What do you mean don’t feed in soil? Pretty much every farmer in the world grows in dirt with fertilizer.
FFOF is primarily peat moss and wood chips (which actually bind up nitrogen and why it’s “aged”), that help soil
hold nutrients and improve aeration and drainage, but has little or no nutrient value at all. FF does have some added nutrients (earthworm castings, bat guano, fish emulsion, and crab meal) - enough nutrients to last a few weeks (maybe a month at most), after which a cannabis plant will develop seriously deficiencies if you don’t add fertilizers. FF specifically says “Use
FoxFarm Fertilizers & Liquid Plant Food concentrates in conjunction with our soil mixes.”