Man-made fertilizer is problematic for many reasons, including in hobby or home gardens. An ecological and cost-effective alternative, on the other hand, is rock flour, even if strictly speaking this is not a fertilizer. In this article you can find out whether and how you can fertilize with stones.

Rock flour is a fertilizer that helps improve soil quality

Table of Contents

Show all
  1. the essentials in brief
  2. What is rock flour?
  3. use
  4. dosage
  5. buying tips
  6. Different types of rock dust
  7. manufacturing
  8. composition and ingredients
  9. mode of action
  10. frequently asked Questions
  11. Why is rock flour added to plant manure?
  12. Can you eat rock flour yourself?
  13. Does rock flour also help against the box tree moth?

    14. Eating stones is healthy! Rock flour rich in minerals (14.13€) and primary rock flour is healthy for plants and people.

    the essentials in brief

    • Rock flour is finely ground stones that provide plants with minerals
    • Rock flour is not a fertilizer, but a soil additive
    • Depending on the soil, 100 and 500 grams per square meter are worked in once a year; mixing with compost is a common practice

    What is rock flour?

    As the name suggests, rock powder is very finely ground stones. These have a particle size of less than 0.2 millimeters and are ideal for improving the soil and supplying the plants with valuable minerals. The powdery flour is mostly made from basalt, granite, diabase or other plutonic rock, but clay minerals and limestone are also used in the mill. The quarries and Germany produce about five million tons every year and thus provide valuable ecological material.

    Rock flour is used as a soil additive, the ingredients of which serve to improve the composition of the soil and thus indirectly to supply plants. Depending on the source rock, the powder consists of around 80 percent silicic acid (strengthens the plants against diseases and pests) and aluminum oxide (between eight and 35 percent) and other trace elements and important minerals. Incidentally, rock flour made from volcanic ash / lava or clay was already known as a soil conditioner in Roman antiquity.

    Legal regulation

    According to the fertilizer law in force in Germany, the various mineral powders are listed as soil additives and are therefore distinguished from fertilizers. Soil additives are defined as "substances with no significant nutrient content" which, however, are intended to "affect the soil biotically, physically or chemically" with the aim of making fertilizers, for example, more effective. The same regulation applies in Austria, only Switzerland mentions in particular magnesium powder as fertilizers in the EVD ordinance on the placing on the market of fertilizers.

    background

    Difference between primary rock flour and rock flour

    Both rock flour and primary rock flour are commercially available, which sometimes leads to confusion. In fact, the rocks used are by no means of different ages, instead the difference is in the composition of the flours:
    • bedrock meal: consists exclusively of diabase or basalt
    • rock flour: Mixture of different rock types such as granite, slate, quartzite, marble or syenite

    As a result, the various flours also differ in their ingredients, since the starting stones each have a different composition of the minerals they contain.

    tips

    Incidentally, rock flour can be made from any rock, but not all of it is suitable for plant fertilization. Strictly speaking, sand, for example, is also a natural rock powder.

    use

    Even the ancient Romans used rock powder to make their soil more fertile. Today, the mineral material is used in many different 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 harvest yields can be increased in this way. Fertilizer or animal manure is usually added to the rock flour so that the plants are supplied with a balanced supply of nutrients at the same time. Allotment gardeners, on the other hand, like to mix compost with rock dust for the same reason.

    In the garden

    In the garden, you should work rock flour into the soil once a year when digging. Depending on the soil and the type of rock dust, 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 cultivated, weak, medium or heavy consumers?

    Note that plant species growing on acidic soils, such as rhododendrons or azaleas, should not be supplied with rock flour, or only very little, as this causes the pH value to rise. However, the flours are very well suited for plants that consume a lot, such as tomatoes, since important mineral nutrients are supplied to the soil in the long term and it leaches out less.

    The following video shows how versatile the possible uses are in the garden, in the raised bed and also in the garden pond:

    youtube

    Tips for use in the garden

    The following tips will help you to use rock flour in the garden correctly:

    • Basalt 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 flour in spring or autumn.
    • Work it superficially into the soil with the rake.
    • A previous and incorporated green manure improves the effect.
    • The same applies to a vegetable mulch layer.
    • When preparing the compost, add rock dust to speed up the rotting process.
    • With plant manure, a handful of rock flour binds unpleasant odors.
    • Dust the leaves of the plants with the rock powder, especially after a downpour or in the morning hours, to protect them from fungal diseases and pests.

    For shrubs

    If useful plants and fruit trees are regularly supplied with rock flour, the yields can be noticeably increased. This is not only due to the supply of minerals and trace elements, but above all to the better health of the plants. The agent keeps pests and diseases away and is particularly effective where there are no agents approved for home gardens against many plant pests. To strengthen the trees, you should mix the rock flour with a little water and pour the trees directly onto the root area. The same applies to the otherwise so susceptible roses.

    dosage

    The amount of rock flour depends on the type of soil, but also depends on the product selected. The manufacturers give specific dosage instructions on the packaging, but there are certain recommendations:

    • Calcareous soil: up to 150 grams per square meter
    • acid soil: 200 to 300 grams per square meter

    However, whether you apply the flour diluted or pure has no influence on the dosage.

    Tips for buying a suitable rock flour

    In principle, the purchase of rock dust also makes sense in the hobby garden, since you use less fertilizer and can also largely do without the use of pesticides. Rock dust is usually available in bags weighing 2.5, 5 or 10 kilograms, although you can choose the larger quantity - after all, the material cannot spoil. However, make sure to store it in a dry place! Preferably choose lava flour, as this has the highest proportion of iron and other trace elements.

    If you want to put lime-sensitive plants in the garden, rock dust with a low calcium content is recommended.

    Different types of rock powder and their areas of application

    At this point we will briefly introduce you to the most important rock dust for the garden and explain in which areas they can best be used.

    bedrock meal

    Prehistoric rock powder usually consists of diabase or basalt, 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 overly acidic soils. Acidification is caused by incorrect fertilization, in which mineral fertilizers are applied in excessive amounts or with 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 there is less smell in the garden. The flour also supports the microorganisms in their activities on the compost, so that the compost decomposes more quickly.

    lava flour

    In terms of its chemical composition, lava powder is similar to primary rock powder - after all, all types are volcanic rock - but it contains larger amounts of trace elements such as iron. For this reason, it is particularly suitable for supplying crops that consume a lot (e.g. tomatoes) and for a beautiful lawn.

    zeolite flour

    Those who use zeolite flour 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 of this is that the use of zeolite flour helps you save on fertilizers. But be careful: With a pH value of 8, zeolite flour has a high alkaline level and should therefore not be used on soil with a neutral or even alkaline pH value. A soil value above 7.5 means that nutrients are no longer released 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 of the soil before use.

    clay flours

    The application of ground clay - such as bentonite - is useful in sandy soils to improve their ability to store water and nutrients.

    manufacturing

    Rock flour is obtained by crushing the usually solid parent rock. Manufacturers usually use volcanic rock for this purpose, as it contains a particularly large number of minerals in a composition that is favorable for plants. The most common types of rock are:

    rock type definition Look composition
    basalt basic igneous rock, volcanic dark gray to black Calcium, Iron, Magnesium
    diabase basic igneous rock, volcanic greenish rich in calcium
    lava basic volcanic rock gray to black Calcium, Iron, Magnesium
    quartz stable silica different different minerals
    zeolite silicate rock different different minerals
    granite magmatic plutonic rock Gray different minerals

    Other types of rock are also used - for example bentonite powdered clay - but these have different properties and are therefore used differently, for example to increase the storage capacity of the garden soil for water and nutrients. Loosely structured types of rock are best suited, as they later have a finely crumbly structure that keeps the water in the ground 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 rocks. However, the whole process is not quite as ecological as thought, because the production of rock flour costs a lot of energy.

    composition and ingredients

    The concrete composition of rock powder or primary rock powder depends primarily on the rocks used. Lava flour, for example, has a high iron content, although in principle almost all the important minerals and trace elements are contained in the various primary rock flours and are available to the plants.

    The most important components of bedrock powder:

    • 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 rock flours contain a lot of calcium, while acidic ones contain little. However, the "acidic" rock flour is not really acidic, because its pH value is usually in the alkaline border area. Most primary rock dust has a pH value between 6.5 and 13. Incidentally, rock dust is not suitable for lowering or increasing the pH value because the calcium content is too low for this. It is best to use garden lime for this purpose. (9.70€)

    mode of action

    Rock dust 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 the minerals and trace elements are available for the plants and are taken up by the roots. However, this process is very slow.

    Much more important is the rock flour than soil conditioner, which stimulates soil organisms to form fertile humus. After all, the earth at our feet consists of both dead plant matter 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 of granite-based rock flour is the large amount of silicic acid, which supports the plants in their defense against pests and pathogens - especially fungi. For this reason rock flours are at the same time also plant strengthener.

    frequently asked Questions

    Why is rock flour added to plant manure?

    Nettle manure and other plant manure get their effectiveness from the process of fermentation, which, however, also develops a very unpleasant odor. This odor can be prevented by adding rock flour, especially since the plant manure can be enriched with minerals and used to fertilize the garden.

    Can you eat rock flour yourself?

    There are actually rock flours that are suitable for human consumption. However, do not use any agents 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 flour also help against the box tree moth?

    Many a gardener swears by the use of rock flour against the box tree moth. To keep this pesky pest away, you should dust the bushes with the powder early in the year and repeat the treatment regularly throughout the growing season.

    tips

    A ring of rock dust around endangered plants keeps voracious slugs away. Furthermore, the agent also helps against flea beetles, aphids and other plant lice, woodlice, ants and the Colorado potato beetle.

Category:

Garden design