The subject of soils, soil mixtures, and fertilizers has been made far too complex and mysterious. At the start, there are only a few things you need to know. You will learn by doing, and more easily than by reading, Soil has two functions to support plants and to nourish them and fertilizers or plant foods contribute to this second essential function.
In a greenhouse you soon discover how to vary the soil elements you supply the fine-rooted African-violets with a fairly light mixture, geraniums and amaryllis with something more substantial. You discover that pH isn't all that peculiar and that, anyway, most plants are amazingly accommodating to variations in soil "from acid to alkaline. Many different kinds of plants thrive on just about the same well-balanced soil mixture and on somewhat the same fertilizers. Soils are nothing to get alarmed about, but they are a fascinating study. As you come to know more about the culture of your favorite plants, you are also bound to find out a lot about soils. The soil that comes directly from your yard or garden does not necessarily contain the minerals and other elements that encourage growth in all types of plants in a greenhouse. So you may want to prepare a good growing mixture by making some additions.
But first, consider the structure of the soil you have.