Those of us who live in cold / temperate climates have to plan the sowing of their flower and vegetable seeds very carefully. I live in the UK, where our outdoor "growing season" is quite short - let's say 6 months of the year. If you sow seeds outdoors when the weather is not right they will not do well - they may never even germinate, and if they do they will be struggling to survive from Day 1. This means that we need to start off many of our plants indoors. This is easier said than done! If you are lucky enough to have a conservatory or a heated greenhouse you'll be OK, but for many people (like me...) the only option available is a windowsill - preferably above a central heating radiator. The trouble with this is that most windowsills only get a limited amount of direct sunlight, and seedlings really need lots of light, so you may find yourself shifting trays of seeds from one side of the house to another twice a day!
Anyway, for better or for worse, this is my approach to indoor seed-sowing:-
Make sure you are sowing seeds at the right time. Look at the instructions on the packet, and follow them as closely as possible. Many plants (especially vegetables) come in lots of different varieties, some of which are suitable for early sowing, some for late sowing, so choose the right ones.
Don't start too early. I know you'll probably be impatient and will want to get things going as soon as possible, but it really is better to wait until conditions are suitable. For instance, sowing seeds in January in the UK is seldom a good idea, because even if you can provide enough warmth, the days are very short and you may not be able to provide enough light. You might therefore decide that it's worth providing some additional light artificially.
Ready-made Propagators, with or without in-built heating and/or lighting are available everywhere (just put "Propagator" into your Web Browser and you'll see what I mean), but these things can cost a lot of money - maybe more than you want to spend. You can get decent results with something very simple though. I use these:-
They are basically a seed-tray with a removable clear acrylic cover. In fact you can buy trays and covers separately if you want. The cover has adjustable sliding vents in the top to assist with providing the right conditions. These things fit quite conveniently on any widowsill; they are lightweight and easily portable, so you can take them outside when conditions allow; and they are inexpensive. Furthermore, when you are not using them they are stackable so that they take up much less space.
This is my technique: fill the tray part of the propagator with compost, preferably "Seed and Cutting Compost" which is specially formulated for this role; "General Purpose" potting compost will do at a pinch, though you may have to sift it through a "riddle" (coarse garden sieve); level it off and water it with warm water. Don't soak the compost too much, it just needs to be moist not wet.
Depending on the size of the seeds you are using, either sprinkle them (thinly!) on the surface of the compost or place them individually in position, adjusting as necessary using a dibber (see photo below). With bigger seeds it's a good idea to push them into the surface of the compost so that they are at least half covered by it.
Then cover the seeds with a layer of dry compost. The thickness of this depends on the size of the seeds. The dry compost should cover the seeds, however big they are. I sieve this top layer of compost using an old kitchen sieve. This means that the emerging seedlings are not hampered by large lumps of compost. Don't water the compost again at this stage.
|Sieve and Dibber|
Now put your seed-tray somewhere warm (such as in the airing-cupboard or on top of the fridge) for a few days, until the seeds germinate. If you have covers like the ones I have shown, use them, but if you haven't a clear polythene bag will serve the same purpose - which is to provide a warm humid atmosphere. The optimum temperatures for germination of your seeds will be shown on the packet, but I have to say that I find most vegetable seeds to be very tolerant. If they don't get the ideal temperature it may take longer for them to germinate, but it usually doesn't stop them germinating.[Of course this is not always the case.]
Most seeds benefit from the exclusion of light during germination (check what the seed packet says). So if your trays are in a light place, cover them with some sheets of newspaper. Make sure that you check the trays frequently (a couple of times a day after the first few days), and as soon as the seedlings emerge, put them somewhere that gets as much light as possible. If the seedlings do not get enough light they will go "leggy" - in other words long and spindly, like these:-
What you are looking for is short, sturdy seedlings like these for instance:
|Lettuce seedlings - 4 different types in one tray|
Try to keep the seedlings at a fairly constant temperature, and away from draughts from this point onwards. They don't generally like big fluctuations. This may for instance entail moving your seeds off the windowsills on frosty nights. Whenever conditions allow (that's to say when it's sunny and warm), I often take my propagators outside and put them on our garden table so that they can soak up a bit more light.
Some people think that fanning the seedlings for a few minutes a day on a regular basis (either with an electric fan, or by hand) is beneficial. This mimics the wind conditions that the seedlings would experience if they were growing out in the open air. Personally, I have never done this, but I think it is probably true: just as in humans, seedlings that get plenty of exercise ought to grow up into healthier adults!
Once the seedlings begin to grow, check the compost frequently and water it as necessary. Again, don't be too enthusiastic here: keep the compost on the dry side of moist. Wet compost is likely to promote fungal diseases, often referred to as "Damping Off", which usually proves fatal to small seedlings.
You can see from my photos that I often sow seeds in small pots and keep those in the propagators. This is a good way of using one propagator to raise small quantities of several different seedlings, which will probably grow at different rates. When the seedlings in one pot get too tall to fit under the cover any more, you can remove it separately. If you use this approach, don't forget to label the individual pots so that you remember which is which!
You may find that you have sown your seeds too thickly. If they are overcrowded they will not grow well, so it is best to thin them out soon after germination . If the seedlings are very small, I suggest using a pair of tweezers for this task:
When your seedlings have developed their first set of true leaves (not the cotyledons, or "seed-leaves") it is time for pricking them out. This simply means transferring them to individual pots. It's a task that needs to be done gently, to avoid damaging the seedlings' delicate roots, which may already be quite long by this stage. These "thinnings" are too young for transplanting, but the photo shows how big the roots are.
Half an hour or so in advance, wet the compost thoroughly - yes, WET this time, not moist. This will loosen the seedlings and make them easier to separate. At the same time, fill some small (3"?) pots with compost and water them too. Then, when you're ready, ease each seedling out of the tray with a suitable implement (such as the plastic dibber pictured above, or simply a small piece of wood), hold it by a leaf, not the very delicate stem, and transfer it to its new home - a generously-sized hole made with your dibber in the compost in the new pot. If the seedling doesn't easily fit into the hole, don't try to force it - just enlarge the hole. Plant the seedling quite deeply in the pot, and firm the compost in around it. Then put the potted-up seedlings somewhere cool and out of direct sunlight for a few hours to recover.
|Celeriac seedlings shortly after "pricking-out"|
Note: the best way of raising of seeds is a subject much debated by gardeners the world over. Every one has their own way of doing it. What I have written about is my way, and in no sense is it intended to be seen as the right or only way!