Methods to convert the light and powdery mealworm castings into a suitable fertilizer product are disclosed. The methods can include saturating the mealworm castings using an infusion process with a liquid such as water until an elevated temperature is reached. The mealworm castings can be replenished and the infusion process can be repeated until the targeted N-P-K rating is achieved. The saturated mealworm castings or mealworm cake can be dried and formed into fertilizer pellets or into a granular soil-like product. In some examples, a binding agent such as dried mashed potato extract can be added to the saturated mealworm castings. In some examples, the fertilizer excludes artificially produced chemicals, hormones, antibiotics, and steroids. In some examples, the fertilizer has an N-P-K rating of 4-3-2. In some examples, the mealworm castings are produced by mealworms fed wheat bran and raw carrots.