This graph shows how different plants might fit into a ph scale. Anything below 7 is considered acid and above 7 considered alkaline. As a practical matter; if you buy a good soil mix it is pretty balanced and you don’t have to worry too much about PH. But if you add amendments to your soil keep in mind; they could change your PH drastically Example: Bat guano is very acidic and mushroom compost is on the alkaline side. If in doubt leave out.