Mealworms only output is their excrement – known as Castings or Frass – and it makes for fantastic fertilizer.

Studies have shown that mealworm castings work great on established plants.  It should be used very cautiously with seedlings.

Analysis of our Fertilizer has been completed by the University of Missouri Soil and Plant Testing Lab.

2.5-2-2.5 Fertilizer (NPK)*

  • Mix with water for indoor and outdoor fertilizing
  • Can be applied dry via a spreader for large areas
  • Minimal odor!
  • Dry and ready to use

How to Use:

  • Watering: Mix 1 cup fertilizer per gallon of water, let stand for 10 mins, water. Repeat every 2 weeks
  • Potting: Add 1 cup fertilizer per gallon of potting soil
  • Garden: Spread 1 pound fertilizer to every 20 square feet of topsoil


In general:

Insect castings naturally contain the nutrition plants require, beneficial micro-organisms, and the only immediately plant-available source of chitin (pronounced “Kite-in”). Chitin fortifies a plant from the inside out, causing an “auto-immune” response that signals a plant to produce natural toxins which fend off its natural enemies like pests and fungal pathogens. The EPA says that chitin and chitosan defend against botrytis (grey mold), powdery mildew, early and late blight, fungal pathogens in the root zone (root rot) and root-feeding nematodes.


Insect Castings for Row Crops & Raised Beds:
Add up to 1Lb. of insect castings per 20 sq. feet
Gently dig in to top 6 inches of soil and water thoroughly
Lightly top dress 2 times a month with castings and water thoroughly

Pre-Mix for Soil or Potted Plants:
Mix up to 1 cup insect castings per cubic foot soil or potting medium
Top dress or root drench 2 times a month
Apply castings weekly
For best results use dechlorinated or filtered water

Full-Strength Insect Castings Compost Tea Extract (root drench):
Add  1 cup of mealworm castings with one gallon of water
Wait 10 minutes, then water
Feed monthly or as desired
Use within 2 hours of mixing or refrigerate for up to 1 week
Do not store at room temperature once mixed


* this is an analysis from a single sample of our mealworm frass and represents an estimate of future frass nutrient contents. Always research your specific application, the above information is general and may not be appropriate for your plants needs. Midwest Mealworms is not responsible for any issues that arise as a result of usage of our frass. Our mealworms are fed a variety of wheat bran, potatoes, apples and carrots. We are not currently certified as organic.