Last Updated on September 29, 2021 by Grow with Bovees
Rex begonia — ‘the showboat of the begonia world’ according to The American Begonia Society.
If, like me, you have had mixed success with Rex Begonias, you will be pleased to know that there are practical solutions to the problems so many of us have encountered.
When I think how many times I have returned home with a beautiful healthy plant and showered it with love, only for it to die within weeks.
If I’d only had more experience or access to the internet, I believe the story would be very different.
It’s definitely well worth putting the effort into learning the basic rules of caring for Begonias, whether you want to know about Rex begonia care indoors or outdoors.
Begonia Rex or, the Begonia Rex cultorum group as they are often referred to, is a semi-tropical, perennial plant, reaching anywhere between 12 and 24 inches in height, so they can be grown as both indoor plants or outdoors in the garden.
Alternative names for Rex Begonia include; Painted Leaf Begonia and King Begonia but shouldn’t be confused with other species such as Iron Cross Begonia.
There are hundreds of hybrids with their wide range of striking colors, varying leaf shapes and bloom colors and sizes.
Some begonia species are particularly attractive even when not in bloom, like the Salsa Begonia whose leaves have a red center graduating out to pale green finishing with a dark green rim.
Do Rex Begonias Like Sun, Shade (or Bright Indirect Light)?
Well, the easy answer is, both.
Rex Begonia or Begonia rex-cultorum, to give it its full title, thrives in the shade, but at the same time needs a lot of indirect light to produce a fuller plant with trademark pink flowers.
It is best to avoid direct sunlight, otherwise there is a danger the leaves begin to go brown, so if you can find a spot under dappled sunlight, or in a north or east facing window with bright, indirect light year-round, that would be ideal.
If you live in a mild moist climate, you may be able to grow your Rex Begonia outdoors, as they do in their native habitat.
We all have that one shady spot in the garden where sun-loving plants simply will not grow; a warm spot that is crying out for a beautiful plant with bright colors, and Begonias thrive as a bedding plant.
Begonias are cultivated for their beautiful brightly colored leaves, rather than its flowers. As a result they do not require as much sunlight as a plant cultivated for its flowers.
People in less sympathetic climates keep their Begonia’s indoors, where they enjoy a north or east facing aspect.
It is important that your plants have adequate light, whether that is reflected light, dappled light or even fluorescent light.
In fact, your Begonia thrives under artificial light/fluorescent lights, or indoor growing lights.
It is a good idea to move your plant around until you find a spot that suits it best.
Begonia Rex flourishes in similar conditions to plants like orchids and African violets, so the only thing to be careful of indoors is the tendency to dry air due to central heating.
Preparation and Maintenance of the Soil
It is important to ensure that the soil is suitable. Clay soil will simply not work for your Begonia.
You will need to prepare your hole well, ensuring a good mix of porous potting soil or specially prepared fast-draining composted soil with a mix of peat to improve drainage.
How Often Should You Water Begonia rex?
How often to water your plant depends on several things, including the season, day and nighttime temperature and humidity.
It is important to keep both your soil moist and your plant moist, but it is equally important to avoid soggy soil.
You will be aiming for a humid environment but not for overly wet conditions.
The ideal daytime temperature is around 70 °F, with a mean moderate temperature between 60–70 °F.
The nighttime temperature should not dip below 60 °F.
In the winter months, some types of begonias go dormant, and then it is best to water them only once a month.
In the summer months you should water them twice a week, and occasionally they will also appreciate a dose of plant feed.
Begonias do not like to be over-watered, so it is best to test your soil before watering.
A simple fingertip test is the most reliable method. Dig your finger into the soil. If the top inch of soil is moist, delay watering.
Your begonia plant will prefer well drained soil and should never be over-watered. Avoid getting water onto the leaves when watering. Wet leaves are likely to develop fungal diseases.
It is recommended that you feel the humidity levels in the soil before watering, or use a soil moisture tester which will remove the element of chance.
Over-watered plants will develop powdery mildew or leaf rot which are difficult to get rid of.
Should I Mist My Rex Begonia?
When it comes to humidity, rex Begonias will enjoy regular misting if you live in a dry climate. However, do not overdo the mist.
Droplets should not form on the leaves when misting, and you should always use distilled water.
If you’re growing rex begonias indoors then try to find your plant a spot with plenty of indirect light and soil which is well drained and not too moist.
Begonias do not respond well to over-watering, so check how deep the moisture of your soil is before watering.
Rex Begonia Propagation
Rex Begonia has a limited lifespan even in ideal conditions. Most plants live at most for about two to three years, which is also why they only get to a maximum of 24 inches tall.
However, it is not always necessary to buy a replacement, because propagation of begonias is both easy and rewarding.
Rex Begonia is a hybrid, one of several hybrid rhizomatous begonias.
Unfortunately, rhizomatous plants cannot be propagated from seeds.
However, because a rhizomatous plant has rhizomatous roots, it can be propagated by dividing and re-potting the divided rhizome, to form new plants.
Re-potting of your Begonia Rex plant should take place within the active growing season, not during the dormant period.
The rhizome is the fat tuberous root which is easily parted to enable you to repot the separated sections.
Separate the rhizomes carefully, ensuring that each piece has both root and leaf growth before potting them.
Your Rex Begonia plant can even be propagated by removing a small branch of the plant or by taking a leaf cutting from a single healthy leaf.
Leaf cuttings can be dipped into rooting compound before being placed in a peat based potting mix.
Alternatively, you can lay the leaf on top of the potting mix with small cuts on the underside of the leaf vein and secure it in place with a couple of pieces of bent garden wire.
It will then develop roots, and become a new plant, which will be identical to the old one.
Rex Begonia Care Outdoors
Although Rex Begonia is primarily a houseplant, if you live in a warm, humid climate, you may be able to grow your Begonia Rex outdoors.
Most varieties of Rex begonia thrive best in grottoes and near streams and water courses, but any spot with moist air, well drained moist soil and filtered sunlight will be suitable.
With their interesting shapes and bright leaf colors, they make a beautiful show of attractive, eye-catching plants.
One thing to bear in mind, though, is that they tend to be annual plants when planted in the ground.
Are Rex Begonias Prone to Diseases & Pests?
Being a relatively dense plant, begonias are prone to a few pests and common plant problems.
The biggest plant disease, specific to Begonias is powdery mildew, a fungal infection.
It can be identified by a gray or white powdery substance which appears on infected leaves, stems and flowers, and generally on younger plants.
Start by removing the infected leaves and dispose of them immediately before it spreads to the entire plant.
Bacterial leaf spot or Botrytis fungal infection is caused by the plants being too moist or by non-porous soil. Ensure that your soil is well drained, and porous.
Adding peat moss to your soil mixture will help with drainage, and whatever you do, do not overwater!
When watering, ensure that the soil is starting to dry out before adding more water, and never water over the leaves. Empty out the drip tray once your plant is watered.
It is advisable to isolate the infected plants because the infection spreads easily to other plants, particularly to young plants.
The biggest plant pest problem tends to be mealybugs.
You can keep mealybugs at bay by keeping your plant neat and tidy; removing any dead, wilted or withered leaves, and ensuring that the plant has good indirect light.
If you have already been affected by mealy bugs, a paste of garlic, onion and paprika can be made up.
Add a cup of water, strain the mixture and then add a tablespoon of dish soap. Mix well and spray directly onto the plants. Repeat daily for a week.
Good companion plants for begonias include; impatiens, coleus and Brigadoon St. John’s Wort.
Finally, begonias are also prone to root rot, which again is caused by over-watering.
If your plant seems to have stunted growth or is drooping and wilted, pull it out of the soil and check its roots. You should be able to identify the problem immediately.
Carefully cut away the rotted portion of the roots, and re-pot in better soil.
Rex Begonia Crispy Leaves
Just as Begonia’s do not do well if overwatered, it is also important to ensure that your plant does not dry out and die of thirst.
If your plant is turning brown, with brittle leaves/dead leaves, it is likely to be one of three causes.
The first is insufficient water. If you find that your plant has dried out completely, place the plant, in its pot, in a basin of water, about two inches deep. Allow the plant to sit in the water for about thirty to forty-five minutes before removing it.
Allow it to drain for a few minutes before putting it back on its shelf.
The second reason might be that the spot your Begonia is sitting in is too hot.
Begonias like a temperature range of between 60-70 °F. Temperatures above 70 °F will cause your leaves to turn brown and crisp.
Finally, your plant may be in a spot where it gets direct sunlight. Rex Begonia prefers shady spots with indirect light.
How Many Rex Begonia Plants Can I Put In One Pot?
A single begonia requires enough space to spread.
A six-inch pot is sufficient for a single plant, but if you want more plants in a pot, a twelve-inch pot will take between two and four plants. You need to leave plenty of space between them for air circulation.
If the pot starts to look too full, you can easily repot your begonias into a larger pot, or separate them into smaller pots.
Rex begonias respond well to being transplanted, and generally have a growth spurt after being repotted.
How Long Do Rex Begonias Live?
The average lifespan of a begonia is two to three years, so do not feel you have failed your plant if it does not live longer than that.
The good thing is that your Begonia plant will respond well to being separated and repotted. With each new plant in fresh well aerated soil, you will have four or five newly propagated specimens in place of the one that you lost.
It is also a good idea to remove the flower stalks as soon as the blooms have died off, so that more of the energy is directed to producing more beautiful leaves.
If you are buying your plant for the outdoors, remember that it definitely prefers shady spots and temperate weather.
Indoors, they are the happiest out of direct sunlight, but not in complete shade, so bright indirect light is the ideal environment, a good spot would be close to your Angel wing begonia!
One note of caution; Rex begonia plants contain soluble calcium oxalate which is poisonous to cats and dogs.