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The Editor's Tutorial

.Beginners

Further and more detailed information can be found in the
FULL TUTORIAL
Start by viewing
THE BASICS

Masquerade

REQUIREMENTS
Greenhouse with shading and plenty of ventilation in the summer and some heating to maintain 45°f. 8ºc  minimum in the early part of the season.  
Heated propagator.  An electrically heated propagator is ideal for starting a small number of tubers and also for rooting cuttings.
Tubers. Like many things in life if you want the best you have to pay for them and the best commercially available exhibition tubers are not cheap, expect to pay £10 - £20 for a dormant tuber, £30 for new introductions.  This can be expensive for a beginner, so a cheaper alternative is probably preferable - if you can find a source.  Tubers available from garden centres etc. do not have the potential to give the same results as named varieties. 
Compost.  Most growers in this area use a soil-less compost, the favourite being Scotts Levington.  

Procedure.
SUITABLE COMPOST  +  GOOD TUBER  +  RIGHT CONDITIONS
and
DOING THE RIGHT THING AT THE RIGHT TIME
will give a
GOOD PLANT
that will produce
GOOD BLOOMS
Starting the tubers in mid March will have them in flower by August.
The procedure must not be rushed, the plants will need potting on twice or perhaps three times and should be in their final pots for three weeks before the buds are allowed to develop.  

The top of the tuber can be identified by a hollow or a scar where the previous year's stem grew.
I prefer to start the tubers individually in half-pots but trays are quite acceptable and probably the most used method.  Whether you use pots or trays it is important to completely cover the tubers (just under the surface).  Roots grow all over a begonia tuber, if you only half cover you are losing half the potential root system, also the exposed area will become hard and corky, denying the opportunity to grow roots another year.

Irish moss peat is mixed to the compost in equal portions for starting, water is added before use, just sufficient to make it cling together but not so much that it becomes sodden.  Using tepid water will bring the compost up to temperature.  Here on the South Coast of England tap water contains an element of lime, this suits begonias. 

An electric propagator is ideal for starting,  a temperature of about 70°f. 21°c. is required. Once green leaves develop the top can be removed during the day to encourage sturdy growth.   Tuberous begonias are very erratic starters, it is quite common for some to be in green leaf before others are even pipping.
After a few weeks with top growth about 2½" 6cm the plants will be ready for potting on.

Do not wait until the roots have become pot-bound, move the plant on into a larger pot again pre-mixing water to moisten the compost.   No further watering will then be required for two or three days.
Note the root growth of the plant shown here is vigorous but the top growth compact - just right in my book !  

Once the plants are out onto the open staging a minimum temperature of 45°f. 8ºc should be maintained, preferably a little above this, but high temperatures should also be guarded against as this will lead to forced leggy growth. Double bubble insulation will help to keep fuel bills down.
Give as much ventilation as possible when the weather permits. 
After about five weeks the roots will have reached the sides of the pot again and a further potting on is necessary. 

Until the plant is fully grown all buds must be removed, even the finest varieties will produce poor blooms from early buds.  As a general rule the plant should be 3 weeks in its final pot before the buds are allowed to develop.

When final potting insert a stake as close as possible behind the stem and tilted back about parallel to the side of the pot, then when the blooms open they will be above the centre of the pot.  Draw the stem back gently using a tie that will not cut into the stem.  Take care not to damage the root system when inserting the stake.  Continue removing buds for about another three weeks.

At last the flowers are allowed to develop, a smaller bud can be seen to the side of the main one, these are pinched out as early as possible to allow the full resources to be concentrated into the main, central, bud.  It is also beneficial with varieties that have short flower stems  to remove any excess leaves that may obstruct the flowers when they are fully open.

Even the very finest varieties may only produce insignificant blooms if they are allowed to come into flower too early, by three weeks after final potting the pot will be nicely full of roots but not completely pot-bound.  Watering should be increased to keep the compost moist at all times, but not saturated.   Feeding at half strength every other watering can now begin. Use a high potash feed such as Phrostogen or Chempak no 4.

The length of time that a bloom will remain at its best is governed by conditions and the weather.  This bloom is "over the top" it is past its best.  Very high temperatures make the buds blow open too quickly and flowers deteriorate prematurely whilst wet weather causes blooms to damp off.
Premature damping will also be caused by too much humidity.  Although it is beneficial to damp down the greenhouse floor and staging (on warm mornings) whilst the plant is growing this must stop once the flowers begin to open.

As Autumn approaches the plant will show signs of tiredness, flowers will be appreciably smaller and leaves will begin to yellow.
In order for the tuber to build up it's resources in preparation for dormancy all late flowers should be removed and the growing tips of the stems pinched out.  Think of the tuber as a battery that needs recharging.  Watering should continue at a reduced rate. 

By late Autumn only the odd stem will remain and by this time the compost should be almost dry.   Once the stems have fallen the tuber should be left in its pot for two or three more weeks to allow the skin to ripen, then it can be harvested (removed from the pot).  When removing the compost take care not to tear off any skin as roots will not form next year on the damaged area.

At the base of where the stem joined the tuber a scab will have formed, this must be removed as rot will form underneath and eat down into the tuber.  The scab can be prized off quite easily when it is ready.  The wound will dry naturally but the tuber should not be stored away until the wound has healed. After the tubers have dried  they can be stored in almost, but not completely dry Irish moss peat.  If the peat clings to the tuber it is not dry enough.   Inspect the tubers every two or three weeks.

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