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In the Magazine

Tuberous Begonias

In the Garden > Flowering Plants & Shrubs

Tuberous begonias (Begonia Tuberhybrida Hybrids) are among the most spectacular of all begonias but they are also the most difficult to grow. But, if you don't mind a challenge (these plants are definitely hobbyist plants), the results can be very rewarding.

Tuberous begonias are usually grown in pots, but there are also hanging basket varieties. These come from the original South American species but tend to be much easier to grow than other forms as they require less training (they are naturally pendulous) and are more tolerant of unsatisfactory conditions (including heat and humidity). These can be used as patio or fernery plants.

Plants can be grown either from seed or from tubers but in Australia are mainly grown from tubers. Planting a tuber of a named variety will guarantee that you will grow the same variety.

Origin

Begonias originated as rainforest plants in South America where they are now considered endangered in the wild. The name 'begonia' was given to this genus to honour Michel Begon (1638-1710), an amateur French botanist who collected begonias from Santo Domingo while stationed there with the French navy. Tuberous begonias were discovered later by an Englishman, Richard Pearce, in 1864.

Best climate

Tuberous begonias prefer a mild summer climate and are totally intolerant of high temperatures or very high humidity levels. The ideal conditions for tuberous begonias are areas where evening temperatures do not fall below 15C and where day temperatures are less than 27C (on average).

The best areas in Australia to grow tuberous begonias are Tasmania, south-eastern Australia (for example Ballarat in Victoria, where we filmed), the mild coastal areas of southern New South Wales, and cooler elevated areas such as the Blue Mountains.

Avid hobbyists have been known to attempt to grow tuberous begonias in areas such as Perth, Sydney and even Brisbane but these plants are a definite challenge in these warm climates.

Growing conditions

Begonias can be grown in a sheltered shadehouse, on a veranda, in a sun room, or on a window ledge. They are not glasshouse plants (although they are grown this way at Ballarat) as glasshouses become too hot in summer. In Ballarat summer cooling is needed in the begonia glasshouses.

Tuberous begonias grow best in partial shade or filtered sunlight. Exposure to excessive sunlight can result in burnt flowers and leaves. Too much shade results in foliage that is very lush with few flowers.

Growers recommend shade when the sun exceeds 50,000 lux. As full summer sun in Australia is 110,000 lux this means 50% shadecloth would be required in most areas. Normal interior light levels measure around 500 lux.

To assess the light levels at your place you need a camera with a light meter. With the camera set on 200 ASA and the shutter speed set at 1/125th second adjust the aperture (f-stop) as if you are taking a picture. You will get the following readings. With this system, a reading of F8 will give the best light levels to grow tuberous begonias.
  • F2.8 = 3200 lux
  • F4 = 6400 lux
  • F5.6 = 12,500 lux
  • F8 = 50,000 lux
  • F16 = 100,000 lux

Size and types

Tuberous begonias grow to about 30cm (12") tall but some varieties may reach 60cm (2'). Tuberous begonias are divided into 13 groups based on flower type or habit. They are usually described as singles, doubles, single frilled, daffodil-flowered, camellia-flowered, fimbriata etc based on the shape of the flower.

Flowers and colours

Flower heads consist of one large male flower in the centre and two smaller female flowers at the sides. Some flowers are very large (the size of a dinner plate). The smaller female flowers can detract from the male flower and, unless seed is to be collected, the female flowers can be removed to enhance the male. The males have double flowers and the females a single row of petals. One way of identifying begonias is by the unique sexual arrangement, and the other characteristic is the winged seed pod at the back of the female flower.

A huge range of colours are available including white, cream, yellow, pink, red, orange, scarlet and crimson. There are also bicoloured flowers. There are no blue-flowered tuberous begonias. Some flowers are fragrant.

Flowering is stimulated by daylength. Tuberous begonias will flower when the daylength exceeds 12 hours a day. This means plants will flower from mid December until late April. Most growers delay flowering for at least a month by removing buds. This encourages later but larger flowers. The optimum flowering period is from mid January to late March.
How to grow

By mid winter begonias are dormant. Between mid winter and early spring is the time to repot or plant tuberous begonias.

  • Planting: Tubers should be planted concave side up. Choose a pot appropriate to the size of the tuber. Generally this will be a 10cm (4") pot. The rule of thumb is that you should be able to fit two fingers between the pot and the tuber. Bury the tuber well down in the pot with a generous covering of soil (bury at twice the thickness of the tuber). It is essential to cover the tuber as roots develop from the top and sides. Always use an Australian Standard potting mix. Add some slow-release fertiliser such as Osmocote (3-4 month for flowering plants). Alternatively, water at each watering with a liquid feed applied at full strength.
  • Repotting: Hobbyist begonia growers repot their plants when they are around 15cm (6") high (usually in mid December). The small plants are moved up in to a 15cm (6") pot. A final repotting is done in late January, just before flowering. Depending on the vigour of the plant a 20cm or 25cm (8" or 10") pot is used. Reapply slow release fertiliser at this time.
  • Staking: Staking is required as the plant develops to support the flower head. Specially developed stakes, for example extendable wire props, are available from specialist begonia nurseries (listed below).
  • Cuttings: The tuber will get bigger from year to year. At four or five years of age the tuber will loose its vigour. It can be kept by taking cuttings, which will strike readily in spring forming a new tuber the following year.
  • Watering: Tuberous begonias do not like wet feet. Plants should be saturated and then rewatered when the mix is dry to the touch (probably once a week). Avoid wetting the leaves or flowers when watering.
  • Dormancy: By the end of autumn the plant is declining. Experienced growers recommend removing all growing tips in mid April and gradually withdrawing water as day and night temperatures drop below 15C. At this stage the plant is entering its dormant period. The leaves will yellow and drop. It is important to clean up the mess of fallen leaves and stems to reduce the chance of fungal disease. By late June or mid July the plant is fully dormant and the potting soil very dry. Remove the tuber from its pot, shake off soil and allow to dry out on paper. The tuber is stored in dry mix in a dark cupboard until it is replanted after about eight weeks (usually in early September). The tuber should be stored at around 15C and must not be exposed to frost.
  • Basket types: Naturally pendulous forms are best grown in hanging baskets. These are grown in the same way as the pot forms but as each tuber is slightly smaller three tubers are needed to fill a 20cm (8") basket. No staking is required.

Problems

Tubers will rot if they are too wet prior to planting. Keep them in an airy cool place over winter (do not expose to frost). Plants can also rot if over-watered. Powdery mildew (a white powder that forms on the leaves) can be caused by bad ventilation. Improve the air circulation or spray with Bayleton as a preventative measure.
Varieties

The following varieties are recommended by an experienced grower as being easy to grow and good for beginners:

  • Allan Langdon - red
  • Bernat Klein - white
  • Can Can - yellow with red edge
  • Ninette - pale pink
  • Sea Coral - apricot
The following varieties were filmed as part of Evan Hines' begonia collection in Ballarat:

  • Elaine Tartellin - rose pink
  • Scarbelle - small, bright, scarlet pendulous flowers
  • Roy Hartley - mid-soft pink
  • Sugar Candy - pink

Nonstops

An easier form of tuberous begonia are the so-called 'Nonstops', F1 hybrids which can be grown as bedding or patio plants. Nonstops are a cross between the multiflora type of tuberous begonia and some larger-flowered forms.

These plants are commercially available although not widely grown. Your nursery should be able to order plants for you (enquire at your nursery in June for spring planting as June is the optimum time to plant Nonstop seeds).

Nonstops are planted in the garden in late spring (November) in rich, well-drained soil which contains plenty of well rotted organic matter (such as compost). They will grow in warmer areas (for example Sydney) if given protection from hot afternoon sun. As with normal tuberous begonias the Nonstops are dormant in winter. At this time the tubers can be lifted, checked and replanted. If grown for a bedding display, the bed could be planted out with polyanthus in winter while the begonias are dormant.
Cost and availability

Tuberous begonias can be purchased in flower from your local nursery or florist for around $25 in flower. They can also be purchased from the following specialist nurseries (tubers are posted out each winter around August):
  • Begonia City Nursery, Wendoree, VIC, 3355. Phone: (03) 5339 2055. Named flowering plants around $20; Nonstop tubers start at $3.95.
  • Willsmores Begonia Farm, PO Box 280, Myponga, SA, 5202. Phone: (08) 8558 6217. Seedlings start around $4.50 each, the named tubers vary in price for each variety. Write or phone for a mail order catalogue. This nursery has named more than 24 Australian hybrids.

Further information

For more information on begonias contact the Begonia Society in your state.

NSW
The NSW Begonia Society
c/- Mrs Jean Whitten
15 Carlo Close
Kincumber 2251
Phone: (02) 4369 2967

QLD
The Queensland Begonia Society
c/- Peter Henderson
79 Chuter Street
Stafford 4053
Phone: (07) 3359 4319

SA
The South Australian Begonia Society
c/- Myrnie Jennings
4 Kinnaird Crescent
Highbury 5089
Phone: (08) 8264 6490

VIC
The Victorian Begonia Society
c/- Mr Phil Wright
74 Railway Place
Macedon 3440
Phone: (03) 5426 1298

WA
The Begonia Society of Western Australia
c/- Lyla Kilpatrick
Lot 17 Marri Park Drive
Casuarina 6167
Phone: (08) 9439 3173

Further reading

  • Growing Begonias by Peter G. Sharp (Kangaroo Press), rrp $19.95. ISBN 0-86417-933
  • Both tthe following books are out of print but may be found at your local library).
  • Growing Begonias by Eric Catterall (Timber Press, USA). Although an English book, it has good details and illustrations and is a useful reference.
  • Know Your Begonias by Jack Krempin (1994). This book is well illustrated and can be used as a guide for identifying varieties.

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