Rex Begonias by the late Hugh McLauchlan
The first Begonia rex arrived in England in 1856 according to one account accidentally in a consignment of orchids from Assam in North East India. It was auctioned in London and bought by a Belgian commercial horticulturist who crossed it with several other Begonia species to produce some exciting hybrids. The beauty of the leaves was, and is. the outstanding feature of the Rex-cultorum Begonias and this led to such descriptions as the following which appeared in a 1911 catalogue.
‘Nature has bestowed on Rex Begonias many of her choicest gifts, uniting the radiance and brilliance of precious jewels. The shining lustre of metals and the beautiful colours and textures of the most costly fabrics, the leaves alone possess all these charms while the dainty flowers add lightness and grace’
To get the best out of these plants they must have the right conditions. The correct light levels greatly improve the colour and the lustre of the leaves and, like most other Begonias, they prefer filtered light not direct sunlight. A popular site is under the staging in a greenhouse as this is usually a good position for humidity, which is also high in their cultural requirements. If lighting is insufficient, fluorescent lighting will greatly enhance their colour.
Rex Begonias like to be kept moist when in full growth and must not be allowed to dry out, but never over water as this can induce rot in the rhizomes. A well drained compost is essential. I have no problems with Chempak potting compost to which I add coarse grit and a little Perlite. During the growing season I feed regularly every second week with a high potash feed at half strength. Re-potting should be done during the growing season but avoid over potting. Pots should be turned regularly to ensure uniform growth. I find that Rex Begonias do better in clay pots because of their porosity. Plastic pots can be successfully used if over watering is avoided. During the growing season temperatures ranging from 70F to 75F are ideal for Rex Begonias. Over the winter lower temperatures are often inevitable. At such times watering should be reduced and the use of fertilisers discontinued. Draughts and sudden temperature changes will certainly harm these Begonias.
Over winter my Rex collection is housed in a large terrarium with under-soil heating and a sliding double glazed door to avoid temperature fluctuations and draughts. Good air circulation is essential. Watering should be done at pot level and the leaves kept dry to reduce the risk of mildew. As a safeguard I spray lightly and regularly with Nimrod T early in the morning to ensure that by nightfall all the leaves are dry.
Propagation by leaf section is the usual method and has a high success rate. Rex Begonias come in three leaf sizes: miniature, medium and large with sizes ranging from 2” to 14”. With miniature leaves the whole leaf will be used with the stem cut to around 1∙5”. Larger leaves can be pinned down on the compost again with a stem of 1∙5”, the veins cut on the underside and treated with hormone powder. Contact with the compost can be achieved with pebbles or wire staples. Rooting should commence in about three weeks in a propagator at about 70F . I now use the new coir compost made from coconut fibre now being introduced to replace peat. I first saw this in use at Glasgow Botanic Gardens and the success rate has been 95% to 100%. It is very clean to use, completely sterile, very fine and easily kept moist. I have also used it for the rooting of Chrysanthemums and Dahlias and am now using it for tuberous Begonia cuttings. I do not recommend its use as a replacement for peat growing composts.
Enjoy your Begonias, they are a challenge but they do bring a lot of pleasure.
Hugh D. McLauchlan