Most varieties grow best in a mild temperature range, between 15°C and 26°C, though tuberous begonias need it a little cooler to perform at their best. They like humidity and warmth, but can’t tolerate extreme heat, dryness or frost.
As a general rule, begonias favour bright filtered light with no exposure to harsh midday sun. Some species will also tolerate deep shade. They need good ventilation to help prevent fungal diseases and do well planted under trees and shrubs. Some of the cane-stemmed and wax varieties will tolerate full sun.
In the garden, they require free- draining soil improved with compost. Heavy clay soil that becomes waterlogged is unsuited, as it can cause root and stem rot. In pots, use a light free- draining potting mix containing coco coir, perlite or vermiculite (African violet mix works well).
Begonias have fleshy stems and leaves that hold water for long periods of time, so they don’t need constant watering. Too much water can cause plants to turn brown and rot, so allow them to dry out almost completely between waterings. Try to water the soil around the plant and not the foliage, as wet leaves can encourage powdery mildew.
For potted plants, apply a general-purpose slow-release fertiliser at the time of potting and liquid fertiliser at half-strength every two to three weeks during the growing period. In the garden, it’s advisable to incorporate a general-purpose fertiliser into the soil at planting time.