Lithothamnium is a natural marine amendment made from calcified seaweed. It comes from red coralline algae that build a hard skeleton of calcium and magnesium carbonate. Ground or granulated, it is used to correct soil acidity and to supply calcium and magnesium, and in suitable grades it also goes into animal feed and water treatment.
Agromer supplies lithothamnium alongside its DAP and organic fertilizer range, for distributors, blenders and commercial growers. This page explains what the product is, how it works and what to agree before you order.
What lithothamnium is
The name comes from *Lithothamnion*, one of the genera of red algae that form calcified deposits on the seabed. These deposits, also called maerl, build up slowly from the skeletons of the algae. The material sold for agriculture is dried, cleaned and then ground into powder or made into granules.
Its composition is mostly calcium carbonate, with a smaller share of magnesium carbonate and a range of trace elements from seawater. The exact figures vary with the deposit and the processing, so always work from the producer’s certificate of analysis for the lot you buy.
How it works in the soil
- Raises soil pH. Like other carbonate liming materials, lithothamnium neutralises soil acidity. Many crops grow poorly on acid soils, where phosphorus is locked up and aluminium and manganese can become toxic.
- Supplies calcium and magnesium. Both are major plant nutrients. Magnesium is at the centre of the chlorophyll molecule, and calcium is needed for cell walls and fruit quality.
- Reacts relatively quickly. The skeleton of the algae is porous, with a large surface area. For that reason calcified seaweed is often described as faster acting than many ground limestones of a similar particle size.
- Improves soil conditions for biology. Correcting pH helps earthworms and soil microbes, including the bacteria that fix nitrogen in legume roots.
Lithothamnium does not replace nitrogen, phosphate or potash. It is an amendment that makes the rest of the fertilizer programme work better on acid or calcium-poor soils.
Where it is used
| Use | Why |
|---|---|
| Acid arable and grassland soils | Corrects pH and supplies calcium and magnesium |
| Fruit and vegetables | Calcium supply, for example where calcium disorders are a concern |
| Organic farming | A natural mineral amendment; approval depends on the certifier and market |
| Compost and growing media | Buffers acidity |
| Animal feed | Feed-grade material as a mineral source |
| Water treatment and fish farming | Buffers acidity in water, in suitable grades |
Lithothamnium vs ground limestone
Both are carbonate liming materials. Ground limestone is mined on land and is usually cheaper per tonne. Lithothamnium is chosen for its magnesium and trace elements, its porous structure and, in organic systems, its natural marine origin. Which one makes sense depends on soil analysis, the crop, the price delivered to your farm and the rate you need.
Sourcing and sustainability
Maerl beds grow very slowly and are important marine habitats. In Europe, the main maerl-forming species are listed under EU nature law, and harvesting is regulated. Responsible supply comes from licensed operations, and buyers should expect to see where the material comes from. Ask your supplier for the origin and the relevant permits.
What to check before you buy
- Analysis: calcium carbonate and magnesium carbonate content, moisture and neutralising value.
- Form and particle size: fine powder, micro-granules or granules, to suit your spreader or blending plant.
- Grade: agricultural, feed or water treatment.
- Origin and permits: where it was harvested and under what licence.
- Certification: organic input approval, if your market needs it.
- Packaging: bulk, big bags or bags, and quantity.
- Delivery: destination port and Incoterm.
Our guide to requesting a bulk commodity quotation shows how to set out an enquiry so suppliers can price it quickly.
Lithothamnium from Agromer
Agromer has traded agricultural commodities internationally since 1985 from Saint-Avertin, France. We supply lithothamnium as a marine calcareous amendment, together with organic fertilizers such as manure pellets, liquid biofertilizers and blood and bone fertilizer. We trade with businesses only, in bulk shipments, and payment is by documentary letter of credit or SBLC.
Frequently asked questions
What is lithothamnium?
Lithothamnium is calcified seaweed: the hard skeletons of red coralline algae, made up mostly of calcium carbonate with magnesium carbonate and trace elements. It is dried and ground for use as a soil amendment.
What is lithothamnium used for?
Mainly to raise the pH of acid soils and to supply calcium and magnesium. Suitable grades are also used in animal feed, compost, growing media and water treatment.
Is lithothamnium a fertilizer?
It is better described as a soil amendment. It supplies calcium and magnesium and corrects acidity, but it does not provide significant nitrogen, phosphate or potash.
Is calcified seaweed allowed in organic farming?
It is a natural mineral product and is widely used in organic systems, but approval depends on your certifier and country. Tell us which certificate you need and we confirm what is available in the offer.
What is the difference between lithothamnium and limestone?
Both neutralise acidity. Lithothamnium is porous and contains magnesium and trace elements; limestone is usually cheaper per tonne. Soil analysis and delivered price decide which suits your farm.
Does Agromer supply small quantities?
No. Agromer supplies businesses in bulk shipments only, not retail or small farm quantities.