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Fermented plant extract (purin)

A fermented plant maceration, used mainly as a liquid fertiliser.

Watch the videoLe purin d'ortie fait maisonGrandifloraSee the nettle entry

Explanation

The plants are fermented in water for 1 to 3 weeks, then strained and diluted. They are credited with fertilising and repellent virtues that French trials barely confirm: against aphids, slugs and flea beetles, at best a slight delay in aphid infestation, soon erased by natural enemies (SNHF, 2012). An old European peasant tradition, codified in the 20th century by Eric Petiot and Bernard Bertrand (Éditions de Terran).

Refined definition

The purin (sometimes called a “fermented plant extract”) is obtained by anaerobic maceration of plants in rainwater for 1 to 3 weeks (depending on the plant and temperature). Fermentation breaks down the plant structures and releases the minerals, vitamins and active compounds. It is strained and diluted 1:10 or 1:20 for spraying or watering. To be distinguished from a decoction (brief cooking), a maceration (cold, without fermentation) and an infusion (boiling water poured over the plants).

Key points

  • Three great classics

    Nettle purin: traditionally used to boost leafy growth; analysed on its own, however, it contains little available nitrogen, and French trials showed no clear effect either as a fertiliser or against vegetable diseases (SNHF, 2012). Dilution 1:10 for watering, 1:20 for spraying. Comfrey purin: rich in potassium, traditionally used to support flowering and fruiting. Dilution 1:10. Horsetail purin (Equisetum arvense): rich in silica, used preventively against blight and powdery mildew; in France, trials found some effect only on grapevine, combined with copper, and none on the vegetable diseases tested (SNHF, 2012). Dilution 1:5 for spraying. Sources: Eric Petiot, Purins d'ortie et compagnie, Éditions de Terran, 2007; Bernard Bertrand, Purins d'ortie & compagnie, 2003.

  • Purin or compost?

    Don't confuse the two: purin is used as a liquid FERTILISER, a boost given to the plant (nettle traditionally for foliage, comfrey for flowers and fruit), even though French trials find very little available nitrogen in it and no clear effect (SNHF, 2012); compost is a SOIL AMENDMENT that feeds and improves the soil over time (structure, humus, soil life). One is meant as a quick boost, the other builds long-term fertility. Sources: Dominique Soltner, Les bases de la production végétale; Bertrand, Collaert & Petiot, Purin d'ortie & Cie (Éditions de Terran).

  • Preparation method

    1 kg of fresh plant per 10 L of rainwater (not tap water: chlorine inhibits fermentation). A plastic or wooden container, never metal. Cover but not airtight (gas). Stir every 2 days. End of fermentation: when the smell turns foul and there are no more bubbles at the surface (8-15 days depending on temperature). Strain and keep away from light, in stoppered bottles, keeps for 1 year.

  • Regulatory status in France

    Nettle purin was the subject of a controversy in 2006 (the DGCCRF had threatened to ban its sale). Today: personal, non-commercial use is free. For sale, use as a “natural preparation of low concern” (PNPP) is regulated by the order of 27 April 2016. More than 30 PNPPs are authorised, including nettle, comfrey and horsetail extracts.

Watch out for

  • • Horsetail purin is used preventively, never on a declared attack, and its effect on vegetable diseases has not been confirmed in trials (SNHF, 2012).
  • • NEVER use purin at high dose on young plants or fragile crops: risk of leaf burn. Always dilute.
  • • Very strong smell, prepare it away from dwellings. Some local authorities forbid making it in shared gardens for this reason.

Examples

  • • Nettle purin (traditional use: leafy growth)
  • • Comfrey purin (potassium, traditional use: fruit and flowers)
  • • Horsetail purin (silica, preventive use, effect not confirmed in the vegetable garden)
  • • Fern purin (traditional use against pests, effectiveness not confirmed in trials)
  • • Tansy purin (traditional use, to be used in moderation: contains thujones)

Sources

  • SNHF, Conseil scientifique (2012). Protection des plantes, tradition et macération d'ortie. Société nationale d'horticulture de France (jardiner-autrement.fr).
  • Bertrand, B., Collaert, J.-P. & Petiot, É. Purin d'ortie et compagnie : les plantes au secours des plantes. Éditions de Terran.
  • Soltner, D. (2000). Les bases de la production végétale, tome 1 : le sol et son amélioration. Sciences et techniques agricoles.