut it into sections, ensuring each one has at least one bud. Let the cut end callous (dry out) for several hours. Pot on individually, placing the tuber level with the compost’s surface.
- By stem cuttings: Take a 10cm cutting with a section of tuber still attached (a heel) in spring. Insert into sandy rooting compost in a propagator set at 18-21°C, or place on a sunny windowsill.
Fibrous-rooted or Semperflorens begonia
Although also tender perennials, fibrous-rooted begonias are usually grown as annuals and discarded at the end of the season (you can overwinter them as houseplants). They produce mainly white, pink or red flowers freely until the first frosts and often have attractive foliage.
- They are particularly valuable, as they are one of the few bedding plants that grow in partial shade.
- Either grow from seed or buy young plants. Harden off and plant out after the last frosts.
- Feed containers weekly with tomato feed.
- Water regularly, but don’t wet the foliage.
How to propagate fibrous-rooted begonias
Growing from seed: Sow in trays of seed compost in February/March in a propagator at 21–25°C. The tiny seeds should be sown on the surface as light is needed for germination. Cover with cling film. Prick out into trays, then pot on in 7.5cm pots, then 13cm containers.
By stem cuttings: Overwintered plants in a conservatory or sunny windowsill can provide new stock. Take 7.5cm–10cm cuttings in April. Insert into sandy rooting compost in a propagator set at 18-21°C, or place on a sunny windowsill.
How to grow begonias – common problems
- Tubers can rot in wet conditions. Make sure compost is well-drained and stand pots on pot feet to prevent waterlogging.
- Flowers drop in dry conditions.
- Tubers can rot in storage, so check regularly
- Tuberous begonias may suffer from powdery mildew, fungal leaf spots, or Phytophthora root rot.
- Foliage may scorch in full sun.
