Growing Begonias in the Greenhouse
The tuberous-rooted double begonias are among the most colourful of the family, with bold flowers in vivid shades of yellow, orange and scarlet.
For indoor use, the tubers should be started into growth in February or March in a temperature of not less than 10°C. At the same time, care must be taken not to let the temperature go above 18°C., and it should be kept as even as possible to ensure steady growth without checks.
Trays or shallow boxes should be filled with a mixture of one part each of good sweetand , with a half part of coarse silver sand. See that these are well mixed and moist without being wet. The tubers should then be firmly set in the boxes with their rounded surface downwards, for it is from the dented surface that the new shoots appear. Do not place them too closely, otherwise the fibrous roots will become matted together and broken when the tubers are later transferred to pots. Leave the crowns of the tubers exposed to discourage any tendency to rotting.
The best growth is produced in a humid atmosphere. As soon as the shoots are an inch high, the tubers should be potted up singly in a mixture of well broken-downor fibrous loam, leafmould or , a little silver sand and, wherever possible some old cow manure. Failing this, well-decayed stable manure or bonemeal should be included.
For the first potting, use the 3-½-in. size, except in the case of older tubers, which may be large and therefore need a 5-in. pot. If the potting mixture is brought into the shed orthe day before use, it will be warmer and therefore will not check the growing tubers so much. Loosen and lift the tubers from the box with great care, so as not to damage the roots, especially the tips. Then, having put some crocks at the bottom of the pot and half filled it with soil, place a tuber on the surface and gently fill in and firm the soil around it, finishing off so that the top of the tuber can just be seen.
Do not subject the newly potted plants to strong light for a few days, but afterwards give plenty of light and air, watering as necessary. It is always wise to avoid watering begonias when the full sun falls on the foliage, for this may lead to spotting.
For outdoor cultivation, the tubers need not be boxed until April. The growing plants are subsequently hardened off before being bedded out. Planting out of doors should not be attempted before the end of May or early June when all danger of frost is past; if the soil is fairly moist then growth will be rapid and flowers will soon appear.
After flowering the tubers should be removed from pots or beds when the foliage has died down, carefully cleaned and stored in a dry, frostproof place until the next planting time. It is wise to examine them occasionally during the winter, and remove any damaged or decayed specimens before they spread disease.
There is a separate group of foliage begonias and these are the cane types. These are far larger and have a fairlyhabit, shooting up tall canes clothed in spotted and sometimes plain leaves. The leaves of the plants in this group are generally less impressive than those bred from Begonia rex, but the plants do have a certain grace.
They need the support of a frame to climb up as the canes do not support themselves well. They should be regularly pruned back as the old stems lose their leaves and the plants can often start to look leggy and straggly as they age. Cut old canes right back to the base of the plant. This group can take more water than the smaller begonias and should be watered right through until late winter, when they should be allowed to rest until starting watering again in mid-spring.