There is a soil type known as "living soil", withthe idea behind it to allow the microorganisms in the soil to break down the compounds in the soil and makinhg it available to the plants as it grows. Most pre made fortified soils only last for about 3-4 months, while the living soil keeps providing nutrients until the food is consumed. I use
Promix and only add water and water soluble fertilizer every few weeks... it not an easy task although it can and is done by some growers on the site here. Look up the living soil thread and I'm sure you will get additional help from others.