Advice is given throughout on sowing seeds needing artificial heat for successful germination. However, there are a number of aspects of this fascinating branch of plant propagation best summarised here.The first point to make is you shouldn't buy seeds of such plants until you are confident you have the facilities to raise them successfully. But this doesn't necessarily mean you have to invest in costly equipment.
All seeds need water, oxygen, the correct amount of light and the right level of warmth to germinate. Supplying that warmth could be a simple matter of giving the sown seed a place above the central-heating boiler, a temporary home in the airing cupboard or a sunny windowsill.
The pleasure of raising one's own bedding plants is infectious and one soon realises that something a little more spacious and controllable can be had for very little cost. That something could be an electrically heated propagator capable of accommodating two or more standard size seed trays, using no more power than a 100-watt light bulb but thermostatically controlled to give the precise temperature for successful germination.
Of course, remember a tray of seedlings is the starting point. Pricking out the seedlings (Pricking Out) follows and will involve accommodating several more trays or many more pots right through to the hardening off stage. You will appreciate enthusiasm for this rewarding hobby can soon take the gardener from a small propagator to the hankering for a greenhouse.
However large one's ambition, one should never forget quite small safeguards are necessary and top of the list is cleanliness. Trays and pots should be sterilised before use. So too should the cover of the propagator or glass of the greenhouse. Fresh compost should be used at the start of the season and emerging seedlings should be treated with Cheshunt Compound to prevent damping off.
Some seeds remain viable for a year or more after the packet seal has been broken, but it is advisable to carry out a germination test before the correct sowing time. Saved seeds require precisely controlled conditions to maintain a reasonable germination rate. The major seed companies, of which Thompson & Morgan is one of the longest established, have become popular because they provide high quality seed of guaranteed viability. It is often a false economy to save small amounts of seed from one year to the next.
Most seeds germinate best if the tray is covered with a sheet of glass or plastic to retain the moisture in the compost. Some require dark to germinate and this can be provided by keeping the tray in a light, warm position while it is covered with a sheet of newspaper.
A daytime temperature of 65-75F (18-24C) is suitable for most undercover seeds and a drop at night to about 55F (12.5C) is permissible. When the seedlings have emerged, however, the daytime temperature should be lowered to about 65F (18F) and the seedlings given a light position which is away from direct sunlight.
As with many other aspects of life, preparation is an important factor in successful seed raising. For seeds that can be sown directly into the soil, preparation involves ensuring the site is in a suitable condition. The soil should be free of weeds, large stones and debris and be broken down as finely as possible to what's called a fine tilth. This is achieved by forking over the top few inches of soil, then raking it to as crumbly a texture as possible.For many vegetables, some hardy annuals and tree seeds a special seed bed is prepared in an open but sheltered position. The seed is sown thinly in drills made to the recommended sowing depth for that particular variety. To make the drill you can use the reverse side of the rake head to make a V-shaped drill following a taut garden line.
Alternatively, you can lay the rake, teeth uppermost, along the garden line and gently press the handle into the soil to make a U-shaped drill.
The important thing is that the seed should be in good contact with the soil. In dry conditions it is advisable to moisten the drill thoroughly before sowing, and some gardeners believe that lining the drill with moist peat is an aid to even germination.
After sowing the seed, rake soil over the drill or cover with peat and firm it with the flat face of the rake. The final touch is to mark the drill with a plant label giving the type of seed variety and date sown.
Annual flower seeds can, or course, be sown directly into those parts of the garden where they will flower.
For best results choose sunny areas that are well drained. At sowing time the soil should be moist and at a minimum temperature of 50F (10C). Annuals don't need a nutrient-rich soil, so dressings of artificial fertiliser aren't necessary. All soils and plants benefit, however, from organic matter that has been dug in to the top few inches of the soil early in the year.
The most effective technique when sowing a range of annuals is to sow the seed in patches, rather than in regimental lines.
It's helpful to draw a plan of your intentions, placing the various varieties according to their height, spread and colour scheme you are aiming for.
Prepare the soil as described above, then mark out the groups with a trickle of silver sand or flour. Sow the seed by sprinkling it as evenly as possible. One way of doing this is to put the seed into a triangular wedge of paper, hold in one hand while tapping it with the fore-finger of the other hand.
Annuals need only a light covering of soil which can either be sieved over the seed or the soil can be raked gently after sowing then firmed with the flat face of the rake.
When the seed has germinated it will be necessary to thin out any seedlings that are overcrowded. Do this as soon as possible after emergence, but a further thinning out might be needed when the plants have developed several pairs of true leaves.
Remember that in the early life of the seedlings adequate space is a key factor in determining the plants' subsequent development, so weeds must also be kept under control.
Detailed advice on sowing vegetable seeds is given on separate pages (see our Vegetable Seed Sowing Guide).