Once your pepper-seeds have successfully germinated and you’ve got your seedlings, you now need to give each of your baby plants their own little space to grow, and also supply them with what they need most at this point: light.
So let’s sort out the space aspect first. If more than one seed per starter pot or jiffy pellet has germinated, you ought to seperate the seedlings and put each of them into their own little pot. Otherwise the roots will entangle and it will be impossible to separate them later without doing damage to the plants and their root-system. So carefully put the pot upside down or break up the pellet in order to get the seedlings out. When you handle the seedlings, always hold them by the leaves and the stem, never by the roots which are very delicate and vital. A seedling might survive the loss of a leaf, but root-damage is likely to kill it off.
Plant the separated seedlings into starter pots with starter soil. Moisten the soil thoroughly by using a spray-bottle, and then bury the seedling deep enough so the first pair of leaves is about one centimeter above the soil-line. Pot-size and soil-quality do matter. I use pots with an edge length of about three inches and quality starter soil. Using bigger pots would make it harder for the plant to form a proper root-ball, and as a consequence it will show slower overall growth in later stages. The starter soil is an off-the-shelf soil-mix specially designed for seedlings – it hasn’t been pre-fertilised and it’s got a loose consistency thanks to the portion of Perlite in it. This facilitates permeating the soil for the roots, and the absence of fertiliser prevents the seedling from burning by overfeeding.
Once you’ve moved each of the seedlings into their own little homes, it’s now absolutely vital to supply them with the right kind of light in abundance. Over here in Berlin, there isn’t enough natural light for pepper seedlings to grow before late March/early April, and the season is pretty much over in October already. With insufficient light, the plants will become leggy and thin, rather than stout and sturdy as they should be. So if you live somewhere around the same latitude as myself, you need to start out early and give the seedlings some artificial light for the first couple of weeks.
I’ve built a very simple and inexpensive (< 20 Euros) grow-box for that purpose. It’s basically a big cardboard moving-box lined with aluminium foil along the walls and laid out with styrofoam on the floor. I’ve fitted it with two 18 Watts fluorescent tubes hooked up to a timer that keeps them going for 14 hours a day.
Note that the type of light, or rather its colour temperature is very important here. In nature, the colour-spectrum of natural light keeps changing throughout the year, and plants use it as a clock that tells them when it’s time to grow foliage and when it’s time to produce fruit. So if the seedlings get the wrong type of light now, they might be sent into flowering mode when really they should be putting all their energy into vegetative growth. Ideally the colour temperature of the lights should be at 6,500 Kelvin which resembles the spectrum of natural light on a bright and slightly clouded summer day. The kind of tubes that supply it are marked with the number “865” on the packaging as an international standard, as for example “Osram Lumilux Cool Daylight” (which I use).
The plants will stay in the grow-box for about six weeks, and during that time there isn’t really much more to do than to keep the soil a wee bit moist (but not wet). In late March they will move on into 1.5 liter pots on a bright window-sill.