Bulb · Begoniaceae
Tuberous Begonia
Begonia × tuberhybrida
Hand it shade, even moisture, and good airflow, and the tuberous begonia rewards you with enormous summer blooms.
Partial shade
Every 2–4 days
55–75°F · 13–24°C
98–120 days
Overview
What wins a spot for the tuberous begonia is the flowers, easily among the biggest and richest any shade garden can pull off. It springs from a plump underground tuber instead of a fibrous root, and that tuber drives the whole show: it fuels a long summer of bloom, then rests through winter, primed to fire up again. Plant it in a bed, drop it in a pot, or hang it in a basket.
Warm-season through and through, these plants shun frost and scorching sun alike, which makes them a true shade gardener's flower. They sweep the color range from soft pastels to deep reds, in shapes from camellia-like doubles to trailing forms that pour over a basket edge. Most keep things compact, topping out at 12 to 24 inches (30 to 61 cm) tall.
Pull it off and it isn't hard, as long as you mind two things. The tuber rots in soggy soil, so good drainage and a measured hand on the watering can will decide whether it thrives. Nail the light and the water, and it pumps out big blooms from midsummer to frost.
Care
The short version: partial to dappled shade, soil kept evenly moist but never soggy, rich and well-drained ground, and a cool, breezy spot so the foliage stays dry and disease-free.
Light
Hand them partial to dappled shade, that soft glow under a tree or along the cool flank of the house. They will take a little gentle morning or late-afternoon sun, but blazing midday sun sears the leaves and stalls the flowers.
Water
Hold the soil evenly moist but never soggy, watering every 2 to 4 days as the surface begins to dry. The tuber banks its own water, so a drenched pot rots it from underneath. Let the top dry slightly between drinks.
Soil
Set them in rich, well-drained loam with plenty of organic matter dug through. A pH from 5.5 to 7.0 suits them well, and sharp drainage is what counts most, since standing water is exactly what kills the tuber.
Temperature
They thrive between 55°F and 75°F (13°C to 24°C). Heat past that band stresses the plant and shakes loose the buds, and frost shuts the season down cold.
Humidity
Average humidity does the job, so skip chasing a number. Airflow counts for far more than moisture in the air, because still, damp conditions are precisely what mildew and gray mold need to dig in.
Feeding
These plants are heavy feeders. Right through the growing season, spring into late summer, feed a dilute balanced fertilizer about every two weeks to keep those big flowers rolling.
Pruning
Pinch the growing tips early to drive bushier growth and more blooms, and pluck spent flowers the moment they fade. As late summer rolls in, cut the plant back and taper the water to ease it into dormancy.
Repotting
Run them on a yearly loop. Lift the tubers each fall, store them cool and dry through winter, then fire them up in fresh medium come spring rather than leaving them stuck in tired, crowded soil.
Size & spacing
Plants climb to 12 to 24 inches (30 to 61 cm) tall and fan out 12 to 18 inches (30 to 46 cm) wide. Grant each one that much elbow room so air flows freely and the leaves stay dry.
When to plant
Tuberous begonias run on a yearly rhythm centered on the tuber. Kick the tubers off indoors in late winter, move the plants outside only once the last frost clears, and ride the bloom from midsummer right up until cold weather puts the tuber back to sleep.
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
Trouble with begonias nearly always comes down to water or stale air. Keep tabs on the tuber, the lower leaves, and the flowers, because that's where the earliest clues surface. Match what you spot below and act fast.
A mushy tuber or a stem base going soft
Nothing wrecks these plants faster than tuber rot, and water is nearly always behind it. A sour smell plus wilting in soil that's still damp gives it away. Pull the tuber up, trim out the rot, dust the cuts clean, and tuck it back into 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 leaves
You are looking at powdery mildew, a fungus that moves in wherever the air goes stagnant around packed plants. Rub the coating off and it returns, again and again, until the plant finally gets to breathe. Open up the spacing, aim water at the soil, and snap off the worst leaves.
Fix:
- Improve air circulation and spacing
- Remove and discard affected foliage
- Avoid wetting the leaves when watering
Fuzzy gray mold spreading over flowers and leaves
Botrytis blight, the gray mold, grabs hold in cool, damp, still air and hitches a ride on wet foliage and dropped petals. The tissue it touches browns and caves in quickly. Strip out the moldy growth and any litter, then open the plant up so leaves dry fully 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 signals a stressed plant, and the usual triggers are erratic watering or a spell of heat and humidity. Hold the soil steady at evenly moist, neither flooded nor parched. Shift the plant somewhere cooler, shaded, and breezy, and the next flush of buds will hang on.
Fix:
- Maintain even soil moisture without extremes
- Provide shade during hot afternoons
- Move container plants to a cooler, protected spot
Toxicity
This plant is toxic, so steer it away from pets and children. Every part carries soluble calcium oxalates, and the buried tuber packs the most of all. One bite triggers a burning mouth, heavy drooling, and vomiting, so keep the plant, and any cut tubers especially, well out of reach.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds · People
Cats Mild
Bite into a leaf or tuber and a cat ends up with a burning mouth and a sudden rush of drooling. Vomiting and pawing at the face tend to come next.
Dogs Mild
Chewing any piece leaves a dog drooling, sore in the mouth, and likely to vomit. Since the buried tuber packs the most toxin, keep a sharp eye on dogs that like to dig.
Horses Moderate
Grazing delivers the same mouth irritation and drooling, yet a big mouthful hits a horse harder and can drive the kidneys toward failure.
Rabbits Mild
Those oxalates sting a rabbit's mouth too and put it off its food. Stash cut tubers and trimmings far out of reach.
Livestock Moderate
A nibble gives cattle, goats, and sheep a sore mouth and drooling, while a heavy graze on the tubers can tax the kidneys.
Birds Caution
Reports on birds are thin, yet the calcium oxalates that bother other animals make this one to keep well clear of them.
People Caution
No part belongs on a plate, and the sap and tubers can irritate skin and mouth alike. Wash your hands after handling and keep the plant clear of small 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 span a wide spread of flower forms, and a handful of groups cover most of what you'll run into. Here are the ones worth knowing by name.
Camellia (Camelliflora) types
Bloomwise these top the group: full, double flowers up to 3 inches across that read almost dead-on like a camellia.
Picotee types
A slim band of a contrasting shade rims every double flower, giving the petals a crisply outlined look.
Pendula (hanging/trailing) types
Rather than growing upright, these send their stems cascading over the pot's rim, which makes them the pick for hanging baskets.
How to propagate
Three routes let you grow your stock, from splitting a tuber to rooting a cutting to the slow grind of starting from seed.
DivisionModerate
Spring when restarting dormant tubers · Several weeks to sprout and root
As spring wakes the dormant tubers, slice one up so each section holds at least one shoot. Dust those cut faces, because an open wound on a tuber hands rot an easy entrance. Every piece needs several weeks to sprout and root before it really takes off.
Stem cuttingsModerate
Spring as new shoots develop · 3 to 6 weeks to root
When fresh shoots break ground in spring, snip a basal or stem cutting and nestle it into a moist, well-drained mix out of direct sun. Allow 3 to 6 weeks for it to root into a plant of its own.
SeedDemanding
December to January for summer bloom · 14 to 16 weeks before ready to plant out
Seed is the toughest route by far. The seed runs as fine as dust, so sprinkle it across the surface and hold it warm and humid instead of covering it. Sow it in December or January and plan on 14 to 16 weeks before the seedlings are set to plant out for summer bloom.
Myths
Begonias are perfectly safe houseplants for homes with pets.
ASPCA flags begonia as toxic to cats, dogs, and horses on account of soluble calcium oxalates, and the hidden tuber carries the heaviest load of all. Chew on it and a pet winds up with a sore mouth, streaming drool, and vomiting. Keep the plant, and the tubers most of all, out of reach of animals that chew.
Tuberous begonias need plenty of full sun to bloom well.
Flip that around. These plants crave partial to dappled shade and turn sullen in hot, direct sun, which scorches leaves and knocks off buds. A touch of soft morning or late-afternoon light is all they want.