Tuberous begonias have beautiful rose like flowers in a wide variety of colours and forms. Flowers may be single or double, plain, ruffled or toothed. They bloom throughout the summer, thriving in shady spots where few other plants with long bloom periods and showy flowers can grow. They can also be grown in pots on patios, in hanging baskets and indoors.
Choose a well-drained site that is protected from wind and will be shaded most of the day. Early morning and late afternoon sun will not harm them. The hotter your growing region, the more shade they prefer. Plant the tubers by with the soil just barely covering them. Plant 20-30cm apart with the indented side facing up.
After planting water generously to settle the soil around the tubers. Roots and sprouts will form in a few weeks, depending on soils and air temperature. Keep watered enough to keep the soil very slightly damp but never enough for it to be soggy. Try to water the soil around the plants rather than the plants themselves, to avoid mildew. At the first sign of a white patch on any of the leaves apply a fungicide right away. Feed Begonias with a well-balanced plant food every 2 to 3 weeks.
Stake stems as required. Take care not to damage the tuber. Male and female flowers appear separately on the same plant. You can pinch off the smaller female side buds for larger male flowers. Pinching off the first 3 or 4 buds of the season from each plant will encourage larger flowers
After flowering has finished for the season leave the foliage in place, don't cut it off. The leaves will gather sunlight, create food through photosynthesis and strengthen the bulb for the future. Water as needed. Leaves and stalks may be removed when they yellow. (If you live in an area where your begonias aren't winter hardy, dig the tubers before the first frost, dry for a few days and then store in a cool place in paper bags or cardboard boxes filled with peat moss.
Fill your containers with good quality, well-drained potting mix. Make sure there are adequate drainage holes; begonia tubers must never sit in waterlogged soil or they will rot. Self-watering pots are ideal. Keep in mind the mature size of the varieties you have chosen and plan your container sizes accordingly. Barely cover the tubers with potting mix. Water sparingly and increase water as the plant develops leaves. Avoid watering foliage if possible. Try to keep the plant continually moist.
Place pots in bright, indirect light indoors or out. Early morning or late afternoon sun is acceptable outside. Fresh air is essential as flowers will drip in stuffy conditions. The hotter your growing region, the more shade they prefer. Apply a combination fungicide and insecticide spray every week from the time that leaves are 15cms long. Stake stems as required. Take care not to damage the tuber.
Stop watering from about mid April. As long as water is applied the plants will continue to grow and flower but become unduly tall and leggy and need much extra staking. Lie the pots on their sides and after several weeks remove the detached top growth. Removed tubers and store them in a dry place.
At the end of August put the tubers out to sprout, concave side up in bright, indirect light then start all over again.