Houseplant · Begoniaceae
Rex Begonia
Begonia Rex Cultorum Group
Grown for leaves that look painted, the rex begonia rewards bright, indirect light and air that keeps moving.
Bright indirect
66–73°F · 19–23°C
USDA 10–11
12–18 in · 30–46 cm
Overview
The rex begonia is a houseplant you keep for its leaves. Each one is a swirl of silver, plum, rose, and deep green, often spiraled or puckered, and the small pink-white flowers barely register next to them. It belongs to the Rex Cultorum Group, a sprawling line of hybrids bred from a wild species native to the foothills of the eastern Himalayas.
It grows from a creeping rhizome rather than a single upright stem, staying compact at 12 to 18 inches (30 to 46 cm) tall and about as wide. That low, spreading habit suits a shallow pot and a spot on a bright shelf or table indoors.
None of this comes free. The rex begonia is a demanding plant that wants steady warmth, high humidity, and air that keeps moving, and it sulks when any of those slip. Get the balance right and the foliage is hard to match, but it punishes overwatering and stale air faster than most houseplants.
Care
The short version: bright, indirect light, evenly moist soil in a porous mix that never gets soggy, warmth around 66°F to 73°F (19°C to 23°C), and high humidity raised through the air rather than by wetting the leaves.
Light
Give it bright, indirect light and keep it out of hot, direct sun, which scorches the patterned leaves. It will get by in partial to full shade, though the color fades there, and a fluorescent fixture fills in nicely where a window falls short.
Water
Keep the soil evenly moist but let the surface dry a little between waterings, and never let it sit soggy. Water at the soil or from below rather than over the top, since wet leaves invite rot. Ease off through the winter rest.
Soil
Plant it in a porous, well-drained mix rich in organic matter, like a light soilless or African-violet blend. A slightly acidic pH of 5.5 to 6.5 suits it, and a shallow pot matches the spreading rhizome better than a deep one.
Temperature
Steady warmth between 66°F and 73°F (19°C to 23°C) keeps it happy, and growth slows when nights dip much below that. Shield it from cold drafts and sudden chills.
Humidity
This plant wants high humidity, around 50% to 75%, more than most homes offer in winter. Raise it with a pebble tray or by spraying the air nearby, never the leaves themselves, since damp foliage is the fastest path to fungal disease.
Feeding
During the spring-to-fall growing stretch, feed with a balanced liquid fertilizer at half strength, given every couple of weeks at alternate waterings. Stop feeding through fall and winter while the plant rests.
Pruning
It needs little pruning. Pull off dead or diseased leaves as soon as you spot them, both to tidy the plant and to keep air moving and fungus at bay. A pinch at the growing tips encourages it to branch and fill out.
Repotting
Repot in spring when the roots have filled the pot, moving up to a shallow container that fits the creeping rhizome. Circling roots wrapping the root ball are your cue that it's time.
Size & spacing
A mature rex begonia stays compact, reaching 12 to 18 inches (30 to 46 cm) tall and spreading about the same. Give it a little open space on each side so air can circulate and the leaves stay dry.
Troubleshooting
Most rex begonia trouble traces back to water and air. Soggy soil and damp, still air bring on the rots and mildews, while a dim corner drains the color from the leaves. Match what you see below and act early, before a small problem spreads.
A wilting plant with a blackened, mushy base
This is crown and root rot, and it comes from soil that stays soggy. Once the rhizome turns soft and dark, stop watering and let the mix dry out. Repot into fresh, porous media in a shallow pot, trim away anything rotted, and ease back into watering.
Fix:
- Stop watering and allow the mix to dry
- Repot into fresh porous, well-draining mix and a shallow pot, trimming away rotted tissue
- Resume careful watering, avoiding waterlogged soil
Dusty white patches that won't rub off the leaves
This is powdery mildew, a fungus that takes hold when the air sits still and humidity runs high. Pull off the marked leaves and open up the space around the plant so air can move. Keep water off the foliage, since wet leaves are what let it spread.
Fix:
- Remove and discard affected leaves
- Improve air circulation around the plant
- Avoid wetting foliage; spray the surrounding air rather than the leaves to raise humidity
Fuzzy grey mold on soft, collapsing tissue
Botrytis, or grey mold, settles on leaves that stay damp in still, humid air. Cut away the affected parts and destroy them rather than composting. Water at the soil instead of over the top, and give the plant more room to breathe.
Fix:
- Remove and destroy affected plant parts
- Increase air circulation and lower ambient moisture on foliage
- Stop misting/wetting leaves; water at the soil
Cottony clusters, fine webbing, or stippled new leaves
These are the usual sap-feeding pests, and the clues differ. Cottony white tufts in the leaf joints mean mealybugs, fine webbing with yellow speckling points to spider mites, and a cloud of tiny insects when you brush the plant signals whiteflies. Dab mealybugs with rubbing alcohol, isolate the plant, and keep treating until they clear.
Fix:
- Dab mealybugs with rubbing alcohol on a cotton swab
- Isolate the plant to prevent spread
- Treat repeatedly until pests are gone, raising humidity to discourage spider mites
Washed-out color and stretched, leggy growth
When a rex begonia sits too dim, the leaves lose their markings and the stems reach toward the window. This is too little light, and the fix is a brighter spot with plenty of indirect light, never hot direct sun. A fluorescent fixture works well where a window can't.
Fix:
- Move to a brighter spot with plenty of bright, indirect light (avoid direct, hot sun)
- Supplement with fluorescent lighting if natural light is limited
Growth stalls and leaves drop as winter sets in
A rex begonia going quiet in the colder months is usually just winter dormancy, brought on by shorter days and cooler air. The rhizome stays firm even as the leaves fall. Cut back on water, hold off feeding until spring, and pick up normal care once new growth appears.
Fix:
- Reduce watering and keep the soil barely moist
- Stop fertilizing until new spring growth appears
- Resume normal care when active growth resumes in spring
Toxicity
Handle this one with care, because the rex begonia is toxic. Every part holds insoluble calcium oxalate, and the buried rhizome holds the most. Chewing the leaves leaves cats, dogs, and other animals drooling and sick, grazing animals can suffer kidney effects, and the sap can irritate skin, so keep it away from pets, livestock, and small children.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds · People
Cats Moderate
A cat that chews the leaves will usually drool and vomit as the calcium oxalate irritates the mouth and gut. The buried rhizome holds the most, so a cat that digs at the base can get a worse dose.
Dogs Moderate
Expect drooling, mouth pawing, and an upset stomach after a dog mouths the foliage. Eating the rhizome is the real danger, since that is where the toxin sits thickest.
Horses Severe
Grazing animals fare worst here. The oxalates can move through the body and strain the kidneys, so a horse that browses the plant can end up far sicker than a quick nibble would suggest.
Rabbits Toxic
Rabbits graze low and steadily, which makes the same kidney-stressing oxalates a genuine hazard. Keep the plant well out of reach and never offer any part as food.
Livestock Toxic
Goats, sheep, and cattle face the same systemic oxalate risk as horses, with mouth irritation followed by possible kidney trouble after grazing. Fence it off entirely.
Birds Caution
The oxalates that trouble mammals make this a poor choice around pet birds too. Treat any pecking at the leaves as a problem and keep curious birds away.
People Caution
No part of the plant is meant to be eaten, and the sap can leave some people with itchy skin or a rash when they handle it. Wash up after pruning and keep small children from putting leaves in their mouths.
NC State and UConn note the sap contains calcium oxalate and can cause skin irritation/contact dermatitis in some people when handling
Helpline numbers
United States
ASPCA Animal Poison Control: (888) 426-4435 (fee applies)
Poison Control: (800) 222-1222
Canada
Poison Centres: 1-844-764-7669
Varieties
Rex begonias come in countless named hybrids, all grown for their foliage. One worth knowing by name is documented in the botanical record.
Begonia rex-cultorum 'Super Curl'
A named cultivar in the widely hybridized Rex Cultorum Group, grown like the rest of the line for its showy, patterned foliage rather than its flowers.
How to propagate
Rex begonias are generous about making more of themselves, and a single leaf can turn into a tray of new plants. Spring and summer are the time to try it, while the plant is in active growth.
Leaf cuttingsModerate
Spring to summer · Plantlets form in 1-3 months
Take leaf cuttings in spring or summer when the plant is growing. Cut across the major veins on the underside and lay the whole leaf flat on moist media, or slice it into wedges that each hold a main vein. New plantlets push up from the cut veins over the next one to three months.
DivisionEasy
At repotting in spring · Several weeks
The easiest route is to split the plant while you repot it in spring. Pull the rhizome apart into pieces, making sure each piece carries its own roots and leaves, and pot them up separately. They settle in within a few weeks.
Stem cuttingsModerate
Spring to summer · Several weeks
Rex begonias also grow from stem cuttings taken during the spring and summer growing season. Root a cutting in moist media and it takes hold within a few weeks.
Myths
Rex begonias are grown mainly for their flowers.
These plants earn their place with leaves, not blooms. The foliage comes in swirls of color and texture that carry the whole show, while the flowers stay small, pinkish-white, and easy to miss. You grow a rex begonia for what's underfoot, not overhead.
A begonia's calcium oxalate is the same harmless mouth-irritant found in aroids.
The two are not alike. Aroids carry insoluble oxalate crystals that sting the mouth and pass, but the ASPCA flags the begonia toxin as soluble calcium oxalate, which the body can absorb. In grazing animals that difference can mean kidney failure rather than a sore mouth.
Misting the leaves is the best way to give a rex begonia the humidity it wants.
Rex begonias do crave humid air, but wet leaves invite the very fungi that plague them, powdery mildew and botrytis chief among them. Raise the moisture in the air around the plant instead, with a pebble tray or by spraying the surrounding space. Keep the foliage itself dry.
Sources
- ASPCA Animal Poison Control
- NC State Extension Gardener Plant Toolbox
- Clemson Cooperative Extension HGIC
- Missouri Botanical Garden Plant Finder
- University of Connecticut Home & Garden Education Center
- Pet Poison Helpline
- University of Illinois Extension
- Plants of the World Online, Royal Botanic Gardens Kew