How to grow begonias
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.
Cane stemmed begonias
Tall growing, up to 1-2m, these varieties bloom from mid-summer to mid-autumn with fleshy flowers like little chandeliers, in shades of pink, red, orange and white. One of the most popular is B. coccinea, which has pendulous heart-shaped leaves with red undersides and margins. They’re stately plants, great for filling areas of the garden that need a vertical element. Or try them as specimen plants in large pots, on a verandah or in a courtyard.
These are robust plants; they come in many sizes, colours and leaf shapes, and bear flowers for many months. They can handle being a little on the dry side and prefer semi-shade. A few standouts in the group are Begonia venosa, with rounded silver-grey velvety leaves, B. metallica, with purple-veined leaves, and the majestic B. luxurians, with leaves that look almost like a palm frond – green on the topside and red underneath. Unlike the cane-stemmed varieties, shrub begonias will branch, so prune in late winter to promote new growth.
Renowned for amazing glasshouse displays, begonia tuberhybrida, or tuberous begonias, have gorgeous double flowers that appear in late spring and summer. They make delightful pot or window box displays. Best in filtered shade, they like a little morning sun in cooler climates. Allow the potting mix to dry out between waterings and store the pots somewhere dry over winter.
Ideal as houseplants or in hanging baskets, elatior begonias (Begonia x hiemalis) are short-lived but flower prolifically and come in fabulous colours, from hot reds and oranges to softer sherbet-like pinks, lemons and apricots. A group of two or three pots of these little beauties will brighten any room. In terms of growing, they like rich, well-drained soil and detest soggy feet. Grow them in African violet potting mix and keep it evenly moist. Cut back spent flower stems to 5–10cm long, to revitalise the plant and encourage new growth.
Also known as king begonias, Rex begonias have the name for good reason. While their flowers are insignificant, their foliage is like a royal robe with purple, pink, maroon, pewter, silver and shades of green splashed on the foliage in dazzling combos. They grow well in pots and hanging baskets in bright filtered light. They need high humidity but hate soggy roots, so water only when dry.