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Origin and effect

"Lime makes rich fathers and poor sons," our grandfathers already knew. The saying puts it in a nutshell: If you bring out too much lime in the garden, you promote the extraction of humus. In the short term, many nutrients will be released, but in the long term you will leach out the soil. When the humus content fades, the soil structure deteriorates and the storage capacity for air, water and nutrients decreases.
By contrast, lime fertilization with a sense of proportion has many beneficial effects: the lime neutralizes the acidity of the soil and thus counteracts creeping soil acidification. It also combines the clay particles to larger crumbs and promotes the biological activity of the microorganisms. The indirect effects are even more varied: The nutrients supplied as fertilizer are better absorbed by the plants, the flocculated clay crumbs improve the soil structure and thus the storage capacity for water and air. This in turn reduces the risk of sludge and leads to a faster warming of the soil in the spring.

From a chemical point of view, lime is a compound of the element calcium (Ca). The chemical element is one of the most important mineral building blocks of animals and plants. In animals and humans calcium is found in higher concentrations in the bones and teeth, in plants calcium is an important building block of the cell walls. Calcium occurs in nature in various rock types and sediments almost exclusively as so-called carbonate lime and carries the chemical name calcium carbonate (CaCO3). Most calcium fertilizers are based on this raw material. The so-called lime deposits in the soil are almost exclusively deposited sediments of the ancient seas, which are the lime-rich shells of various marine life such as crabs, shells, snails and sepia. Over the course of millions of years, rock strata have formed. Where they are in a particularly pure form, they are often mined for the production of cement and just lime fertilizer.

Pointer plants reveal lack of calcium

Various pointer plants provide hints on the lime balance of your soil. Reliable indicators for a low calcium content are, for example, mustard, rabbit clover, three-leaved honorary prize, dog chamomile, little sorrel, various moss species, sand pansies and field horsetail. Also some garden plants show by growth disturbances lime deficiency: Dried shoot tips and yellow discolored young leaves are typical characteristics. In tomatoes, lime deficiency leads to late blight, while apples and quinces often show small brown spots on the skin on acidic soils - the so-called stem, which often causes brown spots in the flesh.

Sorrel Rumex acetosella

Small sorrel (Rumex acetosella) is a pointer plant for calcareous soils

A soil analysis provides information

To determine the calcium content, you should have an analysis of your soil done in the soil laboratory. For a rough assessment, however, a simple test set from the garden trade or - much more expensive - an electronic pH meter is sufficient. However, the result is nothing more than a clue, because the pH says only limited about the actual lime and acidity of the soil. Loamy soils have a much better buffering effect than sandy soils - meaning that their acidity at the same pH can be significantly higher.

Soil type and pH

Loam and loess soils in the vegetable garden should have a pH of 7, sandy loamy soils at pH 6.5 and loamy sandy soils at pH 6. Pure sandy soils should not fall below a pH of 5.5. For grass and perennial beds, the limit values ‚Äč‚Äčfor all four types of soil can be set at about 0.5 lower. Rhododendron and other so-called moor bed plants and summer heathers, hydrangeas and camellias can not tolerate lime, so you should abstain from liming. Last but not least, the pH value of loamy soils must always be slightly higher, because below pH 5.5 a chemical process takes place that is detrimental to many plants: The soil acid decomposes the clay minerals and dissolves the aluminum salts embedded in them. The strongly increasing aluminum concentration in the soil leads to growth disturbances in many plants.

Kalkd√ľngung with scatter carriage

Even heavily acidified lawns occasionally need lime. It is suitable for spreading a spreader - but liming does not help against moss, because these plants are very adaptable to the pH of the soil

Guide values ‚Äč‚Äčfor calcium fertilization

Although precise lime fertilization is only possible after previous soil examination, there are a few relatively reliable orientation values. If the specified pH limits are slightly undercut, a so-called maintenance liming is recommended. This only replaces the lime that has been lost through leaching or absorption by the plants.If you sprinkle 150 grams of calcium carbonate per square meter every three years, the lime content and thus the pH of the soil remain stable. If the pH of your soil is below the limit for a complete pH level, you will need to use significantly more lime, depending on the type of soil. For sandy soils, it takes about 250 grams of carbonate of lime per square meter to raise the pH by one level. In clay soils, however, even twice the amount may be necessary. In this case, you should distribute the limestones on two appointments with about half a year distance.

Calcium fertilizer at a glance

Depending on the type of soil and the desired nutrient composition, you have the choice between different calcium fertilizers for the garden:

garden lime

This is ground, hardly soluble limestone made of carbonate lime with a low magnesium content. Garden lime is used for light and medium soils and should be used in autumn or winter. It unfolds its effect slowly and gently. Carbonated lime with a high magnesium content is also available under the trade name "Dolomitkalk". It is suitable for plants with high magnesium requirements, for example for conifers. For regular maintenance liming, however, the magnesium content of the garden lime used should not exceed ten percent.

rock flour

Rock minerals contain a lot of carbonate of lime, magnesium, potassium and various trace elements. Depending on the origin and source rock, however, the composition can vary greatly. The nutrients must first be made available to plants by microorganisms, so the effect unfolds quite slowly. Tip: If you enrich your compost with rock flour before it decomposes, you can usually forego direct lime treatment on the garden floor.

rock flour

Rock flour is one of the most important natural soil auxiliaries


Burnt lime is formed by vigorous heating of carbonate of lime. At temperatures above 800 degrees Celsius, carbon dioxide is released leaving behind calcium oxide (CaO). This lime form is mainly used in agriculture for heavy soils - often for a short time before sowing because it works very fast. For hobby gardeners burnt lime is not recommended, because it is because of its strong corrosive effect (pH 12-13) in handling very problematic and can lead to blindness in case of eye contact. In addition, it can temporarily damage the soil life.

slaked lime

If burnt lime is extinguished by adding water, slaked lime is produced. He carries the chemical name calcium hydroxide (CaOH2). Extinguishing lime does not work as fast as burnt lime and is used in agriculture to lime medium-heavy soils. This lime form is highly corrosive like burnt lime and not suitable for the home garden.


Lime marl contains up to 70 percent carbonate of lime and up to 30 percent clay. It is particularly suitable for improving the storage capacity of very light sandy soils. Lime marl has a slow and lasting effect because the clay contributes to stabilizing the pH of the soil.


These are mostly coral deposits of red algae. Algae lime consists of approximately 80 percent carbonate of lime, has a relatively high magnesium content and is rich in trace elements such as manganese or boron. So that the trace elements can be optimally utilized by the plants, algae lime should be applied during the growing season.

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