Liquid plant manure

Liquid plant manures are fermented extracts of plant material that are used primarily as fertilizers, but also for pest control, plant strengthening and other phytosanitary purposes. The best known is nettle water, usually made from stinging nettles. Other well-known types are made from comfrey or horsetail.

Traditionally, it is prepared by open fermentation with daily stirring. However, Éric Petiot, author of a popular modern textbook on the subject, advocates eliminating any contact with oxygen.

Phytosanitary use
A literature review by the National Horticultural Society of France (SNHF) found references to phytosanitary use only for the late 1990s and onwards, and no scientific evidence of corresponding effects.

Political and regulatory situation
In 2017, the EU authorised the use of nettles (Urtica spp.) as a starting material for the production of commercial plant protection products.

In France, the introduction of new agricultural framework legislation in 2006 triggered a major controversy, the so-called "nettle manure war". The law banned the possession, marketing and advertising of unapproved plant protection products. Intended as a stricter legislation for conventional plant protection products and especially to better control banned products, this legislation also covered plant manures and other selfmade preparations that had never passed an official evaluation or approval process. It was widely seen as a lobbying success for agroindustry and a grotesque culmination of continued attacks on smallholder agriculture. A case involving agriculturist Éric Petiot, who was prosecuted by the General Directorate of Competition, Consumption and Repression of Frauds (DGCCRF) for co-authoring a popular book on plant manures, attracted public attention. The stinging nettle became the symbol of a movement and as a symbolic protest, activists demonstratively distributed the illegalized nettle water, for example at weekly markets. The Ministry of Agriculture lifted the ban in April 2011.

In Germany, the ingredients for certain liquid plant manures or the respective plant extracts are listed by the Federal Office of Consumer Protection and Food Safety as plant strengthening agents and are commercially available from several manufacturers.