Onions require a high source of nitrogen. A nitrogen-based fertilizer (ammonium sulfate or ammonium nitrate) should be applied at the rate of one cup per twenty feet of row. The first application should be about three weeks after planting and then continue with applications every 2 to 3 weeks.
Capsicums grow well in containers of at least 25 cm depth of soil. Capsicums are slow to develop fruit and can take up to 3 months depending on the variety chosen and your climate. All capsicums are green to start with before developing their full colour eg red, yellow, orange or purple. They can be picked early when green but the longer you wait the sweeter they will be.
Different approaches to fertilizing can be used to produce a high quality crop of any species. Often despite major differences in fertilizer programs between two growers excellent results are achieved when the two crops finish. In this piece basic fertilizer programs are recommended for the most important crops currently grown in East African greenhouses. An individual grower may need to "fine-tune" these recommendations to fit his/her conditions.