Rex begonia, or Begonia rex-cultorum, is a cultivar group of the begonia plant species that produces attractive and abundant foliage with the proper care. This plant is a rhizomatous perennial with striking leaves that grow in vivid colors, shapes, and patterns. In this guide, I’m going to share how I care for my Rex begonia at home, including the best soil types, watering frequencies, fertilizing needs, light exposures, and ideal environmental conditions for optimal growth.
What to Do Before Planting
Here are a few steps to take before bringing your new Rex begonia home.
- Have a wide, shallow potting vessel and saucer ready to repot your new plant.
- Make sure you have the suitable soil and tools available before repotting your rex begonia. These items are detailed below.
- Find a lovely space in your home to place your rex begonia. It will thrive in an area with plenty of indirect sunlight.
In my experience, Rex begonias typically reach a maximum height of around 1.5 feet. Their shrub-like quality means they will reach a similar maximum spread of around 1.5 feet. Expect plant growth to accelerate in the warm spring and summer months.
How to Plant
I find the most suitable pots and planters for rex begonias are wide and shallow to make room for their growing rhizomes. Rex begonias prefers a well-draining pot, so clay pots with drainage holes work well. These plants also grow well in a hanging basket.
The ideal pot size for your rex begonia will depend on its current size. Since the rhizomes need room to grow, it is best to ensure the plant has an inch or so of space around the root ball to grow outward. Repotting yearly to make extra room for the rhizomes will keep your rex begonia growing happily.
Best Soil Mix
My Rex begonia thrives best in a light, balanced potting mix. These plants love well-draining soil that retains some moisture, so adding elements like peat and a layer of stones at the bottom of the container will ensure the plant has everything it needs to thrive. Rex begonias also enjoy loam, sandy, and chalky environments.
In my experience, Rex begonias grow most vigorously in an area with ample bright, indirect sunlight. I locate my plant near an east-facing window, which receives soft morning sunlight and bright, indirect light through the rest of the day.
I also find that it’s beneficial to turn the plant regularly to ensure it receives even light across all of its foliage. I’d recommend a quarter turn each week to help your rex begonia maintain even growth.
Temperature and Humidity
My Rex begonias tend to be picky when it comes to temperature and humidity. As begonias are tropical and subtropical plants, they enjoy a mild, moist environment. Their ideal temperature for your rex begonia is between 60 and 70 degrees Fahrenheit.
Despite this plant’s tropical roots, it is essential to strike a balance regarding moisture. The rex begonia thrives in humidity above 50 percent, but it is sensitive to overwatering and can develop mildew with excess moisture.
I find that bathrooms and kitchens are often good locations in the home if you’re growing indoors, though a warm spot near a south or east-facing window is also an excellent option.
As a general rule, I allow my rex begonia’s soil to drain and dry to between 50 – 75% in between waterings to avoid excess moisture. A soil probe or moisture meter can help to ascertain the precise moisture level, though it is not essential (a simple touch of the soil with your fingers will also give you a good reading).
The plant may also wilt slightly, which is a good indicator that it is time to water it again. This should occur approximately every 7 to 10 days in spring and summer and around 14 to 21 days during the late fall and winter months.
I water my rex begonia at the base to avoid wet leaves and overwatering.
Myr Rex begonia enjoys a balanced fertilizer (meaning an even amount of nitrogen, phosphorus, and potassium – usually referred to as the “NPK” ratio) during its growth period in the warmer months. Y
I feed mine with a complete formula at a quarter strength every 3 to 4 weeks during the summer. Minimize your fertilization schedule as fall approaches, and stop fertilizing the plant during its dormant winter months.
Usually, the king begonia does not require any pruning. If you find that the plant’s rhizomes outgrow the container without producing more foliage, you can trim them back. You can also use these cuttings you take from the rhizome to grow new rex begonia plants.
Since the rex begonia only lives a few years, a great way to get more longevity from the plant is to propagate it. I follow these steps to propagate new rex begonias from my original plant.
- Gather the supplies you need to propagate your plant: water, scissors, shears, small pots for cuttings and new plants, soil, plastic film, and small stones.
- Take cuttings from a healthy leaf or overgrown rhizome on your plant. You can use a full, healthy leaf by cutting away the stem and making half-inch cuts across the biggest veins in the leaf.
- Place the leaf underside down in the soil using pins, but avoid piercing the veins. The cuts you made are where new plants will grow, so these areas must touch the soil. You can use stones to keep the leaf flat against the soil.
- Cover the pot with plastic film to maximize the humidity and light it receives. Keep the soil moist while your new plants take root.
- Wait up to six weeks for the new plants to grow. You can place them into their new pots once they are around three inches in height.
I find that I need to repot my Rex begonia every 12 to 18 months to make room for its rhizomes. They spread outward, so I focus on increasing the width of the plant’s pot so that it has enough soil to spread and grow.
Common Problems and How to Treat Them
In my experience, a lot of common issues that crop up with Rex Begonia plants are related to water and moisture. It is essential to find the right balance, not only to help the plant thrive but to avoid frustrating issues like those mentioned below.
Common Pests and Diseases
Here are a few of the common pests and diseases to know about when it comes to caring for your king begonia plant.
- Powdery mildew
- Bacterial leaf spot
- Botrytis fungal infection
I find that powdery mildew is an especially pesky problem with these plants which can travel to affect other plants in your home. Ensure the affected plant is isolated from other begonias, preferably in an area with good air circulation. I treat the mildew with a fungicide or homemade spray, using a mixture of water, dish soap, and baking soda, until it subsides.
Essential Tools to Have Around
Now, it’s also great to keep the right tools available for optimal care of your rex begonia. Here’s a list of the tools and materials I use for optimal begonia rex plant care at home:
- A wide, shallow, well-draining container and saucer or hanging basket
- Well-draining soil
- A balanced fertilizer
- Plastic film for propagation
- Small pots for cuttings and new plants
- Small stones for propagation or added drainage in the plant’s container
About Rex Begonia Plants
The rex begonia, or begonia rex, descends from the B. rex variety native to zones in eastern Asia. Through the years, gardeners have crossed the species with other rhizomatous begonia varieties, contributing to the nearly 2,000 species of begonia that exist today.
Charles Plumier, a French botanist, coined the word begonia. He named the species after Michel Bégon, a French official and avid lover of botany who lived from 1638 to 1710. The word rex has Latin roots stemming from the word regere, and means ‘a king.’ This may be why the rex begonia earned its nickname, king begonia.
Where Are Rex Begonia Plants Native?
The rex begonia is native to parts of India, China, and Vietnam, particularly in tropical and subtropical climates. It grows naturally in forests and rocky landscapes. Today, many plant lovers grow the rex begonia as a houseplant all over the world.
Common Rex Begonia Varieties to Grow as Houseplants
Its showy leaves make the rex begonia a common houseplant, though its requirements mean it is challenging for some new houseplant owners. The trick is finding a balance for watering the plant, ensuring it isn’t over or under-watered.
With that said, rhizomatous begonias grow better as houseplants than tuberous varieties since these are more particular about light and humidity levels. A few other common begonia varieties to grow as indoor plants include the following:
- Begonia maculata
- Begonia masoniana
- Begonia erythrophylla
- Begonia acetosa
- Begonia bowerae
- Begonia Cleopatra
- Begonia aconitifolia
- Cracklin rosie begonia
Rex Begonia Toxicity and Pet Friendliness
The American Society for the Prevention of Cruelty to Animals (ASPCA) lists the rex begonia as toxic to cats, dogs, and grazing animals like horses. This is because of the soluble calcium oxalates in this plant, which can cause kidney failure in grazing animals and vomiting or salivation in cats and dogs upon consumption.
Rex Begonia Plant FAQs:
Can rex begonias be grown indoors and outdoors?
Yes, rex begonias can grow indoors and outdoors, though they are more common as indoor houseplants.
How long do rex begonias live?
Like most begonias, your rex begonia will likely live around two to three years. Propagation is a good way to get more plants from your original rex begonia.
The rex begonia cultivar is a dramatic and vibrant plant to incorporate into your houseplant collection. It is a beautiful rhizomatous variety, well worth the effort it takes to care for and grow. With the right attention and maintenance, this regal king begonia will thrive in any space, showing off its deep burgundy, silver, and green foliage for years to come.
Further reading: Discover an amazing collection of purple houseplants you can grow at home.
Andrew is the Editorial Director at Petal Republic. He holds a BSc degree in Plant Sciences and has trained professionally at leading floristry schools in London and Paris. In amongst overseeing a global editorial team, Andrew's a passionate content creator around all things flowers, floral design, gardening, and houseplants.