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It is said that anyone who grows vegetables or herbs in the garden should lime their garden. Even gardeners with a lawn are familiar with the recommendation to whitewash the green area regularly. But what is the actual advantage? Does every bed or lawn have to be limed and how much lime do you need? We answer these and many other questions in this article on the subject of garden lime.
mode of action
Garden lime is used to improve the soil. It provides the plants with vital calcium and is involved in making nutrients in the soil available to the plants. This makes the plants more resilient. At the same time, the pH value in the soil is raised to counteract acidification in the soil. Liming the garden soil has a whole host of benefits, including the following.
- Garden lime creates a finely crumbly soil
- provides stability in the ground by improving soil structure
- protects the garden soil from siltation
- strengthens the plants so that they are less susceptible to diseases
- Regulates the acidity of the soil by neutralizing the acid
- promotes the proliferation and biological activity of important soil organisms
- impedes the growth of many unwanted lawn weeds
- Promotes rapid warming of the garden soil in spring
But spreading garden lime does not only have advantages. Applying too much lime fertilizer in the garden promotes the rapid decomposition of humus. This releases a lot of nutrients in the short term, but leaches out the soil in the long run. If the humus disappears, the structure of the garden soil deteriorates and the storage capacity for water and nutrients decreases.
Optimum pH values
Depending on the type of soil, there are empirical values at which value the optimal pH value in the soil should be. If there is no lime, the pH is too low. Please never lime areas in your garden where plants grow that require a highly acidic soil environment. These include, for example, rhododendrons, azaleas or blue hydrangeas.
- Clay soil: pH of 7
- sandy loam soil: pH of 6.5
- loamy sandy soil: pH values around 6
- pure sandy soil: pH about 5.5
Perform soil test
There are special lime tester sets for the garden soil on the market, with which even gardeners without chemical training can measure the exact pH value of the soil by means of a coloring reaction. A soil sample is taken according to the instructions and placed in a glass tube. It is then slurried with distilled water and a test tablet is added. After shaking, wait for the solids to settle and compare the supernatant with a color chart. The test can be used for vegetable beds, lawns or even flower beds. There are also tests that use test strips with a color scale instead of a tablet.
Certain plant species also provide indications of the lime content in the soil. If you look a little closer, you might not need to do a soil test. There are so-called indicator plants, which are plants that only feel comfortable under very specific conditions. There are also indicator plants that indicate a lack of lime or high amounts of lime.
Indicator plants for lime deficiency (like a rather acidic soil):
- Farmer's mustard (Teesdalia nudicaulis)
- Hare clover (Trifolium arvense)
- Dog chamomile (Anthemis)
- Sorrel (Rumex acetosa)
- Horsetail (Equisetum)
- Pansies (Viola)
Indicator plants for high soil pH (like calcareous soils):
- Nettle (Urtica)
- Shepherd's knuckle (Capsella bursa-pastoris)
- Deadnettle (Lamium)
amount of lime
How much lime do you need?
The question that most hobby gardeners ask themselves is how much garden lime you actually need. "A lot helps a lot" is the wrong motto here. Because if you use too much lime, you usually have the opposite of what you hope for. Too much garden lime is harmful to many plants. Not only because it converts various nutrients into a form that is no longer soluble in water. This means that these nutrients, such as iron, are no longer available to the plants, which means that other deficiency symptoms can occur. The pH of most soils naturally decreases over time. It is only very rarely observed that it rises.
If the values for the individual soil types are slightly below the above values, you will of course have to apply less garden lime than if the values are significantly below. Therefore, a distinction is made between healthy liming and maintenance liming.
As long as the plants on the garden soil do not show any signs of undersupply, it is advisable to carry out the liming in such a way that the existing level of supply is maintained. With this so-called maintenance liming, only the optimal pH range should be maintained.
A somewhat more radical measure is always necessary when there are increased signs of a clear undersupply of the plants. Very acidic soil (pH 5 or below) is unfavorable for the soil structure. The crumbly structure is lost and the soil loses the ability to drain water well. The result is, on the one hand, a silting up of the soil and, on the other hand, the microorganisms are inhibited. There are various signs on plants that are caused by a lack of lime. On closer inspection, they can also be seen by the untrained eye. In the case of a nutrient deficiency of calcium, the following signs can be observed on the plants, for example.
- weakened growth
- inhibited root formation
- light green or brownish spots on the leaves
- dry leaf edges (despite sufficient amounts of water)
- Bud rot in fruiting vegetables (such as peppers, cucumber, or tomato)
From a chemical point of view, lime is a compound of the element calcium. Calcium is one of the most important nutrients and mineral building blocks in plants. It is needed, for example, to build cell walls. In nature, calcium occurs in different rocks or sediments of the calcareous shells of mussels or snails as so-called "carbonate of lime". This is calcium carbonate (CaCO3). Many of the commercially available lime fertilizers are based on carbonate of lime.
In the trade, a wide variety of terms are used for garden lime. Similar raw materials are usually hidden behind the trade names. Depending on the type of soil, you can choose between different products.
In general it is recommended:
- Algae lime: for humus-rich soils
- carbonate of lime: for soil rich in humus
- Garden lime: for light and medium-heavy soils
- Lime marl: for very sandy soils
Quicklime (quicklime) and slaked lime
Quicklime or quicklime is calcium oxide that reacts with water to form so-called slaked lime (calcium hydroxide). Both forms work very quickly because they are in a highly water-soluble form. They are mainly used in agriculture. Both products are not recommended for private home gardens. These are very aggressive substances that not only can irreversibly corrode the skin and mucous membranes, but also damage plants and the environment if used improperly. It is better to use a mild version with calcium carbonate!
Carbonate of Lime (Natural Lime)
There are different types of lime that occur naturally as limestone, for example in chalk, dolomite lime, limestone or lime marl. The main component of these calcareous rocks is calcium carbonate, also known as carbonate of lime. Since this type of lime only dissolves slowly, it has a gentle and long-lasting effect. It is best applied in autumn. Dolomite lime also contains magnesium. The increased magnesium content is particularly suitable for plants with a high magnesium requirement, such as conifers. Anyone who limes regularly should not use any products with a magnesium content of more than 10%, otherwise there will be an oversupply.
Lime marl usually contains about 60 to 70% carbonate of lime. The rest consists of clay, which optimizes the storage capacity of very sandy soils. Lime marl also improves the soil quality in the long term because the clay content helps to stabilize the pH value.
Algae lime consists largely of calcium carbonate (around 70%), which is obtained from the dead deposits of red algae. In addition to calcium, it also contains magnesium (up to 10% magnesium carbonate) and various trace elements. However, algae lime is relatively expensive.algae lime
Garden lime/lawn lime
Depending on their use, various, mostly natural, lime products are referred to as garden lime or lawn lime. As a rule, these are variants of ground natural lime with a slightly lower magnesium content. Garden lime is usually used for light to medium garden soils in beds or for lawns. Since garden lime is naturally difficult to dissolve, it unfolds its effect slowly and gently. Basically, garden lime does not differ from lawn lime and both products can be used anywhere, provided they do not contain any additives such as weed killers or targeted fertilizers.
Rock flour, even primary rock flour, can vary greatly in its composition. While some products contain primarily calcium carbonate, magnesium, potassium and some trace elements, others have a high proportion of acidic components. It is therefore necessary to check in each individual case whether the rock flour is suitable for liming the garden soil at all.
Combination of lime and fertilizer
In addition, there are a variety of products that contain various additional fertilizers in addition to the actual garden lime. Most types of lawn lime are lime fertilizers that contain specific long-term fertilizers for grasses, for example.
time to deploy
The timing of applying the lime is also an important factor. The perfect season for liming flower and vegetable beds is spring or autumn. However, as calcareous products should not be applied together with nitrogenous fertilizers, as this leads to nitrogen losses, autumn liming makes more sense in most cases. Mild calcium carbonate products can be applied as lawn lime all year round if this should be necessary. It is best to whitewash the lawn after you have scarified it.
There are a few conditions you should keep in mind when applying garden lime to the beds or lawn. This includes that the garden lime should be distributed as widely and evenly as possible on the garden soil or the lawn.
- only lime when the soil is dry
- encrusted when in contact with rain or moisture
- Work deep into the soil on beds
- In the case of lawns, work it into the soil with a rake
- Do not use immediately after sowing lawn seed
- If possible, do not sprinkle over the plants (leaves, flowers and shoots).
- the use of some products causes burns to the plants
Determine lime requirement
If the pH value has been determined by means of a soil analysis, the lime requirement can be determined depending on the type of soil. Depending on how much the measured value deviates from the optimal value, liming the soil is more or less important and urgent.
The following applies:
- if there are deviations of more than 1.0 pH unit: liming has top priority
- with deviations of about 0.5: the liming takes place in the crop rotation
- with deviations of less than 0.3: small deviation, only lime fastidious plants
- slight upward deviations: no liming
- in the case of clear deviations upwards (pH value over 0.5 higher than desired): possibly acidic fertilization for sensitive plants
Since not every product contains the same ingredients, the content of CaO (calcium oxide) is always indicated on the packaging. We have created the following table for you so that you do not have to carry out complex calculations before applying the garden lime. Since most commercially available products contain around 60% or 80% CaO, the required quantities per square meter are given for both contents.
There are a number of crops that are somewhat sensitive to fresh lime in the vegetable patch. These should only be planted again on the bed if at least one lime-tolerant plant species has been planted beforehand. For this reason, you should never treat all the vegetable beds at the same time, but only if the rotation of the crop rotation provides for lime-tolerant plants.
Insensitive to fresh liming:
- all types of cabbage
- Lamb's lettuce