Growing Tuberous Begonias For Exhibition


Some years ago, a lady visiting my greenhouses in August, and having been totally captivated, by the begonias which were in full bloom, posed the question” Why do you grow these beautiful plants in the seclusion of these shaded greenhouses and away from the view of the public?”

My first answer was that they gave me great pleasure each day, giving them my full attention and then just to relish the wonderfully peaceful atmosphere backed up by the wonderful song of a blackbird, which was nesting nearby. After a little deliberation, I then related an experience which had occurred in my formative years, at a Leeds Flower Show, and which has happened at every show, ever since. It is a wonderful reason for exhibiting Begonias - communicating happiness to others.

I had been standing next to one of my prize winning exhibits, feeling quite pleased with myself, when some ladies stopped to admire the plant, with the exclamation, “What are they? Are they real?” Although they fingered the blooms and tried to sniff for any perfume, their admiration was sufficient reward for all of the work, which I had put into the growing, and the transporting of the exhibits.

It is therefore one reason for growing and exhibiting This is that we can share the beauty of our plants or blooms with others. It seems to me that a goodly number of people are starved of colour and this is brought home by the frenetic crush to buy plants or blooms at the end of each show.


It is absolutely necessary to have a suitable structure in which to grow them.
Begonias only require 45 degrees F i.e. cool, airy, shaded conditions, with protection from the elements. If the greenhouse is too small, a day with intermittent cloud would cause yo-yoing variations in temperature and this would cause bud drop.

Should you be in possession of say an 8' x 8' greenhouse, good quality automatic ventilation is a must. In order to prevent the access of insects, these vents should be protected by fine netting and, as the warmer weather appears, the door will require to be fitted with netting too. Amore suitable size of greenhouse would be a 15' long one. Bottom ventilation will greatly assist in the circulation of the air. if set to cut in at 60 degrees F, a thermostatically controlled fan will greatly benefit the plants. Care should be taken that neither the vents, nor the fan, direct the breeze in a manner, which will disturb the blooms. Untold damage can be imparted to the tender petals if they are ruffed against the serrated edges of the leaves.

The glass will require shading by the end of March. This can be done by applying a watered down emulsion paint to the outside of the greenhouse or by pinning Agrifleece, a spun bonded polyester fabric, to the inside of the glazing bars. Both types of shading will be required in mid-Summer. Coolglass is readily available in the shops and it is easily applied.

Benches should be as low as possible as they will keep the plants away from the hottest part of the greenhouse, which is at its apex. An ideal height is 12"to 15" and the benches should be slatted to permit air circulation, from bottom ventilation.

Before housing ones tubers or plants each year, hygiene must be practiced. A sulphur candle will kill the insects and moss. The greenhouse should be closed down whilst this is carried out, and then left another day, before bringing the plant material back in. Although a thorough scrubbing down and spraying with Jeyes fluid is an alternative, it does not permeate the nooks and crannies the way the smoke does.Jeyes fluid solution is ideal in which to immerse ones pots.

Choice of heaters is of paramount importance. Paraffin generates too much moisture and is too expensive as it is difficult to control thermostatically. It also smells terrible!

Solid fuel heating is labour intensive and the boiler may go out when the wind is blowing in the wrong direction. Electric, although the cleanest, is the most expensive, if one has a cheap tariff supply
(Operating from 12 midnight to 7a.m.) A changeover relay can be fitted to allow the ordinary tariff supply to cut in during the day, or the Supply Authority who has a radio signal operated meter system, which does all of this.

If North Sea Gas is available, sophisticated heaters, accurately controlled are now readily obtainable.Bottled Propane Gas heaters are the next best, but a changeover device will be required in order that, should, one bottle empty, the device will automatically cut in the standby bottle and indicate this by means of a red flag in the window of the device, leaving ample time to order a new bottle.

Whatever kind of heat employed, please remember that every five degrees above 40 degrees F - the bill DOUBLES! Remember also, that begonias only require 45 degrees F ambient. It is of paramount importance that gas heaters are provided with adequate ventilation.


Garden shops or Garden Centres usually stock the Belgian type begonia. These are more suitable for the garden and are inferior to the named varieties. The named varieties can be very expensive if mistakes are made and they rot. A very rewarding way, to start growing begonias, is to purchase some Greenhouse Quality tubers from Blackmore & Langdon, as they are only moderately inferior to the named varieties. The latter are selected from thousands of seedlings each year.

Before commencing the growing season, the tubers should be heat-treated by immersing them for 15 minutes, in water heated to 117°F i.e.47°C. This controls leaf eelworm and promotes basal shoots. They should then be transferred to a bath of a cold-water solution of one tablespoon/ gallon of Physan for 2 to 5 minutes. Physan will not kill such insects as Tarsonemid Mite can live on the surface of the tuber. It controls fungus.

After this treatment, which will cause the tubers to awaken from their dormancy, the tubers should be immediately set up in their starting medium. Storing away after this, even for a short time, in peat, vermiculite, etc; will promote rot.

The starting medium is 2 parts grated peat or Soilless compost, to one part washed river sand.

Segmented trays should be half filled with it & then sprinkled with a powder insecticide. The tubers should then be placed on this, concave side facing upwards, (this is the top of the tuber) sprinkled again with the powder and then covered with the medium, to a depth of ¼." A tuber roots around the whole of its periphery. Sybol 2 or Chorophos deter the Vine Weevil beetle from laying its eggs, which would hatch out into grubs and these would eat the roots and tubers.

The trays should be watered lightly and placed on the propagating bench at a temperature of 700F. The centrally heated house kitchen is an ideal place (if the lady of the house permits it!), but a more suitable place is on the propagating bench, fitted with a soil heating cable & controlled by a soil thermostat set at 70°F. This is quite cheap to run, as the cable need only be a 75watt one. A thermocouple type rod stat; is very accurate and the extra expense, in buying a one, is well worthwhile. The top of the propagator must not be totally sealed, nor must condensation be permitted to drop onto the trays. Such conditions will cause the shoots to blacken and rot. Air circulation is a must. The top, if fitted, must be sloped and propped open slightly. Fleece stretched over at night is preferable.

Tubers are notorious in their lack of uniformity in starting to shoot away. In fact, it can be quite annoying to find that it takes some weeks to start up, whilst others, of the same variety, romp away. This is the reason for planting in compartment trays. The early starters can be removed without disturbance to their neighbours.

The earlier a tuber is started, the earlier which heat is required. Therefore - a late February or early March start-up will be more economical. I prefer mid -January as I have some early shows to attend and I also like to take my cuttings as early as possible.

When the tubers have grown shoots of 1" in height, it is time to lever them out of the compartments for potting up. The roots may have grown through the drainage holes, making it difficult to extricate them.

A stiff wire bent at right angles for 3/8", slid down the side of the compartment to the base of the section, turned 90° underneath the root ball and then pulled, removes them without damage.

Tubers grow each year and some are as big as 6" diameter - and more! It will therefore be impossible to start these in segmented trays. They are easily started in half pots or margarine tubs fitted with drainage holes.

Daily inspections of the starting trays reveal the pink eyes peeping through the compost, harbingers of the glories to come.


Greenhouse ambient conditions should be a minimum of 450F
Potting compost should have been mixed and ready for the fray.
Whatever compost chosen - Please beware of the dangers of compost which dry out too quickly and cause the plants to fall over. If a grower is out at work and cannot water more than once a day then such composts will be difficult to take up water.

Beware that the bought in composts have not been stacked outside and been soaked. They will be sour, will not mix well and the plants will not grow away. It is a quite pleasant job to sit and grate some old farmyard manure, on an August day, in the warm sun, in readiness for the following year. It is quite odourless and grates quite easily in the dry weather.
Potting compost.

One bag of John Innes No.2 fresh compost. Mix this with an equal amount of Soilless Potting compost or homemade Chempak Soilless Potting compost. A 9" pot of grated, well-rotted cow manure should be mixed with this. Do not be tempted to use
Concentrated brands of manure, bought in from the local Garden Centre they can burn the roots off the plants.

Buying in sterilised loam you can mix your own John Innes and using builders washed river sand and the peat should be grated

When potting up, approximately ¾" should left between the root ball and the sides of the pot to permit the roots to grow. I know of no other flower that will grow so quickly, as a reward for potting it up, but keep your thumbs out of the way and do not over-firm the compost - lightly pressing it down.

The leaves will now spread out, and in doing so, reveal a wondrous, velvety sheen. This is reward in itself - never mind the flowers that are to come.

The plants must never be permitted to become pot bound. Regular inspections are necessary in order that they may be potted up into larger pots. On the final potting, space must be left between the top of the rot ball and the rim of the pot. This should be approximately 1" to 1½" to allow for topping up with compost, as the roots will fill the pot and appear above the compost. The top of the compost should then be dusted with Sybol 2 or Chorophos. This will, once again, be a barrier against the dreaded Vine Weevil.


Great satisfaction can be obtained by permitting only one shoot to come from the tuber and growing it in a 7" pot, limiting the number of blooms to 6 or 8. By this control of the number of buds, the full potential of the variety can be displayed; otherwise smaller flowers will not evince the true potential of the flower.

Two basal shoots can be permitted in an 8" pot and three in a 9" pot

The choice is then yours. The larger the pot which is used, then the greater space which it will occupy and thus the smaller the number of varieties which one can house.


After the plants have filled their first pots and been potted on, they will benefit from a weekly foliar feed of Sangral High Nitrogen. If the days are dull and damp, delay the spray until a brighter day. The shading must be in place at this time, as the sun will bum the foliage through the droplets of water, which act as magnifying glasses. The resulting brown patches are unsightly to behold and undesirable too!

By mid-June. the plants will benefit from a weekly Sangral Balanced feed into the compost.

When the buds have been secured, the weekly feed should be changed to Sangral High Potash Feed. This is to enhance the size of the flowers. A pinch of Mono Ammonium Phosphate, between finger and thumb, to one gallon of water and watered in, once a week will promote deeper blooms. Flat blooms are unattractive and will be down pointed. If the former feed is given in mid-week and the latter feed is given at the week- end, the plants may not suffer with indigestion!

All watering should be carried out before 10 a.m., but this should not be slavishly adhered to, as the weather will dictate whether the plants require watering or not. Watering is an acquired art and only an inspection of the state of the compost will reveal the plants requirements.


An ideal size of pot in which to exhibit is a 9" one. Three basal shoots from the tuber are required. If there is a surfeit of shoots, the three with their leaves pointing outwards, as near as possible to 120° apart, should be secured to outward sloping canes - (Tied with synthetic string- the string will require checking each week and re-positioned to avoid snagging of the lengthening shoots) - the reason for this is that the flowers produced will point in the directions in which the leaves do and 360° viewing is obtained, although this is not mandatory. 270° viewing will be admirable.3600 viewing with multi-pot classes is wasted. Since the rear blooms are not seen (except by the judge, when he will turn the plants around during his inspections). If the plants are to be shown against a tent wall 270° viewing is adequate.

Timing is not an exact science, but the following method works reasonably well.

My district environment produces flowers some five weeks after the buds are secured at a size of an old 10p piece - 1.125". Variations occur which are caused by the weather and the variety’s idiosyncrasies. Varieties with a greater numbers of petals will take 6 weeks to maturity. This may sound confusing and only experience with a variety, in one’s districts, will produce the correct timing. Varieties with a lesser number of petals mature in less than 5 weeks and edge before then.

However, if the following method is adhered to, successful timing can be obtained.

Make a note of the date of the show to which the plant is going; calculate 4 ½ weeks, 5 weeks & 6 weeks before this date. Pin these dates up on a notice board in your greenhouse, with a colour reference- Say red, blue & green tapes on split canes.

A disc, cut from a piece of white plastic, to the same size as an old 10p piece (1.125") and stuck on the end of a split cane will be the sizing implement

Six weeks before the show, buds that are measured and found to be of this size, should be secured. If they are over this size then choose the smaller bud — the next one in the leaf axle - a younger flower is better than an edged and blown centred one. Buds are produced in weekly sequences from the leaf
axles. Do not be soft hearted and leave the oversized buds on - you will regret it!! Do not touch or damage the buds. Any buds produced before the planned date should have been removed.

Call this Red selection and use some electrician’s tape to make a flag, stuck on a split cane, to be stuck in the side of the pot, to let you know that this is the 6-week stop.

Repeat this for the 5 weeks stop with say, a blue flag and also for the 4½weeks stop with a green flag. The selection of the buds MUST be on the exact day 4½/ 5/ 6 weeks before the show day. The buds are really moving quickly and a day’s variation will give the wrong size for timing.

One week after, (Week No.1) - each of the three selections; in sequence,- nip out their following buds, which are produced behind the selected buds - taking care not to damage the selected ones.

Again, one week after this, (Week No.2) nip out the growing tips of each flower-producing shoot. (After each of the timing selections) This is done to channel all of the plant’s energy into the selected flowers. It is also to ensure that the flowers are produced above the leaves and ensure that the leaves do not impede the view of the mature flowers. This nipping out of the growing tips should be carefully done, so as not to damage the selected buds. It should also be done when the side shoots are small and then there will be no visible scars.

The value of the use of the coloured flags is now apparent, as each plant can be identified - without searching around for the plants and handling them.

Week No.3 (In weekly sequences for the three stoppings.)

The selected buds will be growing much larger now and the telescopic supports, purchased from the N.B.S. or Messrs. Blackmore & Langdon, should inserted, in such a manner so as to miss the tubers, avoiding damage to the leaves, flowers and branches. This is a NERVE RACKING exercise!! Care is of the essence. The support’s stainless steel adjusting spring clip and the “U” shaped plastic bloom support are the culprits. They can easily nick the buds and leaves. Their positioning should be so that the support will point the bloom in the direction required and the plastic “U” should fit snugly- but not tightly behind the bud. They should be inserted from the top of the plant, with a steady hand and your nose above the track through the foliage where they are being inserted. The supports will require adjusting once or twice a week so as to keep the bloom positioned and upright. It is advisable that all supports should be checked for free movement before inserting them. A sticking support can cause untold havoc when manipulating it in the foliage. Blooms can fly over one’s shoulder if a sticking support suddenly frees itself and moves with uncontrolled vigour.

From now on it will be necessary to nip out the side buds, which grow from each side of the selected buds. Some are female flowers (single and seedpods behind them) whilst others are male double flowers. It is safer to use a pair of elongated fine scissors for this purpose. The bloom supports will steady the buds during this operation. The small pieces of stem left behind, will drops off within a week and will require removing.

Week No.4. (In weekly sequences for the three stoppings)

Leaves, which are impeding the positioning of the buds, should be removed, as close to the base of the stem as possible, carefully avoid damaging the blooms, as they are withdrawn through the structure of the plant. If this is not possible - remove the leaf at the top of its stem and be vigilant to remove the stem as it detaches from the base some 6 to 7 days later.

At the end of the fourth week, it is time to “engineer” the structure of the plant. Using soft synthetic green string (not the bright green kind!) pull the supports together-or away from each other, using the canes as straining posts. The idea is to show each bloom, positioned at equal distances and certainly not covering each other or with large gaps. If a bloom (or blooms) has runny colours, is blotched, marked, damaged or has a bad centre then REMOVE IT. The balance has then to be adjusted so as to fill in the gap(s)

Weeks No.4½ & then for 5 weeks & 6 weeks timing. in turn.

Feeding must now cease. A balanced plant should have its leaves down to the edge of the pot, with no ugly leafless stems in view. The above “engineering” is still in progress and it may be necessary to remove a support or two, in order to re-insert it in a better position.

On the eve of the show, all of the supports should be snugly fitted, securely - not too tightly. The cotton wool (preferably the synthetic type, which is springy) is then inserted between each bloom and the adjacent leaves, between bloom and bloom, in such a manner so as to prevent their movement. The centre of the plant, at the top, should also be packed with cotton wool. Movement in transit should be kept to a minimum.

Blooms can be carefully moved aside by means of forming a “V” with two fingers, behind the bloom, with its stem in between the fingers, the bloom is moved aside slightly and the cotton wool carefully pushed in - from behind the bloom — not from the front!

Carrying boxes are a must, with a base of approximately 18"x12" to prevent tipping over. The longer side should face the direction of travel, which will give stability. They should be made for the size of the pot, which is to be transported and spaced apart in the van/ car so as not to permit them to slide and rub themselves on each other or against the sides of the vehicle. The boxes should not allow the pots to tip over- should there be sudden braking. Care taken now, is better than heartbreak at the show ground. They should have had a good watering before setting off.

Additional pots, in their boxes, should have spacing between the boxes- and between the boxes and the sides of the vehicle to prevent their movement and the touching of plant against plant.

Arrive in good time so as to find a staging table, leisurely remove the cotton wool, and remove any damaged blooms or any blooms, which may have blown their centres.
Supports will require readjusting and the ties may also require attention. Spare supports, string & scissors should be in your kit. Remove any damaged or yellow leaves.

Turn the plant to show its best side. If it is a multi-pot class, boxes or packing plinths, of various heights, painted black should have been prepared before hand and they are placed under the pots so as to present a balanced triangle (3 pots) or banked evenly for more that three pots. All pots should be wiped clean and clay pots should be free of algae and white marks.

Are you happy with what you see? Look at the competition. Can you substitute a weak pot with a better one to win that class? Then, the weaker one may win in another class? Go to It! Fit some name labels and the class entrance tickets. Hang around until they throw you out for the judging - last minute attention is invaluable.
If some one has beaten you, ask the judges to explain where you went wrong, inspect the winner’s exhibits and learn from them, determined not to repeat your mistake next year.

What a judge is looking for.


i) Flowers and foliage should appear fresh with no edging to either flowers or foliage.

ii) Flowers should be facing forwards - upright or drooping.

iii) Back petals should be showing no signs of scorching.

iii) All petals should be present; no signs of trimming or petal removal should be visible.

iv) Leaves clad to the top of the pot.


i) Mildew or disease - any plant showing visible signs of these should be removed by the stewards from the show bench and not judged. The exhibitor should be diplomatically informed as to the reasons, in that it could be spread to other exhibitor's plants.
ii) Stem rot is due to poor cultivation and attention and should be judged accordingly.


Flowering plants

i) Flowers should be symmetrical in shape (round).
ii) Multiple centres should not be present to any flowers.
iii) Flowers should be equally spaced around the plant, not overlapping each other.
iv) The plant should be in balance.
v) The top of the plant should preferably be full with flowers, not open.
vi) Colour run or blotching should be avoided if possible, points will be lost if present.
vii) Leaves should not be marked or yellowing.
viii) Foliage should commence at the pot level with no bare stems showing removal of foliage,
ix) The size of the majority of flowers to the plant, should commensurate with the variety, judges should take into consideration exceptional sizes of flowers known to be normally small, and should judge accordingly.
x) Each main stem should preferably be carrying side shoots, with at least one flower which should be fully open; the main stem should preferably be carrying three flowers
xi) Picotee edging should preferably be sharp and clear.


Apricot DelightSuperb Branching, sturdy, loads of petals in the blooms and leaves down to the edge of the pot.

City of Ballaarat.Good branching habit but slightly short of petals & it matures in less than 5weeks.

Roy Hartley.Superb big deep pink blooms – may give leggy and leafless stems in not grown correctly

Sweet DreamsBranches well but the blooms are not as deep as Roy Hartley – but there are plenty of them.

Fairylight.Branches well, there are loads of them in fact and they require limiting.

Elizabeth Lee. This is a sport of Fairylight with lemon ground. Treat the same as Fairylight.

Beryl Rhodes.This is a biscuit coloured bloom and it is another that tends to have leafless stems above the pot. It requires managing.

Jessie Cruickshank.A delicate white picotee with endless branching and it is ideal for all round viewing. Limit the number of blooms for good size and depth.

Jennifer Wilson.This grows short and it is a humdinger if grown in light condition to enhance the picotee edging.

Fiona Ramsay.It is a pink bicolour, branches well and it is easy to grow.

TahitiIt is a good orange – so long as the flowers are turned towards the glass. This discourages the white centres inherent in its makeup.

Coppelia This is a clear white picotee – an eye catcher and it branches well.

Ziggy a refined white picotee with marvellous bloom form

MoonlightAn ethereal cream with a rosebud centre and it is positively impressive.

Launcelot.A lovely white with a rosebud centre, strong and prolific branching – a winner.

Rachel AnneIt is a clear cream picotee with all of the attributes for a good pot plant.It is a great improvement on Gay Gordon.

Mrs. E McLauchlanA pink bicolour with rosebud centres, superb form, branches wonderfully and it is a beauty.


I have already mentioned the steps to avoid Vine Weevil, but a good precaution should be the watering in of nematodes - sold in most garden centres. This should be carried out in early September. Armillatox sprayed onto the top of the compost in each pot each week is a deterrent an it is easy to apply.

If corky scabs appear on the leaves, it is probably Tarsonemid mite. It can be treated by spraying with green control nematodes. Should they not be treated the plants will require removing from the greenhouse and there is no chance of showing them that season!.

Prevention is the better part of growing. There are some pesticides which will eradicate and prevent the pest and this can be applied at the tuber state too.

Diseased plants must not be taken to a show. Judges will have them removed from the benches.
If leaves are being eaten, this is certainly due to caterpillars. Defenders sell Dipel, which can be sprayed on and kills the pests by starvation — the mouth and gut muscles are paralysed.

Yellow flytraps, hung in the greenhouse at the beginning of March, will take care of those annoying small flies-sciarid fly- (and others). Defenders also sell Hyposure - a mite that will see them off.
Provado is a fairly new product and it is used as a drench – when the plants are in a full growing state. It kills vine weevil, green, white, black and sciarid fly. The latter is a real pest emanating from peat products.

White deposits on the leaves evince mildew. Systhane is an excellent spray but it leaves white deposits on the leaves. It can be washed off but black spots are still present in the curing of the mildew. It is therefore best to spray as a deterrent.

Some of the troubles may be imported after the growing season has started i.e. from plants that have been received from friends. Always give these new plants the same disinfecting before bringing them into your greenhouse. Quarantine them for a while.

If your plants are healthy before a show then do not place them back into the greenhouse until you are sure that they have not picked up some pest.

Happy and successful growing.
Derek L Telford