The invention relates to a method for treating extinguisher powder wastes with the aim of recycling the waste into agricultural fertilizers. The invention includes mixing the extinguisher powder wastes with a viscous cohesive agent, and blending a drying agent into the obtained mixture. The cohesive agent is based on sugar by-products, more particularly being vinasse or molasses. The drying agent is notably based on crushed and dried vegetables and, more particularly, on fruit pulp, for example, grape pulp.