Kaolin, Zeolite, Bentonite: Rock flours

Stone flours are widely used in agriculture especially in organic farming, where they are a valid alternative to fungicides and insecticides for the garden and orchard.

These flours or powders are finely machined minerals function as a kind of mechanical obstacle to the harmful action of certain pests, without causing negative side effects on the environment and for this reason they can be used for natural cultivation.

Let’s see what are the most common rock flours for agricultural use , how to choose them and what are the best ways to use them make the most of the orchard and the organic garden. In particular, we focus on kaolin zeolite and bentonite which are the three most commonly used mineral powders that may be most helpful.

Contents [Ocultar]

  • Kaolin

  • Zeolite

  • Bentonite

  • The use of rock dust in organic farming


Kaolin is a mineral of sedimentary origin which disperses easily in water. It is composed mainly of aluminum and silicon and comes in the form of a chemically inert white powder.

Watering the plants diluted with water acts as a repellent for many insects, because once the solution dries, it forms a uniform whitish patina on the vegetation, which makes it more difficult for the recognition of the plant by the insects. Even if the parasites recognize it and approach it, their movement, feeding activity and egg-laying are hampered and therefore, in practice, their possibility of damage is reduced.

Kaolin is particularly effective in defending against the following insect pests:

  • olive fly

  • psyllium pear

  • psyllium apple

  • fruit moscow

  • cherry fly

  • Aphid virus vectors, such as cucumber mosaic.

It also has some protective effect against the olive mealybug (Saissetia oleae), against scab and fire blight of pumaceae, against snails and certain Lepidoptera, against blossom end rot of tomato and, in part, also against the dreaded Asian bug (Halyomorpha Halys). Finally, it was observed that olive trees treated with kaolin produced better quality oils.

Given the mechanism of action of kaolin, it is important to spray it on the plants before the presence of pests, since its effect is essentially preventive. We can consider 5% of the fruits affected as the average intervention threshold, and not wait for the infestation to spread before using this rock flour.

The defect that kaolin presents, although it is not an intrinsic defect but linked to environmental conditions, is that with the rain it moves away from the vegetation and its effectiveness is annihilated, so it is necessary to repeat the treatment.

The doses of kaolin vary from 2 to 5 kg of rock flour per hectolitre, which translates, in practice, for small surfaces or few plants to be treated, by 20-50 grams/litre of water or, if you prefer to have a medium capacity kaolin pump, 300-750 grams/15 liters.

A precision: the coating of the foliage with kaolin does not prevent the photosynthesis of chlorophyll, it reflects the light and offers the additional advantage of reducing the temperature between the foliage. This protects the plants from too much sun, an advantage that can be found for example in peppers, which are very susceptible to sunburn and for which kaolin can be used specifically for this purpose.

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