Bulb · Begoniaceae
Tuberous Begonia
Begonia × tuberhybrida
Offer 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
People grow the tuberous begonia for its flowers, which rank among the largest and most colorful that any shady spot can produce. Rather than rising from fibrous roots, it grows from a plump underground tuber, and that tuber holds the secret to it all: it fuels a long summer of flowering, then naps through winter, ready to wake again. A bed, a pot, or a hanging basket all suit it just fine.
Warm-season by nature, these dislike frost and fierce sun in equal measure, which is what makes them such a treat for the shade gardener's flower. Their colors stretch from gentle pastels to deep reds, and their shapes range from camellia-style doubles to trailing forms that tumble from a basket. Most keep a tidy size, growing 12 to 24 inches (30 to 61 cm) tall.
Truly, none of this is difficult once you honor two simple things. Soggy soil rots the tuber, so good drainage and a measured touch with the watering can will largely decide how well the plant thrives. Sort out the light and the water, and it carries big blooms from midsummer to frost.
Care
The short version: partial to dappled shade, soil that stays evenly moist yet never soggy, rich and well-drained ground, and a cool, breezy place that keeps the foliage dry and free of disease.
Light
Offer them partial to dappled shade, that soft glow you find beneath a tree or along the cooler side of the house. A little gentle morning or late-afternoon sun is welcome, but harsh midday sun scorches the leaves and slows the flowering.
Water
Aim to keep the soil evenly moist but never soggy, watering every 2 to 4 days once the surface begins to dry. Remember the tuber holds its own water reserve, so a waterlogged pot rots it from underneath. Let the top dry a little between drinks and you'll be on the right track.
Soil
Settle them into rich, well-drained loam with a good helping of organic matter mixed through. A pH from 5.5 to 7.0 keeps them content, and sharp drainage is the detail that matters most, since standing water is what claims the tuber.
Temperature
They feel their best between 55°F and 75°F (13°C to 24°C). Heat beyond that range wears on the plant and drops the buds, while frost brings the season to a close.
Humidity
Ordinary household humidity is plenty, so there's no figure to fuss over. Airflow matters far more than moisture in the air, because still, damp conditions are precisely what mildew and gray mold love.
Feeding
Count on these being heavy feeders. All through the growing season, from spring into late summer, offer a dilute balanced fertilizer roughly every two weeks to keep those generous flowers coming.
Pruning
Pinch the growing tips early to encourage bushier growth and more blooms, and gently remove spent flowers as they fade. When late summer comes around, trim the plant back and ease off the watering to guide it kindly into dormancy.
Repotting
Work with them on a yearly rhythm. Lift the tubers each fall, keep them cool and dry through the winter, then start them fresh in new medium come spring instead of letting them languish in worn, crowded soil.
Size & spacing
Plants grow 12 to 24 inches (30 to 61 cm) tall and reach 12 to 18 inches (30 to 46 cm) across. Give each one that much breathing space so air can flow and the leaves stay dry.
When to plant
Tuberous begonias follow a tidy yearly rhythm that revolves around the tuber. Wake the tubers indoors in late winter, wait until the last frost is safely behind you before setting plants out, and then savor the flowers from midsummer right up to the cold that lulls 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
Nearly all begonia troubles come back to one of two things: water or tired air. Keep a kind eye on the tuber, the lower leaves, and the flowers, since the earliest clues show up there. Find what matches your plant below, and act sooner rather than later.
A soft, mushy tuber or a rotting stem base
Of everything that can trouble these plants, tuber rot is the one to take seriously, and it nearly always comes down to watering too generously. A bad odor, plus wilting even though the soil feels damp, gives it away. Don't lose heart: gently lift the tuber, trim off the rotted parts, dust those cuts, 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
What you are seeing is powdery mildew, a fungus that moves in when air goes stagnant around plants packed too close together. You can wipe the coating away, yet it returns until the plant gets room to breathe. Open up the spacing, water down at the soil, and take off the most affected leaves. This is very fixable.
Fix:
- Improve air circulation and spacing
- Remove and discard affected foliage
- Avoid wetting the leaves when watering
Fuzzy gray mold settling on flowers and leaves
Botrytis blight, which many gardeners call gray mold, gets going in cool, damp, still air, traveling on wet foliage and dropped petals. The touched tissue browns and sinks in quickly. The remedy is simple enough: clear out the moldy bits along with any litter, then open the plant so its leaves dry between waterings.
Fix:
- Remove infected flowers and leaves promptly
- Increase air circulation and reduce leaf wetness
- Clean up fallen plant debris
Buds turn yellow and drop before opening
Think of bud drop as the plant telling you it feels stressed, most often from uneven watering or a spell of heat and humidity. Aim to keep the soil steadily moist, neither flooded nor parched. Once you move it somewhere cooler, shadier, and breezier, the plant relaxes and holds onto the buds that follow.
Fix:
- Maintain even soil moisture without extremes
- Provide shade during hot afternoons
- Move container plants to a cooler, protected spot
Toxicity
Treat this as a toxic plant and keep it away from pets and children. Each part carries soluble calcium oxalates, and the buried tuber holds the most of all. A single bite brings a burning mouth, heavy drooling, and vomiting, so set the plant, and any cut tubers in particular, somewhere well out of reach.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds · People
Cats Mild
If a cat nibbles the foliage or the tuber, its mouth burns and the drooling comes on quickly. Watch for vomiting and pawing at the face soon after.
Dogs Mild
A dog that chews any part may drool, fuss at a sore mouth, and vomit. Since the buried tuber holds the strongest toxin, the diggers are the ones to keep an eye on.
Horses Moderate
Grazing leads to the familiar sore mouth and drooling, though a big mouthful matters more for a horse and can strain the kidneys toward failure.
Rabbits Mild
Those same oxalates sting a rabbit's mouth and put it off eating. Tuck cut tubers and trimmings somewhere it cannot reach.
Livestock Moderate
A nibble leaves cattle, goats, and sheep with a sore, drooling mouth, and a heavy graze on the tubers can put pressure on the kidneys.
Birds Caution
Information on birds is thin, yet the calcium oxalates that bother other animals are reason enough to keep this plant away from them.
People Caution
No part of this plant belongs on a plate, and the sap and tubers can leave skin and mouth irritated. Rinse your hands after handling, and set the plant beyond the reach of little ones.
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
You will find tuberous begonias in many different flower forms, and just a few groups account for most of what crosses your path. Here are the ones it helps to know by name.
Camellia (Camelliflora) types
If you want the most striking blooms in the group, these deliver: full, double, and reaching 3 inches across, with the look of a camellia.
Picotee types
A slim ribbon of contrasting color rims every double flower, giving the petals a neatly outlined edge.
Pendula (hanging/trailing) types
Rather than growing upward, these let their stems cascade over a pot rim, which is exactly what makes them perfect for hanging baskets.
How to propagate
There are three friendly ways to grow more of these plants: dividing a tuber, rooting a cutting, or taking the patient route of starting from seed.
DivisionModerate
Spring when restarting dormant tubers · Several weeks to sprout and root
When spring rolls around and the dormant tubers begin to stir, slice one into pieces so that each piece holds at least one shoot. Be sure to dust every cut surface, because a fresh wound on a tuber gives rot an easy opening. Allow several weeks for each division to sprout and root before it finds its feet.
Stem cuttingsModerate
Spring as new shoots develop · 3 to 6 weeks to root
As spring brings fresh shoots, snip a basal or stem cutting and settle it into a moist, well-drained mix away from direct sun. Allow 3 to 6 weeks for it 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
Growing from seed asks the most patience. Because the seed is as fine as dust, sprinkle it across the surface and keep things warm and humid instead of covering it. Sow in December or January, and plan 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.
According to the ASPCA, begonia counts as toxic to cats, dogs, and horses because of soluble calcium oxalates, with the hidden tuber being the most toxic part of the whole plant. An animal that chews it ends up with a sore mouth, plenty of 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 grow unhappy in hot, direct sun, which scorches their leaves and knocks off the buds. Just a touch of soft morning or late-afternoon light is all they wish to take.