Houseplant · Begoniaceae
Rex Begonia
Begonia Rex Cultorum Group
It's all about those painted-looking leaves, and the rex begonia keeps them at their best with bright, indirect light and moving air.
Bright indirect
66–73°F · 19–23°C
USDA 10–11
12–18 in · 30–46 cm
Overview
Here's the thing about the rex begonia: nobody grows it for the flowers. The leaves are the whole reason, swirled with silver, plum, rose, and deep green and often crinkled or curled, while the tiny pink-white blooms are easy to miss. It's part of the Rex Cultorum Group, a big bunch of hybrids that trace back to a wild begonia from the eastern Himalayan foothills.
Instead of a tall stem, it grows from a creeping rhizome, so it stays short and wide, about 12 to 18 inches (30 to 46 cm) tall and roughly the same across. That low, spread-out shape is exactly why a shallow pot on a bright shelf suits it so well.
So is it fussy? A little, yes. The rex begonia is a demanding plant that likes steady warmth, humid air, and a bit of a breeze, and it'll sulk if any of those go missing. Get it right, though, and few houseplants can touch those leaves, but leave it in soggy soil or stale air and it'll go downhill fast.
Care
The short version: bright, indirect light, soil that stays evenly moist in a porous mix that never gets soggy, cozy warmth around 66°F to 73°F (19°C to 23°C), and lots of humidity added through the air around it rather than by wetting the leaves.
Light
Give it bright, indirect light and keep it out of hot, direct sun, which'll scorch those painted leaves. It'll cope in partial to full shade, though the colors go a bit flat there, and a fluorescent light works great if a good window is hard to come by.
Water
Keep the soil evenly moist, letting the top dry out a touch between drinks, and don't let it sit soggy. Water at the soil or from the bottom instead of over the top, since wet leaves are just asking for rot. When winter rolls around and it rests, ease way back.
Soil
Go with a porous, well-drained mix that's rich in organic matter, like a light soilless or African-violet blend. It likes a slightly acidic pH of 5.5 to 6.5, and a shallow pot fits that creeping rhizome way better than a deep one.
Temperature
Steady warmth between 66°F and 73°F (19°C to 23°C) keeps it happy, and it'll slow right down if the nights get much colder. Keep it clear of cold drafts and sudden chills.
Humidity
This plant really wants high humidity, around 50% to 75%, which is more than most homes have in winter. Bump it up with a pebble tray or a spritz of the air nearby, just not the leaves themselves, because wet foliage is the fastest way to fungal trouble.
Feeding
While it's growing from spring into fall, feed it a balanced liquid fertilizer at half strength every couple of weeks, at every other watering. Once fall and winter hit and it takes a break, just stop feeding until spring.
Pruning
There's not much pruning to do here. Just pull off dead or sickly leaves whenever you notice them, which keeps things tidy and lets air move so fungus can't settle in. A pinch at the tips gets it to branch out and fill in.
Repotting
Repot in spring once the roots have packed the pot, moving up to a shallow container that suits the creeping rhizome. When you see roots wrapping around the root ball, that's your sign it's time.
Size & spacing
A grown rex begonia stays nice and compact at 12 to 18 inches (30 to 46 cm) tall and about the same wide. Leave a bit of open space on each side so air can move through and the leaves stay dry.
Troubleshooting
Almost everything that goes wrong with a rex begonia comes down to water and air. Soggy soil and damp, stagnant air bring on the rots and mildews, and a dark spot just washes the color right out of the leaves. Find your symptom below and jump on it early, before it gets worse.
A droopy plant with a dark, mushy base
When soil stays soggy, you get crown and root rot. Once that rhizome goes soft and dark, stop watering and let the mix dry out completely. Repot into fresh, porous soil in a shallow pot, cut off anything that's rotted, and then start watering again slowly and carefully.
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
White powder that will not wipe off the leaves
That white dust is powdery mildew, a fungus that shows up when the air's still and the humidity's high. Pull off the leaves that have it and open up the space so air can move around. And keep water off the leaves from now on, because damp foliage is exactly how it spreads.
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, mushy spots
This one's botrytis, or grey mold, and it turns up on foliage that stays wet in still, muggy air. Snip off the bad parts and toss them in the trash, not the compost. Then water down at the soil instead of over the top, and give the plant a little more room so it can dry out.
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 fluff, fine webs, or speckled new leaves
These are the usual sap-suckers, and each one leaves its own clue. Cottony white bits where the leaves meet the stem? That's mealybugs. Faint webbing and yellow speckling means spider mites, and a little cloud of bugs when you bump the plant is whiteflies. Dab the mealybugs with rubbing alcohol, move the plant away from the others, and keep treating until they're gone.
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
Faded color and stretched-out, leggy stems
If the markings are fading and the stems are stretching toward the window, that's too little light. Move it somewhere brighter with plenty of indirect light, but skip the hot, direct sun. No good window? A fluorescent light fills in nicely.
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
It stops growing and drops leaves in winter
When a rex begonia goes quiet and drops leaves in the cold months, that's usually just winter dormancy from the shorter days and cooler air. The rhizome stays firm even while the leaves fall. Water less, hold off feeding until spring, and get back to normal once new growth shows up.
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
Quick heads-up, because this one matters: the rex begonia is toxic if it's eaten. Every part holds soluble calcium oxalate, and the buried rhizome packs the most. A pet that chews the leaves will drool and get a sick stomach, grazing animals can run into kidney problems, and the sap can leave skin itchy, so it's best kept away from pets, livestock, and little kids.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds · People
Cats Moderate
If a cat chews the leaves, it'll usually drool and throw up as the calcium oxalate irritates its mouth and belly. The buried rhizome has the most of it, so a cat that digs at the base can get hit harder.
Dogs Moderate
A dog that mouths the foliage will likely drool, paw at its face, and feel a bit off. The rhizome's the real problem though, since that's where the toxin's most concentrated.
Horses Severe
Grazing animals get the worst of it. The soluble oxalates can move through the body and stress the kidneys, so a horse that browses on it can end up a lot sicker than a small bite would let on.
Rabbits Toxic
Rabbits nibble low and often, which turns those same kidney-stressing oxalates into a real hazard for them. Keep the plant well out of reach, and don't ever hand them a piece to eat.
Livestock Toxic
Goats, sheep, and cattle face that same whole-body oxalate risk horses do, with a sore mouth and possibly kidney trouble after grazing. Fence it off for good.
Birds Caution
The oxalates that bother mammals make this a poor plant to keep near pet birds too. If a bird's pecking at the leaves, treat it as a problem and keep the curious ones away.
People Caution
None of this plant is meant to be eaten, and the sap can leave some folks with itchy skin or a rash after handling. Wash your hands once you're done pruning, and keep little kids from putting the 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
There are more named rex begonia hybrids than you could ever count, and they're all grown for the leaves. Here's one the botanical record calls out by name.
Begonia rex-cultorum 'Super Curl'
It's one named pick from the heavily hybridized Rex Cultorum Group, grown just like the others for its bold, patterned leaves rather than any flowers.
How to propagate
Want more of them? Rex begonias make that surprisingly easy, and a single leaf can turn into a whole bunch of new plants. Spring and summer are the time to go for it, while the plant's actively growing.
Leaf cuttingsModerate
Spring to summer · Plantlets form in 1-3 months
Leaf cuttings are a fun one to try in spring or summer while the plant's growing. Cut across the big veins on the underside and lay the whole leaf flat on damp media, or slice it into wedges that each keep a main vein. New little plantlets pop up from those cuts over the next one to three months.
DivisionEasy
At repotting in spring · Several weeks
The easiest way is to just split the plant while you're repotting it in spring. Pull the rhizome into pieces, making sure each one has its own roots and leaves, and pot them up on their own. They'll settle in within a few weeks.
Stem cuttingsModerate
Spring to summer · Several weeks
Stem cuttings work too, taken during the spring and summer growing season. Stick a cutting in moist media and it'll root within a few weeks.
Myths
Rex begonias are mostly about the flowers.
Not really, no. The leaves are the main event, twisting color and texture together in a way most plants can't, while the flowers stay small, pinkish-white, and pretty forgettable. The whole point of a rex begonia is the foliage.
A begonia's calcium oxalate is the same harmless mouth-irritant you find in aroids.
They're actually pretty different. Aroids have insoluble oxalate crystals that sting the mouth and then pass, but the ASPCA says the begonia's toxin is soluble calcium oxalate, which the body can absorb. For grazing animals, that difference can mean kidney failure instead of just a sore mouth.
Misting the leaves is the best way to give a rex begonia its humidity.
Sounds right, but it backfires. Rex begonias do love humid air, and yet wet leaves invite the exact fungi that plague them, powdery mildew and botrytis especially. Raise the humidity in the air around the plant instead, with a pebble tray or a spritz of the nearby space. Keep the leaves themselves 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