Frass - Darkling (Tenebrio molitor)

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Size: 1 lb
Sale price$29.99 Regular price$49.99


Frass, the excrement of darkling beetles (Tenebrio molitor), is rich in nutrients and can be used in various ways to benefit your garden or indoor plants.

  • When first added to soil, it quickly provides nitrogen, phosphorus, and potassium to plants, and slowly continues to releases these three elements over time.
  • Frass nourishes chitin-feeding bacteria and fungi, which in turn devour gnat eggs and root-feeding nematodes.
  • It provides chitin and enzymes which increase plants resistance to pests.
  • Frass fortifies plants’ cell walls and stimulates plant immune system
  • Shown to increase plant yields (Kagata, H. et al, 2012)
  • Shown to be as effective as NPK fertilizers but also improves soil quality and prevents nutrient runoff (Houben, D. et al, 2020)


  • Top dress with 1 cup per gallon of soil.
  • Brew 2 tbsp per gallon of water for use in hydroponics foliar spray or liquid fertilizer.
  • Add to compost piles to improve decomposition rates.

Here's how you can use frass for plants:

  1. Soil Amendment: Frass can be added directly to the soil as a natural fertilizer and soil conditioner. It improves soil structure, aeration, and water retention while providing essential nutrients to plants. Mix it into the top few inches of soil or use it as a side dressing around established plants.

  2. Compost Booster: Incorporate frass into your compost pile or bin to accelerate decomposition and enrich the resulting compost. The nutrients in frass can help balance the carbon-to-nitrogen ratio in your compost, leading to a nutrient-rich compost that can be used to fertilize plants.

  3. Seed Starting Mix: Create a seed starting mix by mixing frass with other components like peat moss, vermiculite, and perlite. This mixture provides young seedlings with a nutrient-rich environment that encourages healthy root development and early growth.

  4. Liquid Fertilizer: You can make a liquid fertilizer by steeping frass in water. Add a few tablespoons of frass to a gallon of water and let it sit for a few days, stirring occasionally. Then, strain the liquid and use it to water your plants. This provides a quick nutrient boost to your plants.

  5. Foliar Spray: Dilute frass in water (around 1-2 tablespoons per gallon) and use it as a foliar spray. Spraying frass solution on the leaves of your plants can enhance their nutrient uptake through the foliage.

  6. Pest Deterrent: Frass may also have some pest-repelling properties, helping to deter certain insects and pests from your plants. However, this effect can vary depending on the source of the frass and the specific pests you're dealing with.

Info Sources:

Kagata, H., Ohgushi, T. Positive and negative impacts of insect frass quality on soil nitrogen availability and plant growth. Popul Ecol 54, 75–82 (2012).

Houben, D., Daoulas, G., Faucon, MP. et al. Potential use of mealworm frass as a fertilizer: Impact on crop growth and soil properties. Sci Rep 10, 4659 (2020).

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