Chillies are one of my favourite things to grow and some years we have had an entire glasshouse filled with 44 chilli plants of various sorts. This year I have been a bit more restrained with only 20 plants. These were raised in heated propagators, which we turned off a couple of weeks ago, but left the plants in place. This week they were in perfect condition for moving into their final pots. The plants were looking healthy and their pots were filled with fine roots but not yet pot bound.
I use fairly large pots of 10 litres per plant, filled with a fairly rich compost mix comprising, approximately: 3 parts multipurpose compost, 1 part loam / top soil, 2 parts horse manure, and a sprinkling of fish, blood, and bone. I have used this mixture for some years and have found that little or no supplementary feeding is needed, this mix has everything the plants need for robust, healthy growth through the entire season.
Chillies do not like wet compost. The mixture I use has a good balance of moisture retention and drainage. In heavier mixes, some grit might be useful. Chillies, once established, respond well if allowed to almost dry out before watering again. However, for convenience, we have these plants connected to an automatic watering system. This system is excellent and means that I can more or less forget about the plants now. I will inspect them from time to time for signs of pest damage, but generally we have little trouble with chillies.
This year we are growing four plants each of five varieties: the ubiquitous Cayenne, which has a useful heat for general culinary use; the Basque chilli Gorria; Serrano, a classic Mexican sort; Hungarian Hot Wax, which is good fresh, dried, or pickled; and Goat Horn. The latter is a new one for us this year. It is supposed to be much like a Cayenne pepper so it should be of good general use in the kitchen.