What are the disadvantages of limestone soil

Quicklime: A dangerous fertilizer

Regular, well-dosed amounts of lime are important to protect the garden soil from acidification and to improve its fertility. But there are different types of lime with individual properties. Some hobby gardeners regularly use quicklime, a particularly aggressive type of lime. Here you can read what quicklime actually is and why it is better to avoid it in the garden in most cases.

Manufacture of quicklime

First a small chemical excursion: quicklime is produced by heating carbonate of lime. At temperatures above 800 degrees it is "deacidified" by the carbon dioxide (CO2) is driven out. What remains is calcium oxide (CaO), which is strongly alkaline with a pH value of 13, also known as unslaked lime. When it comes into contact with water, it is transformed into calcium hydroxide Ca (OH) in a chemical reaction which in turn releases a lot of heat (up to 180 degrees Celsius)2), the so-called slaked lime.

The main area of ​​application of quicklime is in the construction industry for the production of plaster, mortar, lime paint, sand-lime bricks and cement clinker. Quicklime is also used in steel production and the chemical industry. As a fertilizer, quicklime is mainly used in agriculture to improve heavy soils and raise the pH value in the soil. Quicklime is available from specialist retailers as a powder or in granular form.

What is the use of quicklime?

Calcium plays an important role in soil health. It promotes fertility and improves acidic soils by increasing the pH. In contrast to slaked lime or carbonate lime, so-called garden lime, quicklime works particularly quickly and effectively. Heavy and silty soils are loosened by the introduction of lime - this effect is also known as "lime blasting". Quicklime also has a soil hygienic effect: snail eggs and various pests and pathogens can be decimated with it.

Quicklime is a hazardous substance

As already mentioned, unslaked lime reacts strongly with water, i.e. with rain as well as with irrigation water or high air / soil moisture. This reaction releases a lot of heat that can literally burn plants and microorganisms. Lawns or planted beds in the garden should therefore under no circumstances be treated with quicklime. Do not mix unslaked lime with organic fertilizers such as manure or guano, as the reaction releases harmful ammonia. Quicklime is also dangerous for humans: it has a strong corrosive effect on the skin, mucous membranes and eyes, both when it is removed and when it is not extinguished and should therefore only be applied with appropriate safety precautions (gloves, protective goggles, respirator) and never inhaled. In the construction industry, quicklime was previously only cleared on site, which has repeatedly led to accidents. The granular form is much less dangerous than the fine lime powder.

Use quicklime correctly in the garden

Before lime fertilization can take place in the garden, the pH value of the soil must first be determined. It is very difficult to reverse an over-fertilization with calcium. Liming with quicklime may only make sense at values ​​below pH 5 and very heavy, clayey soil. The dosage is based on the difference between the actual and the target value and the weight of the soil.

In higher doses, unquenched lime burns any organic material with which it comes into direct contact through the soil moisture before being extinguished. Therefore, quicklime in the garden is only suitable for fallow soils such as harvested vegetable patches or areas that are to be replanted. Here it is very effective in killing pathogens without putting too much strain on the soil, as is often the case with chemical pesticides. In the slaked state, the calcium hydroxide has an invigorating effect on the soil and promotes the growth of the cultivated plants. It is recommended for beds that are contaminated with soil-borne pathogens such as the coal hernia. This disease occurs much less frequently after liming.

When the lawn is full of moss, it is often recommended that you limewash it. However, the lime is not a panacea and can even promote moss growth. With these tips, lawn care with lime is a success.

After spreading, quicklime and all other forms of lime are worked into the soil on the surface, but not submerged. After that, the soil should rest for four to six weeks. Sometimes it is recommended to add quicklime to the compost heap to kill weed seeds and lime the humus. The objection to this is that quicklime in the compost not only destroys pests but also the microenvironment close to the surface, which can greatly slow down composting. In addition, the strong heat development must be taken into account, which can set a closed compost system on fire.


Basically, the use of quicklime in the garden is a dangerous matter and should never be done without protective clothing, gloves and goggles. Incorrect application can endanger human, animal and plant health. Since the use of quicklime only makes sense in very limited areas, we recommend using garden lime for soil liming. This is gentler on the environment and easier to use. If you don't want to do without the herbicidal and fungicidal effect, you should use calcium cyanamide instead of quicklime.