It is getting a little late to plant chilli seeds now, in the northern hemisphere anyway,(although there are still a few you can get away with). But there is still time to dwell on why your seeds didn’t grow, and time to learn some lessons, so here are a few reasons why your’s may not have done well.
1/ Poor quality seed. Seed that has been stored in damp or warm conditions isn’t going to germinate well, also the older seeds get the less viable they become. I still germinate seeds after a couple of years, but after 3 year or more they really don’t do well unless you have stored them in laboratory conditions of controlled temperature and humidity.
It may be you to blame, or it may be the seed seller. Reputable seed sellers should ‘germ test’ each batch of seeds before they are packaged, this involves germinating a few of them each time and working out the germination rate. If it isn’t up around 90% they should either not sell them, or at least warn you of the problem and give you extra ones to plant.
2/ Too dry – If your seeds are allowed to dry out after you have planted them, it is likely they won’t survive. Keep the compost moist, but not too wet. If you think you could grab a fist full of it and squeeze water out then it is probably too much.
3/ Too cold – They won’t germinate at all if they spend too long below about 18°c. You will only get the best germination rates if you keep them constantly above room temperature.
4/ Too hot – A heated propagator, in direct sunlight, where the temperature might reach 50°c is going to kill of newly germinated seeds before they see the light of day, either by inhibiting germination, or baking them dry. Always try and keep your seeds warm, but don’t overdo it.
5/ Damping off – Strictly speaking this isn’t a reason for non germination, it is an affliction of seedlings, not seeds, but it is one reason why germinated shoots never make it to the surface. Damping off is simply a term used to describe rotting, when bacteria in the soil thrive because of wet conditions and lack of airflow. Think of where mould grows and you will get the idea. Usually it happens to crowded seedlings emerging from soil that is contaminated with bacteria and mould spores but it can happen to seedlings before they emerge from the soil. To guard against it, use clean new compost, not stuff that has sat in a damp shed all winter. Don’t water-log it, and don’t plant the seeds too deep, 1cm is more than enough. I generally use vermiculite to cover seeds, it is sterile and holds a little moisture but drains well.
For something more on germination times have a look at this earlier blog entry.