Artificially produced fertilizer is problematic for many reasons, including in hobby or home gardens. An ecological and cost-effective alternative, however, is rock dust, even if it is not strictly speaking a fertilizer. You can find out in this article whether and how you can fertilize with stones.
What is rock dust and how is it used in the garden?
Rock flour is a finely ground powder made from various rocks that is used as a soil additive to improve garden soils and to supply plants with important minerals and trace elements. It is not a fertilizer, but an ecological soil additive that can be mixed with compost.
Eating stones is he althy! Rock powder and primary rock powder rich in minerals are he althy for plants and people.
What is rock dust?
As the name suggests, rock dust is very finely ground stones. These have a grain size of less than 0.2 millimeters and are ideal for improving the soil and supplying plants with valuable minerals. The powdery flour is usually made from bas alt, granite, diabase or other deep rocks, and clay minerals and limestone are also added to the mill. The quarries and Germany extract around five million tons every year, providing valuable ecological material.
Rock dust is used as a soil additive, the ingredients of which serve to improve the soil composition and thus indirectly nourish plants. Depending on the source rock, the powder consists of around 80 percent silica (strengthens the plants against diseases and pests) as well as aluminum oxide (between eight and 35 percent) and other trace elements and important minerals. By the way, rock powder made from volcanic ash / lava or clay was already known as a soil improver in Roman antiquity.
Legal regulation
According to the fertilizer law valid in Germany, the various rock powders are listed as soil additives and are therefore distinguished from fertilizers. Soil additives are defined as “substances without significant nutrient content” which, however, are intended to “affect the soil biotically, physically or chemically” with the aim of making fertilizers, for example, work better. The same regulation applies in Austria, only Switzerland specifically mentions magnesium rock powder among fertilizers in the EVD regulation on placing fertilizers on the market.
Background
Difference between primary rock powder and rock powder
Both rock powder and primary rock powder are available commercially, which sometimes leads to confusion. In fact, the rocks used are not of different ages; instead, the difference lies in the composition of the flours:
- Primitive rock flour: consists exclusively of diabase or bas alt
- Rock flour: Mixture of different types of rock such as granite, slate, quartzite, marble or syenite
As a result, the different flours also differ in their ingredients, as the starting stones each have a different composition of the minerals they contain.
Tip
By the way, you can make rock dust from any stone, but not every stone is suitable for plant fertilization. Sand, for example, is strictly speaking also a natural rock powder.
Usage
The ancient Romans already used rock powder to make their soil more fertile. Today the mineral material is used in a variety of ways.
In agriculture
Allotment gardeners often mix rock dust with compost
Rock flour is being used more and more frequently in organic farming, especially since various studies by the North Rhine-Westphalia Chamber of Agriculture have shown that crop yields can be increased in this way. The stone powder is usually mixed with fertilizer or animal manure so that the plants are also supplied with a balanced supply of nutrients. Allotment gardeners, on the other hand, like to mix compost with rock powder for the same reason.
In the garden
In the garden, you should incorporate rock powder into the soil once a year when digging. Depending on the soil and type of rock powder, between 100 and 500 grams per square meter should be applied. How much you actually need depends on the following factors:
- Soil type: clayey, sandy or mixed soil
- pH value: acidic, neutral or alkaline
- Planting: Which plants should be grown, weak, medium or heavy feeders?
Make sure that plant species growing on acidic soils, such as rhododendrons or azaleas, should not be supplied with rock powder or only very little, as this causes an increase in the pH value. However, the flours are very suitable for heavily consuming plants such as tomatoes, as important mineral nutrients are supplied to the soil in the long term and it leaches less.
The following video shows how versatile the possible uses are in the garden as well as in raised beds and also in the garden pond:
Tips for use in the garden
The following tips will help you use rock powder correctly in the garden:
- Bas alt flour is suitable for almost all garden soils.
- For sandy soils you should use bentonite.
- Limestone magnesium is suitable for acidic soils.
- Apply the rock dust in spring or autumn.
- Work it superficially into the soil with the rake.
- Previous and incorporated green manure improves the effect.
- The same applies to a vegetable mulch layer.
- When making the compost, add rock dust straight away to speed up the rotting process.
- When plant manure is used, a handful of rock dust binds unpleasant odors.
- Dust the leaves of the plants with the rock powder, especially after a rain shower or in the morning hours, to protect them from fungal diseases and pests.
For trees
If crops and fruit trees are regularly supplied with rock powder, yields can be noticeably increased. This is not only due to the supply of minerals and trace elements, but above all also to the better he alth of the plants. The product keeps pests and diseases away and is particularly effective where there are no products approved for home gardens against many plant pests. To strengthen the trees, you should mix the stone powder with a little water and pour it directly onto the root area of the trees. The same applies to the otherwise vulnerable roses.
Dosage
The amount of rock dust depends on the type of soil, but also depends on the product selected. The manufacturers provide specific dosage instructions on the packaging, but there are still certain recommendations:
- Calcareous soil: up to 150 grams per square meter
- Acid soil: 200 to 300 grams per square meter
However, whether you use the flour diluted or pure has no influence on the dosage.
Tips for buying suitable rock powder
In principle, purchasing rock dust also makes sense for hobby gardens, as you use less fertilizer and can largely avoid the use of pesticides. The rock dust (€11.00 on Amazon) is usually available in bags weighing 2, 5, 5 or 10 kilograms, although you can choose the larger amount - after all, the material cannot spoil. However, make sure to store it in a dry place! Preferably choose lava flour as it has the highest proportion of iron and other trace elements.
If you want to plant lime-sensitive plants in the garden, we recommend rock powder with a low calcium content.
Various types of rock powder and their areas of application
At this point we will briefly introduce you to the most important rock powders for the garden and explain in which areas they are best used.
Primitive rock flour
Primitive rock flour usually consists of diabase or bas alt, with both types having a similar composition of minerals and trace elements. However, diabase flour contains a little more calcium and is therefore often used for acidic soils. Acidification occurs due to incorrect fertilization, in which mineral fertilizer is applied in excessive amounts or in the wrong composition. However, you can use primary rock flour not only for soil remediation, but also as a compost additive or as an additive for nettle manure and other plant manure. The fine material binds odors and ensures that the garden smells less. On the compost, the flour also supports the microorganisms in their activity, so that the compost decomposes more quickly.
Lava flour
In its chemical composition, lava flour is similar to primary rock flour - after all, all types are volcanic rock - but contains larger amounts of trace elements such as iron. For this reason, it is particularly suitable for supplying heavily consuming crops (such as tomatoes) as well as for a beautiful lawn.
Zeolite flour
If you use zeolite flour, you save on fertilizers
Zeolite is a very special material because it significantly improves the storage capacity of the soil and can thus increase the effect of fertilization. The advantage is that the use of zeolite flour helps you save on fertilizers. But be careful: Zeolite flour has a high alkaline level with a pH value of 8 and should therefore not be used on soils with a neutral or even alkaline pH value. A soil value above 7.5 means that nutrients are no longer delivered to the roots and, in return, the microorganisms living in the soil break down the humus layer too much. Therefore, be sure to measure the pH value of the soil before use.
Clay flour
Applying ground clay - such as bentonite - is useful in sandy soils to improve their ability to store water and nutrients.
Manufacture
Rock powder is obtained by grinding the usually solid source rock. Manufacturers usually use volcanic rock for this purpose, as it contains a particularly large amount of minerals in a composition that is beneficial for plants. These types of rock are most commonly used:
| Rock type | Definition | Appearance | Composition |
|---|---|---|---|
| Bas alt | basic effusion rock, volcanic | dark gray to black | Calcium, Iron, Magnesium |
| Diabas | basic effusion rock, volcanic | greenish | rich in calcium |
| Lava | basic volcanic rock | gray to black | Calcium, Iron, Magnesium |
| Quartz | stable silicon dioxide | different | various minerals |
| Zeolite | Silicate rock | different | various minerals |
| Granite | magmatic deep rock | gray | various minerals |
Other types of rock are also used - for example the clay powder bentonite - but these have different properties and are therefore used differently, for example to increase the garden soil's ability to store water and nutrients. Loosely structured types of rock are best suited, as they later have a fine crumbly structure that holds the water in the soil and gives the roots support.
The selected rocks are first broken into small pieces and only then ground by a rock mill. A system automatically filters out larger pieces of rock. However, the whole process is not quite as ecological as expected, because producing rock powder costs a lot of energy.
Composition and ingredients
The specific composition of a rock powder or primary rock powder depends primarily on the rocks used. Lava flour, for example, has a high iron content, although almost all of the important minerals and trace elements are contained in the various primary rock flours and are available to plants.
The most important components of primary rock flour:
- Magnesium
- Calcium
- Iron
- Silica
- Potassium
- Trace elements such as molybdenum and manganese
A distinction is made between basic and acidic primary rock flour, which is closely related to the calcium content. Basic stone powders contain a lot of calcium, while acidic ones contain little. However, the “acidic” rock powder is not really acidic because its pH value is usually in the alkaline limit. Most primary rock powders have a pH value between 6.5 and 13. Incidentally, rock powders are not suitable for lowering or increasing the pH value because the calcium content is too low. It is best to use garden lime for this purpose.
How it works
Rock powder can only be effective in interaction with the microorganisms in the soil, the soil acids and water. The fine powder is decomposed by the latter two so that theminerals and trace elements are available to the plants and are absorbed via the roots. However, this process is very slow.
However, the rock dust is much more important as asoil improver, which stimulates the soil organisms to form fertile humus. After all, the earth at our feet consists of both dead plant parts and finely ground mineral rock. Such clay-humus soils store water very well without becoming heavy and impermeable to air.
Another important mode of action, especially of granite-based rock powder, is the large amounts of silica, which support plants in their defense against pests and pathogens - especially fungi. For this reason, rock powders are alsoPlant strengtheners
Another rock powder trial against mildew on zucchini. Mildew before, then well powdered. Let's see if it works, says your Gaby zucchini mehltau falschermehltau gesteinsmehl biosaatgut
A post shared by Bio-Saatgut (@gaby.bio.saatgut) on Aug 9, 2018 at 11:42am PDT
Frequently asked questions
Why do you add rock powder to plant manure?
Stinging nettle manure and other plant manures derive their effectiveness from the process of fermentation, which, however, also develops a very unpleasant smell. This odor formation can be prevented by adding rock dust, especially since the plant manure can be enriched with minerals and used to fertilize the garden.
Can you eat rock dust yourself?
There are actually rock powders that are suitable for human consumption. However, do not use products that are declared for the garden, as these are contaminated with other substances. The mineral powders are subject to food law and should be labeled accordingly.
Does rock dust also help against the boxwood moth?
Many gardeners swear by using rock dust against the box tree borer. To keep this annoying pest away, you should dust the bushes with the powder early in the year and repeat the treatment regularly throughout the growing season.
Tip
A ring of rock dust around endangered plants keeps voracious slugs away. The product also helps against flea beetles, aphids and other plant lice, woodlice, ants and the Colorado potato beetle.
