Once a king, always a king...

RHS Journals

The Garden
December 2006

Once a king, always a king...

Rex - or king - begonias with their bewitching leaf patterns can certainly lift spirits in winter months. In the wake of a recent RHS trial, Sally Charrett investigates a houseplant that holds court in a range of situations

Red numbers in the text refer to these cultivars of Begonia Rex Cultorum Group:

Mention rex begonias and you might recall a fusty, dark-leaved plant collecting dust in some corner of a drawing room, but this overlooked Victorian favourite still offers much for gardeners.

Grown primarily for striking, architectural foliage, rather than their insignificant pink or white flowers (often hidden by the leaves), more rex hybrids are available today than ever before, in a staggering assortment of leaf colours, shapes and textures. These are plants to suit every taste and domestic setting.

The heart, oval or star-shaped leaves come with smooth or wavy margins and range from teacup to dinner-plate sized. The indulgently textured leaf surfaces parade like the materials of a haberdashery - from velvet and satin-like to puckered, raised and glossy. These houseplants, often called painted-leaf begonias, have surface patterns in combinations of spots, streaks, splashes and swirls in pink, black, purple, red and metallic gold, silver and green - reminiscent of an artist’s palette. Plants also prove long lived.

In the USA, rex begonias are particularly popular, while in the UK, they are one of our top-10 favourite houseplants. Rex begonia leaves are also used by florists as cut foliage to edge bouquets. The plants can even be plunged outdoors for summer.

Indeed rexes were well prized by the late Christopher Lloyd who used them in his subtropical garden at Great Dixter in East Sussex. Begonia ‘Escargot’ 8 was a favourite of his, although temperamental; he found others such as B. ‘Burle Marx’ and B. ‘Little Brother Montgomery’ fared better. He is reported to have once said, ‘if I had to choose any group of plants to be stuck on a desert island with, I would choose foliage begonias’.

A royal introduction

Begonia rex is a species native to the remote, monsoon-soaked mountains of Assam, in the far northeastern corner of India, but most plants in cultivation referred to by this name are hybrids of that species and have been designated Begonia Rex Cultorum Group.

Though B. rex was brought to Britain in the ‘golden age’ of plant hunting in the mid-19th century, who first introduced it is unclear. Plant-hunter Charles Simons may have found it in Assam; some reports state the plant was introduced accidentally, growing with an orchid Simons collected.

Whether a collected plant or a welcome stowaway, B. rex soon after was fervently crossed with other rhizomatous Asian relatives to form hundreds of diverse cultivars that met with the fashion of the day for foliage plants. Primary parent crosses with Begonia rex include: Begonia annulata, B. decora, B. diadema, B. palmata, B. robusta and B. xanthina.

With the subsequent rise in popularity of flowering begonias, rex begonia fever cooled, but ‘the rex’ has never been entirely ousted from his throne. Many early cultivars have stood the test of time well, being passed down the generations by begonia specialists and enthusiasts. Begonia ‘Bettina Rothschild’, for example, is an 1866 French introduction (B. rex crossed with B. robusta) that is still enjoyed for the striking, long red hairs on its foliage, which prettily catch the sunlight. ‘Comtesse Louise Erdõdy’, a hybrid produced in 1883 by a gardener to the Erdõdy family of Hungary, was the first of the spiral-leaved crosses - a rex begonia characteristic that is becoming increasingly popular today.

Living with the king

The secret to successful cultivation lies in providing growing conditions within the home that match as closely as possible the natural environment of B. rex.

Its native habitat in Assam is characterised by high humidity and abundant cloud cover. Begonia rex plants therefore cope well in low light levels; indeed this enhances the leaves’ metallic lustre. In most cases such conditions can be achieved by positioning the plants by a north- or east-facing window during summer and a south-facing window in winter. Despite its aversion to direct sunlight, red and maroon colourings will deepen when grown in a bright location.

To keep humidity up, stand plants on a tray of moist pebbles, or group with other plants, for as well as having an aristocratic solo appearance, rex begonias associate well with other houseplants. Team with more simple, ideally narrow-leaved companions such as Aspidistra and indoor palms. Otherwise go for more dainty associations combining with plants such as maidenhair or asparagus ferns.

Aim for a daytime temperature of 21°C (70°F) to keep plants happy - avoid wide fluctuations; in winter do not allow temperatures to fall much below 15°C (60°F) as rex begonias will stop growing if temperatures fall too low.

Overwatering and lack of humidity are two of the most common reasons people lose these plants. Allow rex begonias to dry out slightly between waterings, and avoid standing them in trays of water to help to prevent rhizome rot. Use lukewarm water (cold will shock plants), and reduce watering when plants are dormant, especially in winter. Dry air results in crispy brown leaf margins and, in extreme cases, leaf drop. Underwatering and overwatering can both produce similar symptoms; yellowing leaves, wilting and leaf drop. Sickly-looking plants should be investigated to see if compost is overly wet or dry.

Begonia rex and its hybrids are shallow-rooted and so only need shallow pots. Clay pots are porous and will allow excess water to evaporate whereas plastic ones retain more moisture. Provided plants are not underwatered, clay pots are preferable in our cool, northern climate. Repot in spring only when the roots have filled the container.

Grow plants in slightly acidic (pH 5.8-6.8), light, free-draining compost. This can be achieved by adding grit, sand or perlite to a bark and loam-based or soil-less compost. Feed during spring and summer with a high-potash fertiliser (such as liquid tomato feed) following the manufacturers’ instructions.

Rex begonias are relatively slow growers. Newly-formed flower buds in late spring can be pinched out to promote more foliage growth, while the removal of stem tips will encourage branching and result in a more bushy plant. This is especially important to do when the plant is young.

Keeping on track

The arch enemies of rex begonias are mealybug and powdery mildew. Easily identified by a distinctive, crumbly white covering, mealybugs are a problem as they often lodge themselves in inaccessible parts of the plant. Spot-treat localised infections by removing with cotton swabs. For larger infestations, spray plants with a pesticide containing imidocloprid (Bayer Provado Ultimate Bug Killer).

Powdery mildew occurs when the compost is allowed to dry out, coupled with excessive humidity around the leaves. It manifests itself as white powdery patches on leaves, stems and flower buds. Minimise this risk by increasing air circulation around the plant, and keeping an eye on the moisture levels of the compost. Once a plant is infected, apply a myclobutanil-based product such as Bayer’s Fungus Fighter, taking care to follow the manufacturers’ instructions.

RHS trial of Begonia Rex Cultorum Group hybrids

During 2005, 87 Begonia Rex Cultorum Group hybrids were trialled in the glasshouse at RHS Garden Wisley; the plants were entered by several nurseries in the UK and one in the USA.

The Floral Trials Sub-Committee assessed the begonias in summer 2005; of the cultivars on trial, 25 received an Award of Garden Merit (AGM).

Nick Morgan, Superintendent of the Glass Department at Wisley and begonia enthusiast, said, ‘This has been one of the most successful trials and popular with visitors, but it is the tip of the iceberg with regard to numbers of different Begonia rex hybrids available’.

Among the AGM winners were:
‘Carolina Moon’ 14, which has large, showy, single-spiralled leaves and crisp markings of Nile green and purplish-red. An excellent specimen plant for a contemporary feel.
‘Martin Johnson’, popular with gardeners for its distinctive, jagged, grey-green, mauvish-purple foliage.
‘Midnight Magic’ 7, an easy-to-grow, single-spiralled plant with a dark green upper surface, rich red beneath, glows when in sunlight.
‘Roi de Roses’ 3 has a rose-pink hue and offers an interesting change of texture at the margins with purplish-red spots on a green background.
‘Sal’s Comet’ displays an attractive jagged leaf with bold markings. Metallic pink-purple with purple-brown edging.
‘Dewdrop’ 11 is a good miniature and fares well on windowsills. It is a ghostly, pale grey-green, mauve-pink at the centre and edges.
‘Mikado’ was one of the largest-leaved and most vigorous in the trial. It has contrasting pale-green colouring and darkish brown-red centre and fringe, red underneath with bright pink hairs.

Bulletin

Begonia Rex Cultorum Group Bulletin, now in production, contains details of B. rex cultivars that have received an Award of Garden Merit. For a printed copy, send an A4 sae (Large Letter 44p stamp) and £2 (a donation towards costs; please make cheque payable to Royal Horticultural Society) to: The Trials Office, RHS Garden Wisley, Woking, Surrey GU23 6QB.

View and download free PDF versions of all RHS trials bulletins

Taking leaf cuttings

First select a healthy leaf and, using a knife, remove the edges where leaf veins are less pronounced. Cut the leaf into 3cm-wide (2in) strips. Divide each into postage-stamp-sized pieces, each containing a section of main vein. Fill a seed tray with damp compost and lay the pieces on the surface; secure with wire. Cuttings will root in three weeks; plantlets should form by the sixth to eighth week. Remove these from the remains of the leaf and grow on in 9cm (3.5in) pots.

It seems that with more exciting cultivars becoming more widely available, this old favourite may regain its high profile with a new generation. So whether you are after a conversation-starter, something to go with your conservatory sofa cushions, or simply a shade-tolerant houseplant to brighten your living space, rex begonias have something to offer all domestic settings.

Suppliers

Suppliers of rex begonias include:
Dibley’s Nurseries, Denbighshire; 01978 790677; http://www.dibleys.com/
Rhodes & Rockliffe, Essex; 01992 463693
Shirley’s Plants, Merseyside; 01704 213048; http://www.stbegonias.com/

Sally Charrett is the Trainee Horticultural Journalist with The Garden

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