Tuberous begonia

Tuberous begonia: how do you recognise it?

Habit

Compact, upright or trailing plant 25–30 cm tall and as wide, with fleshy, juicy and rather brittle stems.

Leaves

Lopsided, heart-shaped to oval leaves with a toothed edge, wider on one side than the other; fresh to dark green, sometimes with a bronze tint.

Flower

Large, often double male flowers, usually with smaller, single female flowers beside them, from June to September.

Colour

Red, orange, yellow, pink, salmon and white, sometimes bicoloured or with a coloured edge.

Tuber

Flat, brown tuber with a hollow top, where the shoots emerge, and a rounded underside.

Flowering: June–September · Plants: May–June

Why grow it?

• Generous flowering from June to September, even in partial and light shade.
• Large, often double flowers in bright or soft colours.
• Ideal for pots, containers and hanging baskets on a north- or east-facing patio.
• The tubers last for years if you overwinter them frost-free.
• A colourful eye-catcher in a dark corner of the garden or on a balcony with little sun.

Tuberous begonia: where does it grow best?

• Partial or light shade: morning sun is fine, full midday sun scorches leaves and flowers.
• Humus-rich, open, well-drained soil; acid to neutral potting compost is ideal.
• Evenly moist, but never soggy.
• Sheltered from wind and heavy rain, as the stems are brittle and the flowers heavy.
• Allow 25–30 cm between plants; a 20–25 cm pot holds one tuber.

Light

Partial shade and shade

Soil type

Sand, loam or peat

Acidity

Acid or neutral

Moisture

Normal

Size

0.3 m tall, 0.3 m wide

Hardiness

Frost tender: lift the bulbs or tubers before the frost and store them frost-free

Goes well with

• Fuchsia: Likes the same partial shade and flowers just as long.
• Busy Lizzie: A low, colourful edging in the shade.
• Ferns: Fine green fronds that make the large flowers stand out.
• Hosta: Large, calm leaves beside the bright colours.

Tuberous begonia: when and how to plant it?

Plant in May–June.

1. In March, set the tubers indoors, hollow side up, on moist potting compost, in a light room at 15–20 °C.
2. Barely cover them: the top stays just visible or gets at most a thin layer of compost.
3. Pot each one up separately once the shoots are about 5 cm long.
4. Harden them off in May: outdoors by day, indoors at night.
5. Plant out after mid-May in partial shade, 25–30 cm apart, at the same depth as in the pot.
6. Water in, and from then on water the soil, not the leaves.

Care

Watering

Keep the soil evenly and slightly moist and never leave water standing in the saucer. Water the soil, preferably in the morning.

Feeding

From June to August, a flowering-plant fertiliser every two weeks.

Deadheading

Remove faded flowers and yellow leaves: this helps prevent grey mould.

Support

Large-flowered varieties need a thin cane, as the stems are brittle.

Bigger flowers

For the largest blooms, pinch off the small female flowers beside the large male ones.

Tip: Always water the soil, preferably in the morning: leaves and flowers that stay wet overnight are the main cause of disease in begonias.

Tuberous begonia: when to prune it?

When: No pruning is needed. Remove faded flowers and damaged stems throughout the summer.

How:

• Cut or pinch off faded flowers together with their stalks.
• Remove yellow or mouldy leaves straight away.
• Cut broken stems back to just above a healthy leaf.

Caution: Do not cut the stems off while still green in autumn: let them die back naturally after bringing the plants in, so the reserves return to the tuber.

Pruning calendar and basic rules

Propagation

Dividing tubers

In March–April, when the tubers start into growth, cut large tubers into pieces, each with at least one shoot. Let the cut surfaces dry for a day before potting.

Cuttings

In spring, cut young shoots 8–10 cm long with a small piece of tuber at the base and root them in moist cuttings compost. They form a small tuber the same summer.

Tuberous begonia: how does it get through the winter?

Hardy to 2 °C: protect in harsh winters.

• Not hardy: frost kills the plant and freezes the tuber.
• In October, before the first frost, lift the plants with their root ball and let them die back in a frost-free place.
• Remove the stems once they come away easily, let the tubers dry and store them in a box of dry sand at 5–10 °C.
• Bring plants in pots, pot and all, into a cool, frost-free place and stop watering.

Diseases and pests

• Powdery mildew: White powder on the leaves, especially in late summer. Give the plants space and fresh air and cut off affected leaves.
• Grey mould: Grey fluff and rotting flowers and stems in damp weather. Remove faded flowers and do not water over the leaves.
• Tuber rot: A soft, rotting tuber and a plant that suddenly collapses. The cause is too much water: water less and use open compost.
• Vine weevil: The grubs eat tubers and roots, especially in pots, and the plant suddenly wilts. Check the root ball and, if needed, use nematodes against the grubs.
• Bud drop: Buds fall off with irregular watering or sudden changes in temperature. Water regularly.

Through the year

• January: Check stored tubers.
• March: Start tubers indoors, hollow side up.
• April: Pot up sprouted tubers. Take cuttings.
• May: Harden off. After mid-May, plant out in partial shade.
• June: First flowers. Feed every two weeks.
• July: Full flower. Remove faded flowers.
• August: Flowering. Watch out for powdery mildew.
• September: Last flowers. Stop feeding.
• October: Bring in before the first frost and let them die back.
• November: Clean the tubers and store them dry at 5–10 °C.

Edible and useful

Not edible. All begonias are poisonous, especially the tubers and roots: they contain oxalates which, when chewed, cause a burning feeling and irritation of the mouth and throat, with drooling and vomiting, in children as well as in cats and dogs; grazing animals and rabbits can fall ill from them too. Tuberous begonias overwinter dry in a box or pot: store the tubers out of reach of children and pets, and not with the potatoes. Indoor begonias often stand on the windowsill, at a child’s height and within a cat’s reach: put them higher up or in another room. The flowers of tuberous begonia sometimes appear on lists of edible flowers, but because of the oxalates they are best not eaten, especially if you have kidney stones. If any is swallowed, call a poison centre (in Belgium 070 245 245) or your doctor at once.

Did you know?

• The genus Begonia is named after Michel Bégon, a 17th-century French official who supported botany.
• A begonia carries separate male and female flowers. You can recognise the female ones by the winged ovary behind the flower.
• Every two years a huge flower carpet is laid on the Grand-Place in Brussels, traditionally made largely of begonias. The region around Ghent has long been a major centre of begonia growing.