There is not a one-size-fits-all answer to the best type of fertilizer for Rampion, since the right depends on the specific type of plant being grown, the environmental conditions, and most importantly the composition of the soil. However, as Rampion requires a lot of nitrogen, it is generally a safe bet to use high-nitrogen fertilizers. Manure or compost is the best choice for amending soil at the beginning of the growing season, and then feeding for the rest of the season can be done with a dry or liquid fertilizer. Feed lightly during the seedling stage, then steadily increase as the plant matures.
Many people find that vegetables grown with organic fertilizers have a superior taste to those grown with chemical fertilizers, but both will work. Some popular high-nitrogen organic options include fish emulsion, soil meal, compost tea, alfalfa meal, blood meal, and chicken manure.
When using chemical fertilizers, check the NPK number which indicates the relative proportion of the three macronutrients nitrogen, phosphorus, and potassium in the mixture. Since you want a high-nitrogen option, choose one where the first number is highest such as a 13-2-5, or even one that only contains nitrogen like a 16-0-0.