GROWING FROM SEED
Begonia seed is minute, so attention to detail is essential to ensure success. The seed tray must be prepared well in advance of actually sowing the seed. Ideally, three different grades of seed compost should be used, with a coarse layer in the bottom of the tray, followed by a medium layer and then by a fine layer on to which the seed will be sown. This is easily achieved by passing some of the compost through a fine riddle; the compost which fails to pass through goes in the bottom of the tray, compost which has not been riddled in the middle and the compost which passed through the riddle on the top. The compost should then be gently firmed before soaking by immersion (placing the seed tray in a tray of water). Any excess water should then be allowed to drain and the compost also allowed to warm through.
The seed is difficult to sow evenly, but this problem can be overcome by mixing it with silver sand. After the seed has been sown it must not be covered by compost but a sheet of glass should be placed on the top of the tray to maintain high moisture levels and humidity. The seed will give optimum germination at a constant temperature of 70 degrees Fahrenheit (21 degrees Centigrade) and therefore some sort of propagator is a must and results will be much better if it is thermostatically controlled. After placing the seed tray in the propagator a careful watch should be kept for germination and the sheet of glass wiped each day to prevent a build up of excess condensation. Full emergence takes between 14 and 21 days, after which the temperature can be decreased to 65 degrees Fahrenheit and the glass removed. The propagator will help keep the humidity high. Supplementary lighting is beneficial at this stage to keep seedlings in a vegetative stage. Ensure the compost does not dry out and a weak nitrogen liquid feed can be given to encourage rapid growth. Roughly five weeks after germination the seedlings are ready for pricking off, about one inch apart, into trays of seed compost.
This is a difficult operation and great care must be taken not to damage the tender young plants. The standard method to achieve this objective is to cut a small V in the pointed end of a plant label, which can then be used to lift the seedlings. A small nail can be used to make holes in the compost into which the seedlings can be placed. As soon as the seedlings are touching they will require a further move, this time (again using a seed compost) around two inches apart. In a further five weeks or so they will be potted into a three inch pot, this time into a potting compost and can then be moved onto the open staging.
If plants are required for greenhouse culture they can now be treated as plants grown from tubers. If they are to be bedded out, treatment is slightly different. Before planting takes place the site must be thoroughly prepared by incorporating some form of humus and a small amount of a balanced fertiliser such as Growmore. Ideally the site chosen should be shaded when the sun is strongest, but not so well shaded that plants become weak and spindly. The most essential factor in obtaining a first-class display is to harden plants off in a cold frame gradually exposing them to the elements. Begonias will not tolerate frost and this should be borne in mind when deciding when to plant out. After planting, each plant must be given a good soaking as this also lessens the chance of scorching taking place. It should also be noted that it will be two or three weeks before the roots will have grown sufficiently to enable the plant to obtain moisture from the soil and further watering will be necessary if a dry spell occurs.