Begonias: houseplants

Begonias such as Begonia Rex and Begonia metallica are popular houseplants grown for their attractive foliage or flowers. The leaves may have bold shapes or striking, often silver markings. The advice given here will help guide you to growing success.

Begonia rex

Quick facts

Common name Begonia
Botanical name Begonia
Group Tender perennial
Flowering time All year
Planting time Any season
Height and spread 10-60cm (4in-2ft) by 10-45cm (4-18in)
Aspect Bright filtered light
Hardiness Frost tender
Difficulty Moderate

Cultivation notes

Begonias for growing indoors are divided into four main groups.

  1. Fibrous rooted begonias are tender perennial evergreens with erect sometimes shrubby stems. This group includes Begonia schargii and B. metallica. Some are grown for their flowers but most are valued for their foliage, which may be of bold shapes or strikingly marked, often in silver.
  2. Cane-stemmed begonias are woody, fibrous-rooted, evergreen tender perennials. Their stems are erect, smooth and bamboo-like, with swollen nodes. They are grown for their large and long-lasting pendulous flowers, and their marked foliage. Most forms grown today originate from species native to Brazil, such as B. stipulacea and B. maculata.
  3. Rhizomatous begonias: Begonias in this group, such as B. masoniana and the hybrids of B. rex are tender, evergreen perennials growing from a creeping rootstock. The majority of them are grown for their foliage which is often brightly coloured.
  4. Semi-tuberous begonias are represented by cultivars of B. × hiemalis (syn. B. × elatior), a hybrid between B. socotrana and B. × tuberhybrida).  These are largely winter-flowering plants whose hybrids are grown as florist's pot plants. This group of hybrids are not intended for long-term cultivation and are often discarded after flowering. Modern cultivation methods used in nurseries have resulted in year-round availability of these plants.

Care

Fibrous rooted begonia

  • Protect from direct sun to avoid scorching leaves
  • Maintain good levels of humidity by standing the container on tray of gravel, expanded clay granules (Hydroleca) or recycled lightweight aggregate (Hortag) and keep moist, with the water level slightly below the surface of the gravel
  • Do not mist or neglect ventilation as begonia mildew can be a problem in damp over-humid conditions
  • In glasshouses ventilate once temperatures reach 18°C (64°F)
  • Feed established plants every two weeks from May to September with a high potassium plant food
  • Do not allow compost to dry out but avoid overwatering
  • Grow in a multipurpose compost, ideally peat-free and based on coir to avoid sciarid fly problems, or John Innes No 2
  • Provide a winter minimum temperature of 13°C (55°F)

    Cane-stemmed begonias

    • Require good light to produce sturdy stems and abundant flowers; however they need protection from direct sun to avoid scorching leaves
    • Best grown in a temperature range of 15-22°C (58-72°F)
    • Do not allow compost to dry out but avoid overwatering
    • Reduce watering in winter
    • Maintain good levels of humidity by standing the container on tray of gravel, expanded clay granules (Hydroleca) or recycled lightweight aggregate (Hortag) and keep moist, with the water level slightly below the surface of the gravel
    • Feed established plants every two weeks from May to September with a high potassium plant food
    • Grow in a multipurpose compost, ideally peat-free and based on coir to avoid sciarid fly problems, or John Innes No 2

    Rex and other rhizomatous begonia

    • During summer keep plants shaded and watered freely but with good drainage and high relative humidity (humid atmosphere)
    • Do not wet the leaves or the crown
    • During winter reduce watering, allowing the surface of the compost to dry out before watering again
    • Minimum winter temperature of 10°C (50°F) is required for all of these types except B. bowerae, B. masoniana and B. rex which require a minimum temperature of 13°C (55°F)
    • Feed every two weeks from May to September with a high nitrogen fertiliser

    Semi-tuberous begonias

    • Position in semi-shade
    • Keep adequately moist but do not let the plants dry out
    • Require high levels of humidity
    • Maintain a temperature of 10-13°C (50-55°F) during flowering

    Propagation

    Seed of fibrous rooted begonia should be sown in pots or trays of seed compost in February or March and maintained at 21-25°C (73–80°F). The seeds are very small and should be sown on the surface of the compost and covered with no more than a light dusting of silver sand, or cover pots with cling film. When the seedlings have produced their first true leaf, prick out into boxes of fresh compost and grow on, potting first into 7.5cm (3in) pots, then into 13cm (5in) pots.

    Leaf cuttings of certain types such as Begonia masoniana and B. rex hybrids may be taken in May or June. Choose newly matured leaves. Cut off the leaf stalk, then, using a sharp blade, carefully cut through the major veins, spacing cuts about 2.5cm (1in) apart. Then place the leaf with its top surface uppermost on a seed tray of sandy cuttings compost. Peg or weigh down at intervals to ensure the cuts are in contact with the compost, water in well then place in good light but preferably not direct sun. Place in a propagator at a temperature of 18–24°C (64–75°F) with a high relative humidity. Individual plantlets forming at the points of vein cutting should be potted up into 7cm (3in) pots and grown on, once they have two or three leaves.

    Stem cuttings may be used to propagate fibrous rooted and cane-stemmed begonias. Take 7–10cm (3–4in) cuttings in April, insert in a sandy cuttings compost and root with bottom heat of 18–21°C (64–70°F). For rhizomatous begonias cuttings may need to be longer than 10cm (4in) so as to include a leaf node at the base.

    Semi-tuberous begonias are usually replaced each year from cuttings. After flowering, plants should be allowed to rest by reducing the temperature to 7°C (45°F) and reducing the water but not allowing them to dry out, for about six weeks. At the end of this period, plants should be pruned back to within 15cm (6in) of the base, and the temperature raised to 10–13°C (50–55°F). When the new growth is 5–7.5cm (2–3in) long, take basal cuttings of these shoots and root at 18–22°C (65–71°F). Keep lightly shaded until well rooted then pot up. Pot on as necessary until the plants are in 12.5–15cm (5–6in) pots.

    Divide rhizomatous begonias in spring, ensuring that each portion of the rhizome bears one or more growing points.

    Cultivar Selection

    Begonia rex: Evergreen perennial to 30cm, with large, obliquely ovate leaves which are metallic green with a silvery zone on the upper surface, reddish beneath; panicles of small pink flowers in winter. There are many cultivars available with attractive coloured and patterned leaves.

    Begonia 'Lucerna': Strong-growing, erect cane-stem begonia with obliquely ovate, olive green leaves heavily spotted with silver, and large panicles of pink flowers 3-4cm across in summer.

    Begonia 'Tiger Paws': Rhizomatous begonia to 25cm, with rounded, lobed dark green leaves with darker markings, and small sprays of pink flowers.

    Problems

    Leaves: Brown edges to the leaves can be caused by low humidity or too high a temperature. Rotten leaves and leaf drop these can be a result of too much humidity, over-watering or low light levels. Yellow leaves may be due to low light levels or over or under-watering. Most casualties reported through RHS Gardening Advice have been over-watered or kept in too dry an atmosphere

    Flowers: Bud drop may be due to dry air or under-watering.

    Also watch out for pests such as aphids and red spider mite and powdery mildew.

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