The least expensive way to do this is to use things like blood meal and fish meal for nitrogen, bone meal and bat guano for phosphorus, wood ash and kelp meal for potassium, dolomite lime for calcium and magnesium, and epsom salts as a source of magnesium and sulfur. Most of these items can be purchased cheaply at your local home and garden center and then mixed in small amounts into the soil before potting. Done correctly, you’ll only need to water your plants and occasionally add carbohydrates to feed the soil life. You want higher amounts of N through veg and less in flower gradually completely cutting it out by the end of the flower stretch (3 weeks). During Flower you want higher P AND K for bud development. Any questions feel free to ask. Hope this helps