Bulb · Begoniaceae
Tuberous Begonia
Begonia × tuberhybrida
Offer it shade, even moisture, and good airflow, and the tuberous begonia rewards a summer room with its largest blooms.
Partial shade
Every 2–4 days
55–75°F · 13–24°C
98–120 days
Overview
The tuberous begonia earns a spot in the home for its flowers, which rank among the fullest and most luxurious that a shaded corner can hold. Its growth rises from a plump underground tuber rather than a fibrous root, and that tuber sets the rhythm of the whole season: it fuels a long stretch of summer color, then settles into rest through the cold months, ready to begin once more. Bed, pot, or hanging basket, it adapts to the setting you give it.
Warm-season by nature and unfriendly to both frost and glaring sun, this is the kind of plant that suits a sheltered, shaded spot, very much a shade gardener's flower. The color story moves from quiet pastels to deep, saturated reds, and the forms run from camellia-style doubles to trailers that drape over a basket edge. Most keep a tidy frame, standing 12 to 24 inches (30 to 61 cm) tall, which makes them easy to place.
None of this asks for much once two points are honored. The tuber will rot in waterlogged soil, so drainage and a measured hand at the watering can quietly decide whether the plant thrives. Settle the light and the water, and it carries big blooms from midsummer to frost, an anchor of color for a shaded patio or a north-facing room.
Care
The short version: partial to dappled shade, soil held evenly moist yet never waterlogged, rich and free-draining ground, and a cool, breezy corner that keeps the foliage dry and free of disease.
Light
Set them in partial to dappled shade, the soft, filtered light found beneath a tree or along the cool side of a house. A little gentle morning or late-afternoon sun is welcome, but harsh midday sun scorches the leaves and stalls the flowers.
Water
Keep the soil evenly moist but never soggy, reaching for the can every 2 to 4 days as the surface begins to dry. The tuber holds its own reserve of water, so a drenched pot rots it from beneath. Let the top dry a touch between drinks.
Soil
Give them rich, well-drained loam with a generous helping of organic matter worked through. A pH from 5.5 to 7.0 suits them well, and sharp drainage is the detail that counts most, since standing water is what undoes the tuber.
Temperature
They are at their best between 55°F and 75°F (13°C to 24°C). Heat beyond that range strains the plant and drops its buds, while frost closes the season for good.
Humidity
Average humidity is plenty, so there is no figure to chase. Airflow matters far more than moisture in the air, since the still, damp pockets are precisely what mildew and gray mold are waiting for.
Feeding
These are heavy feeders. All through the growing season, from spring into late summer, offer a dilute balanced fertilizer roughly every two weeks to keep the big flowers arriving.
Pruning
Pinch the growing tips early to encourage bushier growth and more blooms, and lift away spent flowers as they fade. When late summer comes, cut the plant back and ease off the water to walk it gently into dormancy.
Repotting
Keep them on a yearly cycle. Lift the tubers each fall, store them cool and dry through winter, then start them in fresh medium come spring rather than leaving them in spent, crowded soil.
Size & spacing
Plants stand 12 to 24 inches (30 to 61 cm) tall and reach 12 to 18 inches (30 to 46 cm) across. Allow each one that much space so the air moves freely and the leaves stay dry.
When to plant
Tuberous begonias keep to a yearly rhythm shaped by the tuber. Wake the tubers indoors in late winter, move the plants outside only once the last frost has cleared, and let the display run from midsummer until the chill sends the tuber back into rest.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Sow: Start tubers indoors February to April; sow seed December to January for summer bloom
- Plant: After all danger of frost passes, typically late May to early June
- Harvest: Mid-summer through first frost (July to September)
Hardiness
USDA hardiness zones: 9–11
Temperature: down to -7°C
Troubleshooting
Most of what troubles a begonia comes down to water or stagnant air. Keep an eye on the tuber, the lower leaves, and the flowers, since those are where the earliest signs show. Find your match below and act before it spreads.
A spongy tuber or a stem base going to rot
Tuber rot is the worst fate that can befall one of these plants, and the cause is nearly always water sitting where it should not. The signals are a sour odor and wilting that persists even when the soil feels damp. Lift the tuber, pare away the rot, dust the cuts, and settle it back into a fresh, quick-draining mix.
Fix:
- Reduce watering immediately
- Lift and inspect the tuber; cut away rotted tissue and dust cut surfaces
- Repot or replant in fresh, well-drained medium
A dusty white film creeping across the foliage
What you are seeing is powdery mildew, a fungus that moves in wherever the air goes flat around plants packed too closely together. You can wipe the coating away, but it returns until the plant gets room to breathe. Open up the spacing, water low at the base, and clear off the worst of the foliage.
Fix:
- Improve air circulation and spacing
- Remove and discard affected foliage
- Avoid wetting the leaves when watering
A fuzzy gray mold settling on blooms and leaves
Botrytis blight, the gray mold, finds its footing in cool, damp, motionless air and arrives by way of wet leaves and dropped petals. The tissue it touches browns and folds in quickly. Strip out the moldy growth along with any litter, then loosen the plant so its leaves dry off between waterings.
Fix:
- Remove infected flowers and leaves promptly
- Increase air circulation and reduce leaf wetness
- Clean up fallen plant debris
Buds yellowing and dropping before they open
Bud drop is how the plant registers stress, most often from uneven watering or a run of heat and humidity. Aim for soil that stays evenly moist without flooding or drying to a crust. Move it somewhere cooler, shaded, and breezy, and the plant calms down so the next set of buds holds on.
Fix:
- Maintain even soil moisture without extremes
- Provide shade during hot afternoons
- Move container plants to a cooler, protected spot
Toxicity
This is a plant to keep at a remove from pets and children. Every part carries soluble calcium oxalates, and the hidden tuber is the most toxic piece of all. A single bite brings a burning mouth, heavy drooling, and vomiting, so set the plant, and above all any cut tubers, well beyond reach.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds · People
Cats Mild
Should a cat nip at the leaves or the tuber, its mouth burns and the drooling comes on fast. Vomiting and pawing at the face tend to come next.
Dogs Mild
A dog that chews any piece can be left drooling, sore in the mouth, and prone to vomiting. Because the buried tuber holds the most toxin, the diggers are the ones worth keeping an eye on.
Horses Moderate
A graze leaves the familiar mouth irritation and drooling, yet a large amount weighs more heavily on a horse and can drive the kidneys toward failure.
Rabbits Mild
Those same oxalates sting a rabbit's mouth and put it off its food. Stow cut tubers and trimmings somewhere it cannot reach.
Livestock Moderate
Cattle, goats, and sheep end up with a sore mouth and drooling after a nibble, and a heavy feed on the tubers can tax the kidneys.
Birds Caution
Little is on record for birds, though the calcium oxalates that bother other animals make this one to keep well away from them.
People Caution
No part of this plant belongs on a plate, and the sap and tubers can leave skin and the mouth irritated. Wash up after handling and set it beyond the reach of young children.
Wash hands after handling tubers and sap, which can irritate skin; keep tubers and plants away from pets and children.
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
Tuberous begonias arrive in a broad spread of flower forms, and a handful of groups account for most of what you will come across. These are the ones worth recognizing by name.
Camellia (Camelliflora) types
The most dramatic blooms in the group belong here, full and double and as wide as 3 inches, with the look of a camellia.
Picotee types
A slim band of contrasting color rims each double flower, giving the petals a neatly outlined finish.
Pendula (hanging/trailing) types
Rather than holding themselves upright, these let their stems cascade past the rim of a pot, which makes them the pick for hanging baskets.
How to propagate
There are three ways to grow your stock, ranging from splitting a tuber to rooting a cutting to the patient work of raising plants from seed.
DivisionModerate
Spring when restarting dormant tubers · Several weeks to sprout and root
Come spring, while you are coaxing the dormant tubers awake, divide one so that every piece holds at least one shoot. Dust the cut faces, because an open wound on a tuber invites rot in. Allow each division several weeks to sprout and root before it finds its stride.
Stem cuttingsModerate
Spring as new shoots develop · 3 to 6 weeks to root
As the new shoots rise in spring, snip a basal or stem cutting and tuck it into a moist, well-drained mix kept out of direct sun. Allow it 3 to 6 weeks to root and become a plant of its own.
SeedDemanding
December to January for summer bloom · 14 to 16 weeks before ready to plant out
Seed is the demanding route. The grains are as fine as dust, so scatter them over the surface and hold them warm and humid instead of burying them. Sow in December or January and reckon on 14 to 16 weeks before the seedlings are ready to plant out for summer bloom.
Myths
Begonias are perfectly safe houseplants for homes with pets.
The ASPCA lists begonia as toxic to cats, dogs, and horses on account of soluble calcium oxalates, with the buried tuber the most toxic part of the whole plant. Any animal that chews it ends up with an irritated mouth, heavy drooling, and vomiting. Keep the plant, and especially the tubers, out of reach of animals that chew.
Tuberous begonias need plenty of full sun to bloom well.
The truth runs the other way. These plants want partial to dappled shade and turn sulky in hot, direct sun, which scorches their leaves and drops their buds. A touch of soft morning or late-afternoon light is the most they wish to take.