Kaolin, zeolite, bentonite

Kaolin, zeolite, bentonite rock flours

Kaolin, zeolite, bentonite, rock powders are widely used in agriculture, especially in organic farming, where they are a valid alternative to fungicidal and insecticidal products for the vegetable garden and orchard.

These flours or powders are minerals that are mechanically refined, they function as a sort of mechanical obstacle to the harmful action of some parasites, without causing negative side effects on the environment and for this reason they can be used for natural cultivation.

Let’s see which are the most common rock flours for agricultural use, how to choose them and what are the best ways to use them, taking full advantage of them for the organic vegetable garden and orchard. In particular, we focus on kaolin, zeolite and bentonite which are the three most used mineral powders and which can prove to be more useful.


Kaolin is a mineral of sedimentary origin that disperses easily in water, is mainly composed of aluminum and silicon and has the appearance of a chemically inert white powder.

Sprayed on plants diluted in water, it works as a repellent against many insects, because once the solution dries, it forms a uniform whitish patina on the vegetation, such as to make it more difficult for insects to recognize the plant. Even if the parasites recognize it anyway and approach it, then their movements, trophic activity and oviposition activity are hindered and therefore in practice their possibility of damage is reduced.

Kaolin is especially effective in defending against the following harmful insects:

  • Moscow of the olive tree
  • Psylla of the pear tree
  • Psylla of the apple tree
  • Fruit fly
  • Cherry fly
  • Virus-carrying aphids, such as that of the cucumber mosaic.

It also has a certain protective effect against the half-peppercorn cochineal (Saissetia oleae) of the olive tree, against scab and bacterial fire blight of the pome fruit, against snails and some lepidoptera, against the apical rot of the 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 plants before the presence of parasites, because its effect is essentially of a preventive type. We can consider 5% of the affected fruits as an average intervention threshold, and not wait for the infestation to spread before using this rock meal.

The defect that kaolin presents, even if it is not an intrinsic defect but linked to environmental conditions, is that with the rain it was removed from the vegetation and its effectiveness is annihilated, so the treatment must then be repeated.

The doses of use of kaolin vary from 2 to 5 kg of rock flour per hectolitre, which translate, in the practice of small surfaces or a few plants to be treated, in 20-50 grams / liter of water or, if you prefer refer to a backpack pump of medium capacity, 300- 750 grams / 15 liters.

A clarification: covering the foliage with kaolin does not prevent chlorophyll photosynthesis, it reflects light and offers the additional advantage of reducing the temperature between the foliage. This protects the plants from excessive insolation, an advantage that is found, for example, on peppers, which are very prone to sunburn and for which kaolin can be used specifically for this purpose.

The zeolite

The term zeolite refers to a mineral of volcanic origin composed mainly of silicon oxide and aluminum oxide, which is extracted from natural deposits. There are many types of zeolites, which is why talking about them in general would be more correct to indicate them in the plural as zeolites. The main feature that unites them is the presence of many empty spaces in the granular and crystalline microporous structure, which allow a good cation exchange and the absorption of a large amount of water.

This aspect can be exploited, in treatments on plants, to reduce the humidity present and create an unfavorable microenvironment for the threat of fungal pathogens. In practice, the veil of water that remains on the plants with rain or dew is dried more quickly. Furthermore, zeolite helps in the healing of micro-wounds of plants, which are preferential entry sites for pathogens. There are particular families of zeolites called Chabasiti which form a physical-mechanical barrier that also protects against harmful insects, and with these products the protection of crops is therefore more extensive and complete.

In organic vineyards, treatments with zeolite are very effective against downy mildew and botrytis, but the effectiveness is also found in fruit growing and in the vegetable garden, depending on the different specific products for different crops.

Commercial products based on zeolite, such as the Zeolite Organic Fertilizer Compost Agent All Purpose Absorbent are highly micronized rock flours and therefore such as to allow complete wetting of the plants in the distribution. The recommended treatments are liquids with variable dosages depending on the crops, and indicatively the doses to treat the vegetables are 0.5-08 hg of flour / 100 liters. For small extensions, such as those of amateur gardens and orchards, treatments are usually carried out with knapsack pumps, and in this case it is important to use one equipped with metal nozzles, because zeolite can have an abrasive effect on plastic nozzles and occlude them.

But the use of zeolites is not limited to phytosanitary defense and is also valid in fertilization, as a natural mineral fertilizer, to be spread in handfuls in the garden, in fruit tree transplant holes, in compost: zeolites, with their precious micronutrients (iron, magnesium, manganese etc.) contribute to a balanced soil nutrition, which is a prerequisite for the good health and productivity of cultivated plants. Zeolite therefore also lends itself to being used as a soil improvement, as we have detailed in the article on zeolite as a substrate.


The name bentonite includes various clays of variable composition, all of volcanic origin particularly rich in microelements and with the characteristic of absorbing water. Bentonite is used alone or mixed with sulfur to fight the gray mold (Botritis cinerea) of the vine (which also affects strawberries, raspberries and other vegetable and fruit species). On the vine, however, the treatments with this pulverized mineral must be carried out before the closure of the bunch, preferably in powdery form (not diluted in water).

Bentonite is also used for the preparation of a special log pulp used in biodynamic agriculture and which is composed of 1/3 of bentonite, 1/3 of fresh cow manure without the addition of straw and 1/3 of silica sand. all mixed with a decoction of horsetail to the right consistency. This fluid paste, of which there are also variants in the formulation, is literally spread in brushstrokes on the trunks of adult fruit plants towards the end of winter and has the function of nourishing and stimulating the cambium, or the subcortical layer where the new cells. Bentonite finds further use as an adjuvant to copper in treatments against downy mildew.

For liquid treatments with bentonite a variable dosage between 300 and 700 grams of rock flour per hectolitre is used, while for powder treatments 20-40 kg / ha is calculated.

The use of rock powders in organic farming

As we said, rock flours are products that can be used in organic farming, without affecting the environment. Annex 2 of the recent Ministerial Decree 6793 of 2018, which integrates the European legislation on organic agriculture for Italy, lists in a table all the “Products used as corroborants, enhancers of the natural defenses of plants”, and among these is also present is the “Stone or rock dust”, which is better described as “Product obtained as it is by the mechanical grinding of various types of rocks, whose original composition must be specified”. In the same table, in the column showing the methods and precautions for use, it is clarified that the dust must be free from polluting elements. It is possible to deduce the prohibition for certified farms to mix other chemical substances not allowed in organic farming with rock flours.

For private cultivation of vegetable gardens and orchards where it is grown for self-consumption, as well as for small non-certified mixed farms that have essentially chosen the path of sustainable agriculture, the products allowed in organic farming are however an important reference point. for a defense against adversity that respects the environment and generates healthy and genuine products.

You may be interested to read about the Carolina reaper grow guide/ Naga morich pepper grow guide/ Calabrian chilli grow guide/ Habanero pepper cultivation/ Jalapeño pepper blogpost/ Germinating seeds Recipe/ Stuffed baguette with peppers recipe/ Italian roasted peppers recipe/ Hot pepper jam recipe/ Care plants with propolis blogpost/ Ice cream pudding recipe.

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