PLANT FOOD AND NUTRIENTS - Cannabis Growing Guide. Plant foods have 3 main ingredients that will be the mainstay of the garden, Nitrogen, Phosphorus, and Potassium. These 3 ingredients are usually listed on the front label of the plant food in the order of N-P-K. A 20-20-20 plant food has a Nitrogen level of 20%. Secondary nutrients are Calcium, Sulphur and Magnesium.