How to Grow Rex Begonias: Care, Propagation, Troubleshooting

Rex begonias thrive in bright indirect light, high humidity around 50% or more, temperatures between 60°F and 80°F, a fast-draining potting mix, and careful watering that lets the top inch of soil dry out before you water again. Get those five things right and you'll have some of the most dramatic, colorful foliage in your home. Get them wrong and you'll deal with root rot, faded leaves, and powdery mildew before you know it. This guide walks you through exactly what to do, from choosing a pot to propagating new plants.

What makes rex begonias different from other begonias

Rex begonias (Begonia rex-cultorum) are grown almost entirely for their leaves, not their flowers. The blooms are small and honestly a bit underwhelming compared to the foliage, which can be swirled with silver, burgundy, deep green, pink, and nearly black all on the same leaf. They're rhizomatous, meaning they grow from a thick, horizontal stem that creeps along or just below the soil surface rather than producing a traditional upright trunk or growing from a corm like tuberous types.

That rhizomatous growth habit matters for how you care for them. The rhizome stores water and nutrients, which is part of why overwatering is such a common killer: the plant already has reserves, and a constantly wet rhizome rots fast. Rex types also go through a semi-dormant period in winter when growth slows noticeably, which affects your watering and fertilizing schedule. If you've grown begonia maculata or semperflorens before, set those routines aside, because rex begonias have their own specific requirements. If you specifically want to grow begonia maculata, you will need to adjust the care routine to match its lighter needs and different watering habits.

Light, temperature, humidity, and airflow

Getting the light right

Rex begonias want bright indirect light, and that distinction is important. Direct sun scorches their leaves quickly, leaving papery brown patches that don't recover. Indoors, an east-facing window is ideal because it delivers gentle morning sun without the intense afternoon heat. West-facing windows can work, but hang a sheer curtain to diffuse the light. A south-facing window without a curtain is usually too intense, especially in summer. North-facing windows often don't give enough light and the colors will fade and the plant will stretch toward whatever light it can find.

If you want to move your rex begonia outside in warmer months, find a shaded patio spot or somewhere under a tree canopy. Even morning sun for more than an hour or two can cause scorching outdoors. Dappled shade is the sweet spot. Bring them back inside before nighttime temperatures drop below 60°F, which in most of the US means sometime in September.

Temperature and humidity

Keep rex begonias between 60°F and 80°F. They don't tolerate frost at all, and temperatures below 55°F can cause serious stress or damage. On the upper end, hot and dry conditions above 85°F will invite spider mites and cause leaf curl. Most homes are fine temperature-wise, but humidity is where people run into trouble. Rex begonias want humidity at 50% or higher, which is often significantly more than what most indoor environments provide, especially in winter when heating systems dry out the air.

The tricky part is that you cannot just mist the leaves to raise humidity. Wet foliage left sitting on the plant is a direct invitation to powdery mildew and botrytis (gray mold), both of which are serious problems for rex begonias. Instead, run a humidifier nearby, place the pot on a tray filled with pebbles and water (with the bottom of the pot sitting above the water line, not in it), or group your rex begonia with other plants. Good air circulation is just as important as humidity: stagnant moist air is where fungal problems develop. A small fan on low, pointed away from the plant to keep air moving in the room, makes a real difference.

Potting mix and containers

Rex begonias need a potting mix that drains fast and stays airy. A standard all-purpose potting soil is usually too dense and holds too much moisture for the rhizome. A good starting mix is two parts perlite or coarse sand to three parts peat-based potting mix, or you can use a pre-made mix labeled for African violets, which has a similar texture and pH. The soil pH should be slightly acidic, around 5.7 to 6.5, which is where rex begonias take up nutrients most efficiently.

For containers, clay or terracotta pots are genuinely better for rex begonias than plastic. Clay is porous and lets the soil dry out faster between waterings, which dramatically reduces the risk of root and rhizome rot. Whatever container you choose, it must have drainage holes. No exceptions. The pot size should be just slightly larger than the root mass: rex begonias actually prefer being a little snug in their containers and tend to struggle in pots that are too large because excess soil stays wet for too long.

How to plant and propagate rex begonias

Planting from a nursery purchase or rhizome

If you're starting with a nursery plant, move it into fresh well-draining mix as soon as you get it home. Don't bury the rhizome deeply: it should sit at or just barely below the soil surface. Burying it too deep is one of the most common beginner mistakes and leads directly to rot. If you're starting from a purchased rhizome or offset, lay it horizontally on top of the mix and press it in gently so just the bottom half is in contact with the soil. To get started with how to grow begonia corms, plant the corms in well-draining mix and keep them consistently warm until they sprout.

Leaf propagation: the easiest way to get new plants

Leaf propagation is the most popular method for rex begonias and it's genuinely satisfying once you get the hang of it. There are two main approaches: whole leaf cuttings and leaf wedges.

For a whole leaf cutting, take a healthy medium-sized leaf and cut the main veins on the underside with a sharp, clean blade, making cuts every half inch or so. Then lay the leaf face-up on moist rooting mix (a mix of perlite and peat works well) and use small stones or bent wire to hold the leaf flat against the surface so the cut veins stay in contact with the mix. Tiny plantlets will sprout from each cut within a few weeks.

For leaf wedges, cut a healthy leaf into triangular sections, each with a piece of the central vein included. Press each wedge vein-side down into moist rooting mix. At around 70°F (21°C), wedge cuttings typically root in three to six weeks. Cover the tray loosely with clear plastic to hold humidity, but lift the cover daily for a few minutes to let air circulate and prevent mold.

Propagating from rhizome sections

If your rex begonia has a long rhizome with a bare section (which happens as it ages), you can cut that section into pieces, each about 2 to 3 inches long, and press them horizontally into moist rooting mix. Keep them warm and covered lightly to retain humidity. This method is also useful when you're repotting and find that the rhizome has spread beyond the pot: just pot up the pieces separately. Spring is the best time for rhizome propagation since the plant is putting out new growth and has energy to root quickly.

Watering and fertilizing

How and when to water

Water rex begonias when the top inch of potting mix feels dry to the touch. Stick your finger in: if there's any moisture at that depth, wait another day or two. When you do water, water thoroughly until it drains freely from the bottom, then empty the saucer so the pot isn't sitting in standing water. Some growers prefer bottom watering, where you set the pot in a shallow dish of water for 20 to 30 minutes and let the soil draw moisture up from below, which keeps the surface and rhizome drier. If you want to grow a begonia in water, start by taking a healthy cutting and keeping it clean in a jar until roots form. Either method works well as long as you let the soil approach dryness between sessions.

In winter, when growth slows down, you'll water much less frequently, sometimes only every two to three weeks. The plant isn't actively growing and the soil dries out more slowly. Overwatering in winter is probably the single most common way people lose a rex begonia.

Fertilizing for vibrant color

During the growing season (roughly spring through early fall), feed your rex begonia with a balanced, water-soluble fertilizer diluted to about a quarter of the recommended strength. A fertilizer in the range of 23-19-14 or a balanced 20-20-20 works well. Apply it every two weeks at quarter strength rather than hitting the plant with full-strength fertilizer less often: rex begonias are sensitive to fertilizer burn and the dilute approach keeps feeding consistent without shocking the roots. In late fall and winter, stop fertilizing entirely and let the plant rest.

Ongoing care through the seasons

Pruning and tidying

Rex begonias don't need much pruning in the traditional sense. Most of the maintenance is grooming: removing dead or yellowing leaves as soon as you spot them, and clearing any fallen debris from the surface of the potting mix. This isn't just aesthetic. Dead leaves sitting on the soil are a breeding ground for fungus gnats, botrytis, and other problems. The American Begonia Society specifically recommends removing all surface debris as a basic disease-prevention step, and it really does make a difference.

If your rex has grown upright stems (some varieties are more upright than others) or if the rhizome has stretched long with bare sections and few leaves, you can cut it back. Use clean, sharp scissors or pruning shears and cut the rhizome back to a section that still has healthy growth. The cut rhizome section can itself be used to propagate a new plant.

When and how to repot

Repot rex begonias in spring when you see new growth starting. Signs that it's time: roots circling the bottom of the pot or pushing out the drainage holes, the rhizome pressing against the pot walls, or the plant drying out much faster than usual between waterings. Move up only one pot size at a time. When you repot, take the opportunity to inspect the rhizome: trim off any soft, mushy, or black sections with a clean blade and let the cut surfaces dry for 30 minutes before potting into fresh mix.

Troubleshooting common problems

Powdery mildew deserves a special mention because it shows up so often with rex begonias. The white powdery patches are actually fungal growth on the leaf surface, and the spores spread easily through air currents to infect nearby leaves and plants. The best defense is keeping foliage dry (never mist the leaves), maintaining good airflow around the plant, and removing any infected leaves immediately. Once it's widespread, it's very hard to reverse without a fungicide, so catching it early is key.

Root and stem rot from Pythium and Rhizoctonia fungi look like wilting that doesn't respond to watering, browning at the soil line, or a rhizome that feels soft and smells unpleasant when you dig it out. If you catch it early, cut back to healthy tissue, dust the cuts with powdered cinnamon (a mild natural antifungal), let the cuts dry, and repot into fresh dry mix. Adjust your watering habits immediately: the rot almost always starts from consistently wet soil.

Quick-reference care summary

Rex begonias have a reputation for being fussy, and honestly there is a learning curve. But most of the problems that kill them trace back to just two things: too much water and not enough humidity with too much stagnant air. To get better results, follow a clear weeping begonia routine for light, watering, and humidity similar to what you use for rex begonias, but adjust for its trailing growth habit but most of the problems that kill them trace back to just two things: too much water and not enough humidity. Nail those two, and the rest of the care is pretty manageable. If you are wondering how to grow polka dot begonia, the same focus on bright light and humidity helps you get strong, healthy foliage. If you enjoy growing other begonia types, the rex's needs are quite specific compared to, say, begonia semperflorens or cane types, so treat this as its own plant rather than adapting a general begonia routine. Once you get a healthy rex going, you'll find it's genuinely one of the most rewarding foliage plants you can grow indoors. If you want to apply the same approach outdoors, learn how to grow montbretia in your garden so you can match its light and soil needs. If you're also wondering how to grow a begonia in general, the basics of light, watering, and humidity still matter, but rex begonias need a more specific setup.