GROWING FROM TUBERS
As with seedlings the seed compost used as the starting medium should be prepared well in advance to allow it to warm up. The starting date will vary according to the size of the tubers and when they are to flower. A large tuber will take approximately 22 weeks from starting to flowering and a cutting tuber a month or so longer. This is only a rough guide as some varieties take longer to start than others. Tubers can be boxed up as soon as the compost attains the optimum temperature of between 65 and 70 degrees Fahrenheit. Boxes about four inches deep will hold enough compost to accommodate a good root system. Care must be taken to ensure the tubers are inserted the correct way up. The top of the tuber can be recognised by the scar left from the previous year's growth. Sufficient space for the root system to develop must be left between each tuber and the number per box will therefore be dictated by the size of the tubers. Great care must be taken at this stage not to overwater or tuber losses will occur; if tubers are watered in and the boxes covered over with sheets of paper no further watering will be required until growth has started.
Once the root system has developed sufficiently, tubers should be potted into a potting compost, normally when around two inches of top growth can be seen. The size of pot chosen depends on the rootball, one with a diameter one inch larger is ideal, as in this way the risk of overwatering is lessened. Fill the pot around half full of compost and put the tuber in the pot. Fill to around one inch from the top of the pot, this time completely covering the tuber (roots are produced all over the tuber), firm and water in. Further watering will not be necessary until the pot is nearly dry, about two weeks later depending on growing conditions. Any holes left where the tubers have been removed from the boxes should be filled with seed compost to allow the remainder to develop. After they have been potted the plants can then be moved to the open staging and grown on at a temperature of 50 degrees Fahrenheit.
Foliar feeding will help plants to grow on steadily and provide the necessary humidity. At this stage it must be decided how the plants are to be grown and a range of different options is available. The choice with cutting tubers is not difficult as normally only one shoot is produced, but older tubers will produce more and depending on the way one wishes to grow the plants it will have to be decided which to retain and which to remove as cuttings. As soon as the root system of the plant reaches the edge of the pot it requires potting on. This is not a difficult operation if a few simple steps are taken. A pot two inches larger will be required; fill the bottom half of the pot with compost (if a clay pot is used it must be well crocked), remove the plant to be repotted from its pot, then insert the smaller pot inside the larger pot and pack round with compost. (If the compost is not firmed well at this stage growth will be rapid but plants will be soft, which can later lead to stem rot. A more balanced growth is looked for which in turn will lead to better quality plants and hence to superior blooms). It is then simply a matter of removing the smaller pot and inserting the rootball into the space remaining. Often this is the final potting but if a plant is particularly vigorous or a large specimen is required, a third potting may be required following the same procedure. After the final potting all plants require staking.
Any side shoots which will now be produced that are not required can be removed as cuttings, letting the plant channel all its energy into the main growing stem(s). The first two buds produced on each stem will not give a true representation of what the plant is capable of and should be removed. This will allow the plant to develop sufficiently to carry the flower(s). A begonia produces more than one flower per stem, normally consisting of a central male flower flanked by two smaller female flowers (recognisable by the seed pod at the rear of the flower). If left alone, the female flowers will develop into small single flowers, but to allow the male flower to develop its true potential these should be removed as soon as they are large enough to handle, using a simple twisting motion. At this stage of growth the plants roots will be showing at the surface of the pot and each pot can be given a top dressing with the compost used for potting. This will help to feed the plant and utilise the additional roots. All foliar feeding must now cease and a much drier atmosphere needs to be provided with plants receiving as much ventilation as possible. One more additional task must be undertaken at this point. Because of the size of the flowers, plants must be properly staked and the flowers given some sort of support. The begonia supports specially designed for this purpose will help show the blooms to their best advantage.
After the flowering period is past plants must not be left to go to rest. Watering must not cease until the plants begin to die back of their own accord (foliage turns yellow). Too many tuber losses can be attributed to cutting the water supply too soon from the plants. Watering is a very important part in the process of ripening the tubers for their winter rest. If tubers are not ripened properly they will shrivel up in storage. A feed of a high potash fertiliser will assist in the ripening process. After the foliage has fallen off and the last piece of stem has come away from the tuber, the tuber can be removed from the pot and most of the old compost cleaned away. The tubers can then be put in boxes, labelled and left on top of the staging. After about two weeks the remaining roots will have died away and the tubers can be given a thorough cleaning using a soft brush. Care should be taken not to rub the skin off the tuber during this process as roots will not grow from any damaged areas the following year. The last remaining task before storage is to remove the scab which forms where the old flower stems came off. If this is not done rot will start which will eventually destroy the tuber. Once it is ready to be removed the scab will come off easily using the point of a knife or a thumb nail and the tuber should then be dusted with sulphur powder to prevent infection from setting in. The tubers are then ready for storage. Older tubers can be placed singly in boxes, one layer only in each box; making inspection during the winter a simple process. Cutting tubers are often better left in their pots, but if this is not possible trays of almost dry compost will provide an alternative. The storage area should be dry and frost free, but not too warm, a temperature of between 40 and 45 degrees Fahrenheit being ideal. Much warmer than this will start the tubers into premature growth and make them more prone to shrivelling. Tubers should be inspected at regular intervals, any rot cut away and the wound dusted with sulphur powder.