How to Grow Rex Begonias

rex begonias on an outdoor deck

The Spruce / Kara Riley

The name "rex begonia" is applied to a group of cultivated begonia hybrids that have the wild Begonia rex species as one of the genetic parents. These tropical plants have been bred to have unusual markings, leaf shapes, and colors. Many are variegated in shades of green, red, pink, purple, silver, and brown. The leaves grow on short leaf stalks emerging from underground rhizomes. The leaf edges and undersides are covered with short red hairs.

The flowers are usually pink, though they are small and incidental. Most growers recommend that you cut off the flower stalks to direct the plant's energy to the spectacular leaves.

Although they are at home in a shady garden, rex begonias are also popular as houseplants. Many people collect and display several varieties. When grown in the garden, they are normally planted in spring from potted nursery starts, or occasionally from rhizomes packaged in peat moss or sawdust. When planted from rhizomes, they will reach flowering maturity in 12 to 14 weeks.

Botanical Name  Begonia rex-cultorum
Common Name  Rex begonias
Plant Type  Herbaceous perennial, usually grown as a houseplant
Mature Size  12–18 inches tall and wide
Sun Exposure Part shade to full shade; bright filtered light when grown indoors
Soil Type Light rich soil; standard potting mix when grown as houseplants
Soil pH 5.7–6.2  (acidic)
Bloom Time Summer
Flower Color Varies; usually pink
Hardiness Zones 10–12 (USDA); usually grown as houseplants
Native Area  Northeastern India, southern China, and Vietnam
Toxicity Mildly toxic to humans and animals
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Watch Now: How to Grow and Care for Rex Begonias

closeup of begonias
​The Spruce / Kara Riley 
overhead view of begonias
​The Spruce / Kara Riley 
rex begonias grouped together
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Rex Begonia Care

Rex begonias can be very demanding when grown in the garden, thriving only if you give them just the right amount of water, food, and humidity. Varieties differ in their needs, and the only way to know what your plant wants is to watch it, once it has adjusted to its new surrounding. If it's flourishing, continue with what you were doing. If it is droopy or gangly, adjust the light and water. Eventually, you'll figure out the right balance.

Be sure your garden beds or containers meet the requirements of the rex begonia. Alternatively, if your area is too cold, consider growing yours as a houseplant or in an outdoor container that can be brought indoors in cooler weather.

To really play up the unique qualities of begonia rex, pair them with solid green plants with different textures or forms. They look great outdoors in shady tropical gardens, but the most popular way to display rex begonias is to collect and group them together, each in its own pot.

Light

These plants will grow best in part shade to full shade. They need some light to keep their coloring, but bright, indirect light is best. When grown as an indoor plant, give them a location with plenty of bright indirect light.

Soil

Rex begonias prefer light, rich soil. When planting directly in the ground, a moist, well-drained location is optimal and mulch will keep the roots shaded. In pots, be sure to provide drainage holes. A peat-based potting mix is ideal for growing in containers.

Water

Begonia rex should be watered when the soil or pot feels dry, but don’t wait until the plant starts to wilt. You can cut back on water during their dormant period in the winter, watering only when the pot dries out. Humidity is crucial to keeping your rex begonia happy; however, spraying the leaves can lead to spotting. It’s better to cluster your plants, so they can create their own humid environment, or use a pebble tray filled with water to provide steady humidity.

Temperature and Humidity

Begonia rex is sensitive to temperature changes and to temperatures below about 60 degrees Fahrenheit. You can keep them happy as houseplants or store them dormant over winter, as you would with other tender bulbs. These plants do require high humidity (more than 50 percent), which means it can be difficult to maintain growing rex begonias indoors over the winter.

Fertilizer

You can feed your potted plants monthly with any good houseplant food. Too much food will make for a scraggly plant, so pay attention and adjust the feeding to suit your variety. Rex begonias can be temperamental and you just have to find the right conditions and balance for your plant. Don’t feed at all during the winter.

Are Rex Begonias Toxic?

Rex begonias are among the many plants whose leaves contain calcium oxalate crystals. When eaten, these crystals can irritate the mouth and throat. Poison control agencies, however, generally do not list rex begonia as a plant that is toxic to humans. Consumption of large quantities potentially can be a different matter, but this is quite rare since the effect of chewing the bitter leaves is immediately unpleasant. Grazing animals, especially horses, have been known to experience serious poisoning, including kidney damage.

Symptoms of Poisoning

A person or pet that eats leaves of a rex begonia may experience irritation to the mouth and throat, excessive drooling, nausea, and vomiting. Rarely, severe throat irritation can cause swelling and breathing problems.

Serious illness is very rare, except possibly for grazing animals who eat large quantities. The medical treatment for a child who accidentally eats a leaf may be simply to drink cold water. A veterinarian usually simply suggests that a pet be given a liquid diet for a couple of days.

Rex Begonia Varieties

There are many beautiful hybrid varieties available, but they are often unlabeled or mislabeled. Make sure to ask questions so you know exactly what you're buying. Some popular varieties include:

  • Begonia rex 'Boston Cherries & Chocolate': Red and silver spots appear on dark leaves.
  • Begonia rex 'Escargot': Spiraling markings and the way the leaves circle inward make each leaf look like a snail.
  • Begonia rex 'Fireworks': Wing-shaped silver leaves are etched with purple.
  • Begonia rex 'Snow Queen': This variety has silvery leaves and is known to have good disease resistance.

Pruning

Dead or diseased leaves should be trimmed off down to the main stem or soil level. Rex begonias can sometimes develop scraggly bare spots as the stems grow old and woody. When this happens, simply clip off the stems to just above soil level. Very shortly, new stems with fresh new leaves will sprout.

Propagating Rex Begonias

Though growing rex begonias from seeds is theoretically possible, they are so tiny and take so long to mature into rhizomes that it is rarely done. Instead, rex begonias are more easily propagated by clipping a single leaf with an attached section of stem, and placing it in water until roots begin to grow. When a good network of roots has developed, plant the cutting in potting soil. Leave the existing leaf in place until small new leaves begin to sprout, then cut it off. The new plant will become a full-sized adult within a couple of months.

Cuttings can also be rooted by planting them directly in a mixture of moist peat moss and perlite. Keep the cutting moist until new leaves begin to sprout, then cut off the original leaf and transplant the specimen into a pot with fresh potting soil.

Potting and Repotting Rex Begonias

Repotting rex begonias each spring will ensure that they have plenty of soil to grow in, but they like to be a little bit pot bound. Large or gangly plants can be pruned into shape. Rotating potted rex begonias will keep the plants full and stocky.

3 types of begonias
​The Spruce / Kara Riley

Common Pests/Diseases

Bacterial leaf spot, mildew, and botrytis can occur if the leaves stay wet. Root rot can be a problem in wet areas. To avoid these issues, be sure your begonias are in well-drained soil and water them sparingly. If you live in an area that's prone to flooding, growing your begonias in a pot will give you the option of bringing them under shelter in rain.

Mealybugs, aphids, and caterpillars can also become problems. In most cases, a spray form of pesticide will take care of the issue. Handle slugs and snails by placing slug bait near your plants.