Growing Begonias
Tuber Hybrida Begonias
There are many different plants in the species of plants called begonias and members of our group are mainly interested in growing tuber hybrida begonias. The information below is accordingly written with this in mind, and may not be appropriate for growing other types of begonias e.g Rex begonias and rhizome begonias.
Growing Begonias
Buy your tuber from a reputable grower; the price can vary widely with prices for the specific named varieties being the most expensive.
As soon as you get your tuber which can be as small as your finger nail, plant it in a 50/50 mixture of potting mix and pumice or vermiculite with the top half of the tuber above the level of the mix, keep moist but not wet and place in a warm area. The tuber should start to develop shoots any time from late September to late November.
When the shoots are about 2 cm long the tuber should be planted to a depth of around 2.5 cm in a good quality potting mix that has good drainage. It is always tempting to buy potting mix based on price, but cheap mixes are some times not sterilised, and may contain diseases which begonia tubers are susceptible to. Also the quality of the slow release fertiliser will likely be lower.
Again keep the mixture damp not wet, as in the early stages the tuber will have few (if any) roots to take up moisture. Wet soil is a big contributor to rot in begonia tubers. Letting the soil get dry between watering is preferred to over watering.
Begonias grow best in a pot where the roots are a little crowded, so it is preferable to start them in a small pot up to 10cm diameter, and then transplant them into a 20cm pot later. If the tubers you have are small it is essential you do this as small tubers rarely grow well in a big pot and often rot, as the moisture content in the large amount of potting mix is too much for the tuber to cope with.
When the shape of the plant has been established it will require staking, care should be taken to use a soft material to tie the plant as the stems are easily damaged and this is the most likely place that rot will start. Care must be taken when inserting the stake into the mix not to damage the tuber, as this may cause the tuber to rot. If there are several stems to support one stake may not be enough and in this instance it is preferable to use two or more stakes.
Do you need to use fertilisers? This subject is very much a matter of opinion, as growers do not all have the same objective in growing there plants. Many growers who do not want to specficly produce a bigger plant and huge flowers use a good potting mix with 6 month slow release fertiliser, and do not feed the plant during that season. If however you do not want to invest in the more expensive potting mix, Phostrogen is a good all round fertiliser.
If the tuber develops too many shoots some may be removed and the area dusted with Flowers of Sulphur. These shoots may be used to produce another tuber. Standard plants that have a lot of shoots are hard to manage when the stems get bigger and produce flowers, so removal of excess shoots when they are small will save you a lot of work later and help you to keep your plant looking good.
When the Begonia is in flower the female flowers that appear on either side of the male flower should be removed from standard begonias, as this enhances the growth of the male flower and consequently the display. DO NOT do this with the hanging varieties.
At the end of the season in April/May give a final watering with Sulphate of Potash and remove all flowers and growing tips, and let the plant dry out. The timing of this process will depend on whether the plant is earlier or later flowering. Lay the pot on its side to let the stems fall off as they dry out. When all the stems have fallen off remove the tuber from the potting mix and dust the areas with no skin with Flowers of Sulphur. Store the tuber in a dry frost free place for the winter, Inspect regularly for signs of rot or insect damage. (See also below*)
Dealing with Begonia Problems
Begonia problems and diseases is a subject many people have written about, and there are many and widely varying opinions as to how you deal with the problems. Personally I do not use sprays as I have found over the years if you spray for one pest another seems to arrive to take its place. My policy is to aim for healthy well feed plants grown in good growing conditions. This means not only good potting mix, but an airy uncrowded position with some shade particularly in the middle of the day. Sure I do get some bugs attacking the leaves, but if the plant lives on well otherwise I do not see any point stressing about it. Where I do however find the caterpillars on the leaves they do not survive.
*Where diseases have been a problem during the growing season, it is generally preferable to treat the tubers to minimize the chance of diseases wintering over. There are many opinions as to the best way to do this, and I treat my tubers as follows.
1. After removing the tuber from the potting mix, brush the tuber with a soft paint brush to remove any dry potting mix from the tuber, taking care to not damage the skin.
2. Soak the tuber in a solution of Janola (1:80) for 10 minutes.
3. Rinse the tuber in clean water
4. Dry the tuber in a well aired area. This is important as any moisture left, may be enough to start a rotting process.
5. Dust the scabs where the stems have fallen off with flowers of Sulphur or some propriety brand of treatment for mould
Tarsonemid Mites
During the 2018-2019 season, this pest was prevalent in several parts of the country, and there have been smaller outbreaks since. It is less than 0.5mm in size and can only be detected with magnification (10x). Further information is shown in the links below. There are however steps you can take to minimize getting the problem or spreading it.
1. New plants coming on to your property should be isolated from your other plants for at least 3 weeks
2. Keep other host plants away from your begonias- cyclamen and strawberries for example.
3. If you have got mites remove damaged stems and flowers from your plant and isolate the plant
4. Spray with an appropriate mite spray.
5. The mites can winter over in soil, so at the end of the season clean your tubers as above and sterilize your pots
6. Dump your old potting mix, and do not reuse it or compost it unless you can sterilize it.
There are numerous sites you can access by searching Begonia problems or Begonia Diseases, and I have listed three below which should help in your search for answers.
Calvin Berg Web Master
http://www.national-begonia-society.co.uk/Editors%20Tutorial/ET_Pests%20&%20Diseases.htm
http://extension.psu.edu/pests/plant-diseases/all-fact-sheets/begonia-diseases
http://www.herbs2000.com/flowers/bg_pest_dise.htm