Rock flour

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As the name already suggests, rock flour, which is often also sold under the name Urgesteinsmehl commercially, with a grain size of about 0.063 millimeters a very finely ground material and is usually obtained from basalt or lava rock. It is a so-called soil additive, which enriches the soil with mineral trace elements. The silica they contain makes them more resistant to pests and diseases, for example. In addition, direct treatment of the plants with rock flour reduces the activity of various pests. However, since minerals contain no or only very few main nutrients, they are not among the classic fertilizers. Depending on the source rock, the soil adjuvant usually consists mostly of silicic acid (about 80 percent), followed by aluminum oxide (between 8 and 35 percent) and other minerals and trace elements. In nature, ground rock meals also occur - for example, as abrasions of migrating glaciers.

Especially in organic gardens, the substrate is used as a tool to improve soil quality. It is also often used in the production of vegetable fodder because it softens the strong odor somewhat.

Production of rock flour

Rock flour is obtained by grinding the most massive source rock. These are mostly rocks of volcanic origin, as they contain many different minerals. Under high energy consumption, the starting material is first broken into small pieces. The pieces are then ground to a fine powder by a rock mill; too large rock constituents are screened out.
Basalt, diabase, lava, quartz, zeolite and granite are the most commonly used source rocks, although the latter is rarely used.
Also clay flour such as bentonite are counted among the original rock flours. However, they have different characteristics, which is why they are used for other applications - for example, to increase the storage capacity of the soil for nutrients.


The substances present in the rock flour and their proportions depend heavily on the starting rocks used. For example, lava flour has a significantly higher proportion of iron compounds than diabase or basalt flour. Basically, it can be said that numerous trace elements - which are released to the ground in the medium or long term - are contained and thus finally available to the plants. Minerals such as magnesium, calcium and iron as well as silicic acid, potassium and some trace elements such as molybdenum and manganese are important constituents of rock minerals.

rock flour

Rock flour is one of the most important natural soil auxiliaries

The different types of rock flour

Classic ground rock minerals mainly consist of ground basalt or diabase. The flours from basalt are often a little darker than diabetic flours, but have a similar composition of minerals or trace elements.
Urgesteinsmehle be used in the garden and in organic agriculture to improve the soil structure and for the supply of minerals such as magnesium and iron. A fine degree of crushing is very important because the minerals must be transferred to the water phase so that they are absorbed by the roots of the plant. The fine rock particles must be completely weathered before they are available to the plants.
Mineral flours based on diabase are often used to cleanse acidified soils due to their high calcium content. Stone flours from basalt or granite, on the other hand, help to acidify strongly alkaline soils. Such minerals are also useful as a composting addition: Here, the fine flours mainly increase the activity of the microorganisms found in the compost. In addition, the enzyme activity is positively influenced by the trace elements, whereby the organic material in the compost heap can be degraded faster and digested by the microorganisms. The use of lava flour is similar to that of other minerals. In addition, this substrate is of great advantage in the supply of turf or starved animals such as tomatoes, since it contains a large amount of micronutrients.
Ground minerals such as bentonite, for example, promote the formation of clay-humus complexes, thus improving the storage of water and nutrients in sandy soils.
Zeolite flour also serves primarily to improve the storage capacity of the soil. The flour is able to deliver various nutrients to the plant when needed. When using zeolite flour, however, it should be noted that this substrate is quite alkaline in soils with pH values ​​above eight.
Above all, in soils with a near neutral pH, an oversupply of this stone meal can have a negative effect on plant growth.Excessively high pH values ​​(over 7.5) ensure that some nutrients can not be released to the plant roots, and that the microorganisms therefore break down too much humus. For large-scale use of zeolite flour, therefore, the pH value of the soil should be measured beforehand. Zeolite is much more expensive than other minerals. However, by using the fertilizer amount can be reduced, so you ultimately save costs.

Use in the garden

You can either sprinkle and incorporate minerals into or dissolve them in water and vegetable manure. If you sprinkle it regularly over your compost, it also gets into the ground with the humus in spring. The material is absorbed only after complete decomposition of the plant roots - therefore it is not suitable for the short-term remedy of a trace element deficiency, but unfolds its effect in the long term. Since an oversupply of trace elements is hardly possible, it is best to extract rock flour every year in small quantities. Thus the positive effect on the growth and the health of the plants develops long-term and lasting.

Although not all crops respond equally to the addition of rock flour, if grown appropriately, you can expect higher yields in the growing of fruit trees and vegetables. On the other hand, if you do without application for three years, the effect will decline significantly.

Rock flour Nettle

Urgesteinsmehl alleviates the unpleasant odor of Pflanzenjauchen

Rock flour for woody plants

Rock flour can also serve well in fruit growing: especially where pest infestation can no longer be combated with conventional means or there are currently no suitable or approved agents on the market, the health of the woody plants can be strengthened in the long term by using rock flour. To spread, sprinkle the stone meal either on a windless day by hand or mix it with some water and then pour it into the root area of ​​the trees and shrubs.

Dosing rock flour correctly

The amount of rock flour that you spout pure or diluted in their garden varies from floor to floor. For calcareous soils, up to 150 grams per square meter are common, for acidic soils 200 to 300 grams of rock flour per square meter are recommended. The correct dosage depends on the product and is usually indicated on the packaging.
If you want to do something good for plants that feel good on acid soil, you should only use small amounts. Growths such as rhododendrons may well benefit from rock flour, but you should not use basic products. Under certain circumstances, it can lead to lime chlorosis, as certain nutrients can only be absorbed in small quantities. In the case of lime-compatible heavy-eaters such as tomato, on the other hand, the amount of rock-flour can be quite a bit larger.

Neudorff rock meal

Urgesteinsmehl is available from several manufacturers

This is to be considered when buying rock flour

The purchase of rock flour is worthwhile for all hobby gardeners, since the substrate has a wide range of applications. Above all, if you want to cultivate your soil sustainably, rock flour is a good product to improve the soil structure in your garden. There is a large selection of rock flours - but often the products differ only by their name. When buying rock flour, pay attention to the low calcium content of calcium, if your soil has a pH in the alkaline range or if you want to supply it with lime-sensitive plants.
The price of rock flours varies depending on the manufacturer and product. Usual are 2.5, 5 and 10 kilogram sacks of the soil adjuvant, whereby the price per kilogram is about one euro. Lavender flour is usually a bit more expensive, but should preferably be used if possible. This flour usually has the highest iron content of all minerals and also contains some other very important trace elements.

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