After filling, trays and pots should be watered well. The best way to do this is from the bottom so stand them in about an inch of tap water and leave them until the surface is wet. Then remove them and allow to drain for at least half an hour.
Now sow the seeds thinly and evenly over the surface. Larger seeds can be sown one per cell in plug trays, cell inserts etc. or in individual small pots. If they are not sown thinly the resulting seedlings will be overcrowded and will grow poorly due to being in competition with each other. They will also be more difficult to transplant and more prone to disease problems. Large seeds can easily be positioned with the fingers but small ones are more of a challenge and various seed sowing devices are now on the market to assist with this task. In the absence of such a device, the end of a damp matchstick can be used to pick up and position individual seeds. Alternatively, a simple but very effective aid to scattering small seeds in a controlled fashion can be made by folding a stiff sheet of paper to form a groove. The seeds are tipped into this groove and the paper is then inclined and tapped gently and repeatedly to dispense the seed. Even when using such a sowing aid, it is easier to sow and see where you have sown very small seeds if they are first mixed with a carrier such as fine dry sand.
As soon as the seeds have been distributed on the compost, very fine ones should be pressed gently into the surface but otherwise left exposed. Seeds which require light should be treated similarly or (larger ones) can be covered with a thin layer of seed sowing grade vermiculite which lets light through. For all other seeds follow the instructions on the seed packet but a good rule of thumb is to cover to a depth which is about three times their diameter. Use a fine sieve, such as a flour sieve, to cover small to medium seeds with an appropriate thin layer of compost. Alternatively, fine vermiculite can again be used and we recommend it as it holds more moisture than compost yet, at the same time, is very well aerated. It is also sterile and won’t form a layer that might be lifted by the germinating seedlings. Only very large seeds such as beans, marrows and nasturtiums require some alteration to these methods and we have found that, rather than being covered after sowing, they are best inserted into individual small holes of the appropriate depth.
If you don’t have a propagator, the germination of smaller seeds sown at or near the surface will be assisted if the tray or pot is now covered with clingfilm or a sheet of glass or plastic. This reduces evaporation and so lessens the chances of the seeds drying out. Simple plastic propagator lids which are very cheap and fit over a standard seed tray are an alternative to the above and one we can thoroughly recommend.
Now place your pots or seed trays in a place where a suitable temperature can be maintained. Most seeds require a daytime temperature of 18-24ºC (65-75ºF) to germinate successfully. This can fall a little at night but basically warm conditions must be maintained at all times. Where this cannot be guaranteed we strongly recommend the purchase of a heated propagator although the sowing of some seeds can be delayed until nights are less cold. Seeds being germinated on a windowsill should be moved to a warmer location overnight, particularly if the curtains are drawn. Those types, such as greenhouse cucumbers and pelargoniums that require particularly high temperatures can be germinated in the bottom of an airing cupboard but must be removed as soon as the first shoots start to appear. If there is any doubt about the night time temperature at the location chosen for the germination of your seeds, this can easily be checked using a maximum-minimum thermometer.
For seeds which need light as well as warmth, place the containers in a well lit place but out of direct sunlight. For other seeds, particularly small seeds sown on the surface, a dark place is preferable or they can be covered with newspaper to exclude most light until they germinate. Be careful not to leave propagators or covered seed trays in a place where they can receive too much sun or be subject to excessive daytime temperatures, e.g. on a sunny windowsill or in an unshaded greenhouse. This becomes more important as the days lengthen and the sun becomes stronger.Next page