Begonia care as a houseplant

Begonias grow well as houseplants when they get bright indirect light, soil that is evenly moist but never soggy, warm rooms around 65-75°F, and humidity raised without wetting the leaves. Each begonia group has its own quirks: rex begonias are fussy about humidity and cold, angel wing types need regular pruning, and tuberous begonias need a winter rest.

There are well over a thousand begonia species and many more hybrids, so the first step is knowing which kind you have. This card covers care for all the main indoor groups. For a field guide to individual varieties, see begonia types.

Begonia groups at a glance

The RHS groups indoor begonias into fibrous-rooted, cane-stemmed, rhizomatous and semi-tuberous types. Clemson Extension divides them into flowering and foliage begonias and adds tuberous, Lorraine (Christmas) and Elatior types.

Colorado State Extension points out that cane begonias have jointed stems with a leaf and/or flower cluster at every joint, and that identifying a cane begonia down to the cultivar is often difficult because there are so many. For care, the group matters far more than the exact name.

Light

• Rex and other foliage begonias: bright indirect light, out of direct sun. An east window or a few feet back from a south window.
• Cane and fibrous flowering types: bright light with a little morning sun; Clemson suggests early morning sun in an east window for flowering begonias.
• All types: hot afternoon sun through glass bleaches and scorches the leaves.

Too little light shows up as long gaps between leaves, small leaves and no flowers. Rotate the pot a quarter turn each week so cane types grow evenly. See light.

Watering

Clemson's guidance is to keep the soil evenly moist, letting it dry only slightly between waterings, and to avoid wet or waterlogged soil. The RHS warns that overwatering is a common cause of loss. In practice:

• Water when the top half inch to inch feels dry.
• Water at the soil, not over the leaves.
• Empty saucers after 15 minutes.
• In winter, water less; rex begonias in particular slow down.
• Tuberous begonias: stop watering in fall as they die back.

Begonia stems and rhizomes are succulent and rot quickly in a heavy, wet mix. If you have killed begonias before, overwatering is the likely reason. More on technique in watering.

Temperature and humidity

Clemson recommends 66-73°F with night temperatures not below 55°F. The RHS gives a minimum of about 55°F for rex and B. masoniana. Begonias dislike cold glass, drafts, and spots right above heat registers.

Humidity is where many growers go wrong. Begonias like humid air, but Clemson specifically says misting is not recommended; mist the air around the plant instead, or better, use other methods:

• A small humidifier near a group of plants; rex begonias benefit most.
• Pebble trays with water below the pot base.
• Grouping plants together.
• Growing small rex begonias in a terrarium or cabinet.

See humidity for details.

Soil and repotting

Use a light, airy mix: peat- or coir-based potting mix with plenty of perlite. Begonias have fine roots and like small pots; move up only 1 inch at a time, usually in spring when roots fill the pot. Rex and other rhizomatous begonias do well in wide, shallow pots. See repotting.

Fertilizer

Clemson recommends a balanced liquid fertilizer at half strength at alternate waterings while the plant is in full growth. Reduce or stop in winter, especially for rex begonias. Too much nitrogen on flowering types gives leaves at the expense of blooms. See fertilizer.

Pruning angel wing and cane begonias

Cane begonias grow tall and lose lower leaves with age. Clemson advises cutting back overly long stems in spring or early summer to encourage new growth at the base; cutting one or two of the oldest canes low each year keeps the plant full. Pinch the tips of young canes to encourage branching. The cuttings root easily.

Powdery mildew and other diseases

Clemson notes diseases are infrequent in the home, but the RHS warns that begonia mildew can be a problem in damp, over-humid conditions, and stem rot follows soggy soil. Powdery mildew looks like white flour dusted on leaves and stems; the leaf tissue beneath can die.

Prevention is mostly cultural:

1. Water at the soil, never over leaves.
2. Do not mist.
3. Give plants space and gentle air movement; a small fan on low helps.
4. Remove dead leaves and spent flowers promptly.

If mildew appears, cut off the worst leaves, isolate the plant, and use a fungicide labeled for houseplants or ornamentals if it continues to spread. For general symptom checklists see leaf spots and root rot.

Pests include mealybugs, spider mites, thrips, scale and whiteflies. Treatment guides: mealybugs, spider mites, thrips.

Propagation

The RHS recommends leaf cuttings in late spring for rhizomatous types, stem cuttings in spring for fibrous and cane types, and division of rhizomatous plants in spring.

Stem cuttings (cane, fibrous): the RHS suggests 3-4 inch cuttings in April, inserted in a sandy, peat-free cuttings mix with bottom heat of 64-70°F. Remove the lower leaves first; cane types also root in water.

Leaf cuttings (rex):

1. Take a healthy mature leaf.
2. Cut the leaf stalk off and, with a sharp blade, cut through the major veins about 1 inch apart (RHS).
3. Lay it flat on moist mix and pin it down so the cuts touch the soil.
4. Cover with a clear lid; keep warm and bright.
5. Plantlets form at the cuts over the following weeks; be patient and keep the mix only lightly moist.

See propagation for more methods.

Tuberous begonias: keeping tubers over winter

Tuberous begonias are summer plants. In fall, as days shorten, reduce water and let the foliage die back. Clemson suggests storing tubers over winter in dry peat moss in a cool place. Lift the tubers, let them dry, brush off soil, and keep them somewhere cool and frost-free. In late winter, set them hollow side up in moist mix in a warm, bright spot to restart.

Are begonias toxic to pets?

Yes. The ASPCA lists begonia as toxic to cats, dogs and horses. The toxic principle is soluble calcium oxalates; the ASPCA lists vomiting and salivation in dogs and cats and notes the underground parts are the most toxic. Keep plants and especially stored tubers away from pets. If ingestion happens, call your vet or the ASPCA Animal Poison Control Center at (888) 426-4435; for children, Poison Control at 1-800-222-1222. See toxic plants.

Seasonal care calendar

Buying a begonia

• Check leaf undersides and stems for mealybugs and white mildew patches before buying; both are common in greenhouses.
• Avoid plants with soft or blackened stems at the soil line.
• For rex begonias, pick plants with several new leaves unfurling at the rhizome tip.
• Rieger and other florist begonias are bred for a long show of flowers; enjoy them for months, but do not expect them to perform like a permanent houseplant.
• Keep new begonias apart from others for a couple of weeks to watch for pests and mildew.

Begonias outdoors in summer

Many US growers move cane and fibrous begonias to a shaded patio for summer, where humidity and air movement help them. Move them out when nights stay above 55°F, keep them in bright shade, and bring them back before temperatures drop to 55°F in fall. Check for pests before bringing them in.

Common mistakes

1. Misting for humidity. It is the most common cause of powdery mildew on indoor begonias.
2. Large pots of dense soil. Fine begonia roots rot in wet, heavy mix.
3. Direct afternoon sun on rex begonias. Their colorful leaves scorch quickly.
4. Treating all begonias the same. Tuberous types need a winter rest; rex types need humidity; cane types need pruning.
5. Never pruning angel wings. Without renewal cuts they become a few tall bare canes.
6. Watering a resting rex begonia like a growing one. In winter it uses far less water; let the surface dry a little more between waterings.

Choosing a begonia for your home

• Brightest east window, humidifier running: rex begonias.
• Bright room, want flowers most of the year: angel wing or other cane begonias.
• Normal light, little fuss: fibrous types such as B. metallica.
• Winter gift plant: Rieger begonia; enjoy it for the season.

For more flowering options see flowering houseplants.