Warriors of waste:
New guide to boosting vegetable production – with the help of the black soldier fly

Turning waste into fertilizer with the help of insects is a practical, sustainable way to grow vegetables. Now, a new farmer-friendly guide explains how producers in Africa can use black soldier fly frass – the nutrient-rich compost left behind by insect larvae – to increase vegetable yields, improve soils, and reduce the need for synthetic fertilizers.

Black Soldier Fly

Native to the Americas, the black soldier fly (Hermetia illucens) is now widespread in Asia, Africa, Europe and Oceania. Resembling a small wasp, its larvae have a voracious appetite, feeding on kitchen scraps, crop residues, manure, and other organic materials. As they eat, they produce frass – a dark mixture of droppings, leftover feed, and shed skins. Far from being waste, frass is a compost-like material rich in plant nutrients and beneficial microbes.

When integrated into vegetable production, black soldier fly frass can improve nutrient availability, enhance soil structure, and suppress soil-borne diseases, leading to higher crop yields and improved crop quality – all at relatively low cost. Research led by the World Vegetable Center (WorldVeg) in Ghana showed that frass application significantly improved tomato yields and postharvest quality.

The new training manual, Black soldier fly frass: A practical guide for vegetable production aims to equip farmers in Africa with everything they need to know – from establishing their own vegetable nurseries, to land preparation, optimal frass application rates, and safety precautions. It was produced by the World Vegetable Center (WorldVeg) and the International Institute of Tropical Agriculture (IITA), as part of a project funded by the Norwegian Agency for Development (Norad). The Guide is also available in French.

“Black soldier fly is fast becoming the not-so-secret weapon in the effort to improve soil fertility and promote sustainable agriculture amongst vegetable growers in Africa,” said Paul Alhassan Zaato, an agroecologist at WorldVeg and lead author of the new guide. “Its frass is a powerful gift from nature that farmers can harness and put to work to enhance vegetable production, improve their soils and reduce their reliance on chemical inputs. This guide shows them exactly what they need to do, from start to finish.”

Frass composting

FAST FACTS: Frass on the frontline

  • Frass is an excellent organic fertilizer for a wide variety of vegetable crops, including: leafy vegetables (amaranth, roselle, jute mallow, leafy pumpkin); root vegetables (carrots, beets, radishes); and fruit-bearing vegetables (tomatoes, peppers, okra, eggplant, among others).
  • Frass can be harvested after 9-23 days of composting, depending on the type of waste used. From 1,000kg of food and vegetable substrate, the process can yield approximately 250kg (25%) frass.
  • Frass contains beneficial microbes, including nitrifying and nitrogen-fixing bacteria that help make nitrogen available for plants. It also contains chitin (from larvae exoskeletons), which supports plant development and triggers plant defenses against pests and diseases.
  • Frass suppresses soil-borne pathogens such as plant-parasitic fungi and nematodes; it also makes mineral nutrients less accessible to pathogens.
  • Frass can help prevent infections from fungi like Rhizoctonia, Fusarium, and Pythium.

What happens next?

  • Training and dissemination – The new guide will be rolled out through farmer field schools, training sessions, and extension networks to ensure smallholder farmers can practically adopt frass use in vegetable production.

  • Cost Benefit Analysis: The next step will be to carry out a detailed cost–benefit analysis on the use of black soldier bly frass fertilizer

  • Policy engagement – Evidence from research and field use will be shared with policymakers to integrate black soldier fly frass into national soil fertility and sustainable agriculture strategies.

  • Private sector involvement – Entrepreneurs and agribusinesses will be encouraged to establish black soldier fly production units, creating jobs and ensuring a steady supply of frass for local vegetable producers.

 

Further research and monitoring – Continuous studies will track long-term soil health, crop productivity, and economic returns, while refining recommendations for optimal application rates and safety standards.

Frass ferilizer