The National Begonia Society



The Editor's Tutorial

.Through the Season

   Before the new season starts, which for me is in early February (except for seed which I start in the kitchen in mid January), there is a good deal of preparation that must be carried out.  The greenhouse has to be thoroughly cleaned and given a liberal spray of Jeyes fluid, sandbeds and propagators receive the same treatment and all pots are washed in a solution of the same product. ideally I prefer to clean all my pots when the tubers are harvested.

    There are a vast selection of proprietary composts on the market, both loam based and soilless and countless "special" recipes for those who prefer to mix their own.  Here on the South Coast the majority of growers, myself included, use Scotts Levington Professional Composts, available from gardening clubs and some garden centres.
    Basically the idea is to start off into something weak and final pot into something strong (but not too strong).  The first contact that my tubers have with compost in the new season is in a mixture of 50% Levington F2 and 50% Irish moss peat.  
    Before using any compost/combination of composts I always mix thoroughly in a bucket, adding just sufficient water to make it cling together, then no further watering is given directly after the plant has been potted.  Using a dry mix then watering on top can clog and cake the surface thus denying roots the opportunity of access to air. 

A heated propagator is ideal for starting a small collection,  growers with larger stocks usually prefer a heated sand-bed.  In either case a constant temperature of about 70f. 21c. should be maintained. Tuberous begonias are very erratic starters, some may have their first leaves before others have even pipped.  For this reason I prefer to start my tubers off individually in half-pots.  Many growers place several together in trays but to my mind this may cause problems as developing roots can become entwined.   My method ensures that roots are not disturbed or torn when being potted on.
    Whether you are going to use trays or pots it is important to completely cover the tubers (just under the surface).  You may well have seen pictures in gardening magazines of tubers half covered or worse still sitting on top of the compost.  This is entirely wrong.  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.  The top of the tuber can be identified by the scar where the previous year's stem developed from.
    In the propagator or hotbed the warmth is coming up from underneath, so the surface of the compost may seem moist but in fact beneath it can be very dry - and this is what a good percentage of the roots will be growing into (or rather not growing !).  It may well be sufficient to only water at four or five day intervals but it certainly needs checking more often than this.  Here, ii my opinion, is another case for starting in half-pots.  The pot can be lifted out to view the condition of the sand underneath and even the plant eased out of it's pot.
    The point that I am trying to make is that the compost that you can't see is the most important part.

    Once the first leaves have developed and, more importantly, a healthy root structure is underway it is time to move the plants out of the propagator or hotbed and at the same time into a larger pot (or into pots for the first time if you have started the tubers in trays).  Do not overpot, an example would be from 3" 8cm. diameter to 5"12cm. The policy being to move the plants on as the goodness in the compost is beginning to become exhausted and the roots reach the sides of the pot.  My chosen compost, Levington M3 is not taken straight from the bag but first mixed in a bucket to break up any lumps, adding sufficient water to make it cling.  Having ensured plants to be potted on are well watered no more is then given for a day or two (unless it is very hot). 
Now that the plants are out of the propagator or hotbed and onto the open staging a minimum temperature of  45f. 8c has to be maintained, double bubble insulation will help to keep fuel bills down.  Growth is very vigorous at this stage and should not be retarded, these temperatures should be regarded as absolute minimum and a few degrees higher is preferable.  Equally important is not to induce forced growth, what we need is sturdy, stocky plants, at every opportunity afford as much ventilation as possible, trying to avoid high temperatures.  On warm sunny mornings an occasional spray over the foliage is beneficial, but the leaves must have dried before the temperature drops. Our seasons are changing and it now seems necessary to apply shading ever earlier in the year, begonia leaves are very susceptible to sun scorch.
Even at this early stage buds can develop, these must be removed.  The onset of (hopefully) warmer weather can also herald the arrival of unwelcome guests into the greenhouse,  white fly, thrips and mite will all cause damage and need to be dealt with by spraying with a suitable insecticide.  Test on just one leaf and wait for at least one week if using a previously untried spray.  Smoke cones also offer a possible prevention.

    Ideally for me this is in early June, giving three weeks before the buds are allowed to develop for our Show.  The compost is again Levington M3.  Leave room between the top of the compost and the rim of the pot for a top dressing, it is a good idea to fill the new pot with compost using the old pot as as a former.
This is a convenient stage to insert a stake to support the stem, placing it as close as possible behind the stem and tilted back at an angle about parallel to the side of the pot, then when the blooms are open they will be above the centre of the pot, lessening the possibility of the plant toppling over.  In the case of multi-stemmed plants facing all around (a specimen plant) then the stakes need to be in front of the stems and positioned more upright.

    3 weeks after final potting the buds can be allowed to develop (at last!).  The plant is now fully grown and capable of bearing flowers to their full potential.  Up until this time all buds have to be pinched out, this is to channel all resources into the plant itself which in turn will support the blooms.  Watering must be increased to keep the compost moist at all times, but not saturated.
Now is the time to apply a top dressing filling the pot right up to the rim. Roots will delve into this giving the developing buds that little bit extra.  Feeding can now commence, strength at every other watering.  Chempak No.4 is ideal.
    Damping down of the floor must cease and maximum ventilation maintained, a fan to give additional circulation is beneficial and many growers remove some lower panes of glass. Additional shading may be needed to try and keep temperatures down.

    A decision needs to be taken quite early in the season on how each plant is to be grown, whether or not exhibiting is the aim.
 To a degree the plant makes this decision for you, if it  has two or more stems of equal size then there is the opportunity of a multi-stemmed plant, but if the leaves face in towards each other the blooms will also face inwards.  In this case it is best to remove some stems, they will not be wasted as they can be used for cuttings.  Always leave the strongest stem to grow on.
    To build up stocks of a newly acquired variety it is best to grow it as a single stem plant, taking others off for cuttings.  Better still is to grow it as a "cut bloom" plant, here just one bloom is grown on a stem, all side shoots being taken off to increase stock.  This method often causes the tuber to sprout more shoots part way through the season - even more cuttings !
    An ideal and very popular way to grow  begonias is as "restricted pots" and there are special classes for these at begonia shows.  The maximum size of pot is 7" (diameter) and the plant must have only one main stem.  Advantages here are that any surplus stems can be used for cuttings, it does not take up too much space in the greenhouse, the fully grown plant can still be transported in a car and because all the blooms face one way it makes a very acceptable addition to any mass display.  

    If you are intending to exhibit at a Show then the weeks leading up to it are critical, especially concerning the weather, which of course we have no control over.  If it is too hot the blooms will come out too early and "blow", if it is too cold they will not be open "on the day".
A damp atmosphere will edge the blooms prematurely.  Ideal conditions would be dry, bright and cool to warm, about 70f 21c.
    Here on the South Coast cut blooms need about five weeks from a bud the size of a 20p coin to reach their optimum. Varieties, location and individual set-ups will vary this, the only way is to make notes.  Above this selected bud the growing tip is pinched out, (this is known as stopping) if the bud is too small at this stage then the one below is left as an insurance, giving the choice of two.  A leaf above the selected bud is also retained to help pull the sap up to the bud.  As the five weeks before date approaches ease off on the pinching out of buds, you can always take another one off but you cannot add one on.
    Pot plants are best left to three weeks (to the Show) before they are stopped  the largest bud should be 3"-3" 75 - 90mm.   Leave the next two and pinch out above this, same procedure for all stems and side shoots.  Some leaves may well need removing to allow space for the blooms when they are open, try to visualise the begonia in full bloom.  My plants always look very bare for a couple of weeks when this has been done  but it is worthwhile. 

    A top exhibitor once said "any fool can grow them but it takes an expert to get them to the Show". Unfortunately damaging plants in transit is an all too regular occurrence.  Over the years at Southsea  we have evolved a system that we believe to be as good as any.  The pots are stood in rectangular plastic containers and firmly packed around with small sand bags and bricks, the containers are then kept apart in the van by more bricks used as spacers.  The weight of the bricks gives the van a cushioned ride.  The plants' blooms are held by special adjustable supports and further protected by cotton wool or tissue paper.
In addition to exhibiting pots there are also classes at begonia shows where only the cut bloom is entered, and this has obvious advantages when it comes to transporting.  The blooms are taken to the Show in boxes and staged on special boards containing paper cups.  There are classes for 12, 6, 3 and 1 bloom.  Once cut some varieties deteriorate much quicker than others and it is quite common on the second day of  a Show to find blooms that are well past their best.  

    Plants that have been "stopped" for a show can only produce one flush of blooms but those grown for a continuing display will carry on flowering well into September albeit bearing smaller blooms. In order for the tuber to build up resources in preparation for dormancy all late flowers should be removed and the growing tips pinched out.  Think of the tuber as a battery that needs recharging. 
    As the leaves yellow and fall reduce the watering so that by the time only the stem remains the compost is almost, but not completely dry.  The stem should not be forcibly removed, when it is ready it will drop of it's own accord or come away with a very gentle tug.  Soon after this the tuber can be harvested, washed and inspected, this will be the first time it has been seen since starting back in February/March.  It should have increased in size, perhaps by as much as 30%, but some losses will inevitably occur.
At the base of where the stem joined the tuber a scab will form,
this must be removed to prevent rot from forming under it.  When ready it can easily be prized off.
    Although the main tubers may well have lost their stems it is an advantage to try and keep the cuttings growing on as long as possible to increase potential tuber size and reduce dormancy time. Small cutting tubers start to shrivel after about four weeks.

    Having dried, inspected, removed the scab and any rot, the tubers are ready for storing.  I always use Irish moss peat.  It must be almost completely dry before use, the tubers are then stored in buckets and placed in the loft.  After a week they are inspected, if the peat is clinging to the tubers it is not dry enough and is spread out for a few more days.  Further inspections are carried every three weeks.