Everyone loves the beauty of begonias, but some gardeners living in the tropics believe begonias come from cooler climates and can’t be grown in the tropics without a lot of effort. But that’s only true of the tuberous rooted begonias that are widely grown in temperate climates during their summer months. Most other types of begonias originate from the tropics or sub-tropics.
Whilst a significant number of begonia species do grow best in the sub-tropics or tropical highlands, there is an equally large number of species that do just as well in the lowland tropics, especially those that are primarily grown for their attractive leaves.
There are nearly 2,000 different species of begonia, and the most distinctive and sought after are tropical species. There’s also a misunderstanding that, like orchids, begonias are difficult to grow. That’s also not true. But just like with orchids, a lot of first timers growing begonias fail because they don’t know the basic rules for growing begonias.
The key to growing begonias is the soil mix. It must be well aerated and well drained, otherwise the roots will rot. The soil mix must be kept damp but never wet for too long or allowed to completely dry out. Whilst different species of begonias may have slightly different cultural requirements, most require bright light but not the direct tropical sun.
That means in the tropics, whilst some species can be grown outdoors under shady trees, most do best in a shadehouse that has 50-80 percent shadecloth. Begonia collectors often construct their shadehouses with a 50 percent section, a 70 percent section, and an 80 percent section so they can move their potted plants around until they have determined just the right level of shade for different species. Most tropical species do best under 70-80 percent shade, unless in the highlands where they will usually tolerate more light.
Regular misting in the shadehouse creates a warm, humid atmosphere – which most begonias love – and some do best in hanging baskets to help the aeration of the roots. The soil mix should not only be well-drained, but it should also be fibrous. In Borneo and Java you can see begonias growing in the wild in pockets of rotting vegetation in limestone rocks or in old leaves in the forks of trees.
Under cultivation, growers have had considerable success with a mix that consists of coarse river sand, peat moss, polystyrene bubbles and a well-rotted mixture of fowl manure and wood shavings.
As already mentioned, watering is critical, and although begonias must be kept damp, they must not be left wet for any length of time. Therefore, during the wet season rains, they must be kept under cover. If growing a collection of begonias in a shadehouse, a sheet of clear polythene should be placed over the shadehouse to avoid the plants from becoming waterlogged.
The main insect pest that affects begonias in the tropics is the cabbage moth, which is easily controlled by spraying or dusting with carbaryl. And if plants are overwatered or left wet for too long, then stem rot will certainly be a problem. Whilst this problem can often be contained with fungicides such as benomyl, it is better to treat the cause rather than the effect. This means repotting the plant into a better drained, more friable potting mixture.
Type of Begonias
Begonias must surely be, next to orchids, one of the most diverse groups of plants in the tropics. There are begonias that look like trees, and some that resemble cacti. But those that gardeners find most appealing are the large, decorative leaved ones.
The main groups of begonias are:
- Rex begonias
- Fibrous rooted begonias
- Cane begonias
- Tuberous rooted begonias
- Rhizomatous begonias
- Novelty begonias
Let’s look at each group in turn and discuss their special needs.
Rex begonias are easily raised from seed, but seldom come true to type. Rex begonias are all hybrids from the original Begonia rex, found in Assam, and without a doubt, the modern hybrids are amongst the most beautifully leaved plants in the world.
To obtain Rex begonia plants that are true to type, propagation can be done from leaf cuttings or rhizome cuttings. In the former case, a mature leaf is either pinned flat onto a suitable propagating medium and cut across the main vein, or small pieces of leaf terminating in a main vein can be used like conventional cuttings.
These leaf pieces, kept moist in a high humidity situation, quickly callus and produce roots and shoots from the cut vein ends. When big enough, the plantlets can be potted up and will be identical to the parent plant.
Fibrous rooted begonias, typified by the many varieties and hybrids of Begonia semperflorens, must rank as the easiest members of the genus to grow. They’re adaptable to a wide range of soils, though like all begonias prefer a sandy, fibrous, well-drained medium.
They will tolerate a wide range of lighting conditions from full shade through to almost full sun in the tropics, one of the few types of begonias that will do that (in cooler climates where the sun is not as strong, they can take full sun all day). They are easily propagated by root division or tip cuttings.
The variety and form of fibrous rooted begonias are diverse. There are green and brown leaved types; single and double flowers; red, pink and white colours, and a wide range of heights and degrees of compactness.
Whilst Begonia semperflorens is best treated as a biennial, or even an annual in some areas, other members of the group such as Begonia fuchsioides can be kept growing indefinitely.
Cane begonias, or ‘angel wings’ as they are often called, can form magnificent specimens two metres or more in height. They develop, as the name suggests, bamboo-like stems and usually have wing-like leaves. These leaves can be plain, blotched, spotted or patterned depending on the variety and species in question.
Flowers are usually crowded together in large, lax panicles and usually highly decorative. Colour is either pink or white in most instances, but dark cherry red and bright orange are notable exceptions.
Propagation of the cane types is usually from tip cuttings, best taken in the wet season. Dry season cuttings are rarely successful as the cooler temperatures at night causes the plant to ‘shut down’ and frequently stem rot sets in before active growth can begin.
Tuberous rooted begonias are not suitable for the high tropics. They prefer a temperate climate and need a winter cold period to induce flowering. I know a few gardeners who have tried to grow tuberous rooted begonias in tropical lowland regions using cold rooms to replicate winter temperatures, but none have succeeded to the best of my knowledge.
Rhizomatous begonias are a fascinating group. Typified by a thick creeping root stock, they produce a wide array of leaf types and varied flower heads. Some have thick waxy leaves and sparsely flowered upright spikes. Others have luxuriant, decorative leaves and massive flower heads.
One species is especially well known as an indoor plant throughout the world. It’s called Begonia masoniana and originates from the tropical forests of northern Vietnam and New Guinea. It’s commonly known as the ‘Iron Cross Begonia’ because of the distinctive pattern on its leaves. This striking rhizomatous begonia is second only in popularity to the rex begonia in tropical shadehouses and is often grown as an indoor pot plant in cooler climates.
Rhizomatous begonias are easy to propagate if the side shoots that emerge from the main stem are taken off during the early wet season. Potted directly into the correct potting mix and kept in a damp, humid situation, growth is rapid and mature sized plants can be attained in one season.
Some rhizomatous begonias can be propagated from leaf cuttings, but like the cane begonias, many will produce roots but no shoots from the leaf cuttings.
Novelty begonias is a label that is applied to begonias that don’t easily fit into the other groups. These include species such as Begonia luxurians and similar palmate plants, and the cacti begonias.
Begonia luxurians, commonly known as the palm leaf begonia, makes a striking landscape plant in shaded areas with its dark red cane-like stems, but it does better in the sub-tropics or tropical highlands than it does in tropical lowland regions. It can grow up to over two metres tall.
With so many different species and varieties available, growing begonias can become a fascinating and sometimes addictive pastime for keen gardeners. Provided the simple rules about growing begonias that we’ve discussed in this article are followed, there is no mystery to growing begonias in the tropics, but a great deal of satisfaction to be achieved and beauty to be enjoyed.
Header image: © Anna Kraynova