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Increasingly, garden owners are switching to organic products, especially when it comes to fertilizers. Relatively new in the range is algae lime. This is a purely natural product that supports natural planting. You can find out how algae lime works, where and how it should be used and other information worth knowing from Plantopedia.

algae lime

What is algae lime?

Algae lime is a natural raw material consisting of crushed deposits of red algae. It has a calcium carbonate content of around 80 percent and is therefore significantly higher than other lime fertilizers. As a purely ecological and biodegradable substance, it contributes to soil improvement and is not only used as a fertilizer, but is also used as a plant protection agent.

calcium carbonate

The contained calcium carbonate is one of the most common compounds that occur on earth. These connections are found in particular in sediments and sedimentary rocks, which are caused by the prevailing gravity on earth or flowing influences such as those found in the sea. Limescale deposits are mainly formed from organic, mineral residues, such as those that occur on corals, mussels or red algae as these deposits and ensure an alkaline environment.


Algae lime fertilizer: Applications in the garden - Boxwood & Co

Fertilizer makes a significant contribution to healthy plant growth. The basis for this lies in the soil quality or composition. Numerous diseases develop when the soil does not meet the requirements of the respective plant. If there is a lack of lime, brown leaves can develop on a boxwood, for example. Lime is an important fertilizer here, helping to improve the soil. You should know whether and how algae lime helps and when it is useful before you use it.


Just as calcium carbonate creates an alkaline environment from the separation of sediments and/or sedimentary rocks, the same effect can be seen in the soil after fertilization. This type of lime leads to a neutralization of the soil acid content (pH value) and thus prevents a mostly gradual soil acidification or reduces the acidic soil conditions.


There is a spontaneous, rich release of nutrients, although humus is broken down at the same time, which is why the dosage of algae lime should always be moderate.

In addition, the high calcium carbonate content in conjunction with other ingredients causes the transformation of small clay particles into larger crumbs, resulting in improved water and air retention. In a biological way, this fertilizer activates microorganisms and as a result, improving the structure of the soil and reducing siltation, the soil can warm up faster, thus favoring the growth of microorganisms and consequently plants.

Lime-loving plants

In the plant world, a distinction is made between lime-loving specimens and plants that do not tolerate lime. Especially with plants that are sensitive to lime, the high-dose calcium carbonate fertilizer should not be used.

Plants that tolerate lime include:

  • lilac
  • lavender
  • christmas roses
  • boxwood
  • Judas tree
  • smoke bushes
  • common ash
  • tulip roses
  • sea buckthorn and blackthorn
  • daisies
  • lawn/grass
  • many herbs such as parsley, chives, wild garlic
  • and many more

lack of lime

A lime deficiency can be recognized quite quickly in plants that prefer a calcareous soil composition or that thrive better with the addition of lime.

Typical features can be shown, among other things, in the form of:

  • blossom end rot (tomato)
  • growth disorders
  • dried shoot tips
  • Yellowing of new/young leaves
  • brown dots on fruit peels (e.g. apples)

You can also tell whether your soil needs algae lime from the so-called indicator plants. If the lime content is too low, these plants will quickly indicate it, so that you can act quickly.

Examples include the following plants:

  • rabbit clover
  • moss
  • Little sorrel
  • Sand Pansies
  • field horsetail
  • Three Leaf Prize
  • peasant mustard


In general, this particular type of lime shows itself in several directions with beneficial properties for the soil/plants, compared to other types of lime for garden fertilization

  • containing more trace elements
  • more favorable ratio between lime and contained magnesium
  • improves the availability of nutrients and ensures biologically active soil conditions
  • particularly high effectiveness due to high calcium carbonate content
  • can be fertilized all year round
  • prevents fungal attack by lime pollination of the plant
  • keeps insects at a distance after lime pollination
  • ensures more flavor intensity and durability of herbs, fruit and fruits
  • Binds soil acids much better due to the high calcium carbonate content
  • Strengthens plants and promotes resistance to disease and pest infestation


When to use algae lime fertilizer?

The pH value of a soil shows how acidic it is. This is influenced by the different soil types. A certain pH value is partly responsible for the growth of every plant species and should therefore always be within a certain range. Over time, the acidity often moves towards higher values towards becoming more acidic. Then the addition of algae lime fertilizer is useful to bring about regulation.

You can use the different types of soil and the ideal pH values as a guide:

  • Loess and clay soil: pH value 7.0
  • Sandy loam soil: pH 6.5
  • Clay sandy soil: pH 6.0
  • Sandy soil: pH 5.5

For lawns, depending on the type of soil, the pH value should be less than 0.5 less than the ideal pH value for the individual soil types. If moss has formed on the lawn, this is a clear sign of a lack of lime in the soil. But don't forget that there are plants that do not tolerate calcareous soil. These include, for example, rhododendrons, summer heather, hydrangeas and ericaceous plants.


Dosing instructions are usually given on the packaging of algae lime fertilizer. This usually refers to a general quantity, without reference to the prevailing soil conditions or soil type and pH values. Algae lime fertilizers are often advertised with the comment "for healthy soils". Here it can be assumed that, according to the manufacturer's recommendation, the mostly lower amounts of lime should prevent acidification as a precaution. The dosage recommendations are usually less useful for treating pH values that are already too high/acidic. So it can happen that the dosage information given by the manufacturer may not be optimal for your soil.


If there is too much lime fertilization, chemical processes can be triggered, especially in loamy soils, which in the worst case can cause irreparable damage to your plants and massive nutrients are broken down in the soil, which are then no longer available to the plants. Too little algae lime fertilizer means you have to wait in vain for an effect.

  • Dosing for pH reduction

You should stick to the following dosage based on the soil conditions.

  • Light soils with a pH lower than 5.3: 150 to 200 grams of lime per square meter
  • Light soils with pH between 5.3 - 5.7: 120 to 180 grams of lime per square meter
  • Medium-heavy soils with a pH lower than 5.7: 300 to 400 grams of lime per square meter
  • Medium-heavy soils with a pH between 5.7 and 6.5: 180 to 250 grams of lime per square meter
  • Heavy soils with a pH lower than 6.3: 400 grams of lime per square meter
  • Heavy soils with pH between 6.3 - 7.0: 250 to 350 grams of lime per square meter

TIP: You can buy cheap test strips to determine the pH value. You should make this investment in order to be able to choose an optimal dosage. Special electrical measuring devices are easier to use, but are also more expensive.


In general, before using algae lime in the garden, you should know that some of it can fly through the air like powder, especially in windy conditions. It can irritate the eyes and cause health reactions in allergy sufferers and asthmatics. Even small children should not come into contact with the powder.


The most important criterion when fertilizing algae lime is the even application. Only in this way can you distribute the optimal dosage over the smallest areas and avoid over- or under-dosing.

Large-scale fertilization

For larger areas, fertilizing with a fertilizer wagon is recommended. This has opening slits, which usually allow optimal adjustment of the dosage. The prerequisite is that the opening slits are not blocked, for example by lumps in the fertilizer, which can occur due to moisture or production errors. It is therefore advisable to check for lumps when filling in the fertilizer.

Small-scale fertilization

On small areas or, for example, under boxwood bushes and between rose beds, this lime fertilizer can often only be spread by hand or with a shovel. Here it is advisable to separate the exact dose per square meter and sprinkle the lightly granular powder square by square meter with your hand/scoop. This will ensure you spread the recommended dose evenly over the area.


fertilizer combinations

Algae lime fertilizer does not always have to be applied pure to the area to be fertilized. When added to compost, it works very effectively. This also has the advantage that the soil is simultaneously enriched with additional nutrients from the compost and are better absorbed by the plant due to the algae lime.

Notice: Always wear gloves when fertilizing. The high dose of calcium carbonate can cause skin irritation. In the event of skin or eye contact, it is essential to rinse the affected area with plenty of clean water.

time of fertilization

The best time to apply algae lime in the garden is in the spring, although it can also be used all year round as needed. The soil should be slightly damp but not too wet. This ensures better adhesion of the powder. Especially if you distribute the fertilizer by hand, you are dependent on the sifting to prevent double fertilizer application. If the soil is too wet, it would dissolve very quickly and would no longer be visible.

If you fertilize a lawn with a fertilizer wagon, the tracks on the wet ground could provoke unsightly ruts and possibly damage the turf.

It is advisable to choose a dry day for fertilizing when rain is imminent. If it rains after fertilizing, the lime quickly soaks into the soil. If there is no watering, the fine powder in particular can be carried away by the wind and stick under shoes, which is why fertilized areas should not be walked on until watered. If there is no rain, we recommend watering box trees and the like after fertilizing and/or turning on the garden sprinkler.


Algae lime is offered in a wide variety of price ranges. When it comes to higher-priced red algae lime fertilizers, manufacturers usually argue that they are significantly purer thanks to special cleaning processes. It has not yet been scientifically proven that this would improve the positive properties of this type of lime. Normal garden lime with calcium carbonate costs around 80 cents per kilogram on average. For chalky lime or E170 you usually have to reckon with several euros per kilogram.

The prices for algae lime range from 1.25 euros to over 23 euros per kilogram. Here it mostly depends on whether the lime comes from wild red algae or from “ordinary” seaweed. There is also algae lime as a dietary supplement for dogs. These usually contain lime from the Lithothamnium algae. This can also be safely used for lime fertilization in the garden.

Here is a small overview of manufacturers and prices of algae lime:

  • Cohrs - 25 kilograms for 25.50 euros plus shipping costs
  • Cohrs - five kilograms for 18.37 euros
  • ManuFACTUM - five kilograms of seaweed for 16 euros plus shipping costs
  • - 500 grams for 9.48 euros

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