Another difference is between organic and inorganic fertilizers. Plants take up nitrogen the same way from both types of fertilizers, but that doesn't mean all fertilizers can be simply boiled down to their NPK amounts. Fertilizers contain many variations of minerals. Some are only phosphorus, some are only potassium, some may be NPK with added micronutrients and so on. One size does not fit all.
Fertilizers are important ingredients in plant health management.
Whether it is for maximizing plant growth in nurseries and gardens or maintaining plant health in soils deficient in needed nutrients, fertilizers are important pieces of the plant health puzzle. Teach your customers about how fertilizers fit with the overall practices of proper plant selection, proper planting practices, good maintenance and pest control management. And don't forget to keep up to date yourself. Learn from your green industry peers and frequently consult trade publications, books and the Internet.