What Is Sapropel?
Sapropel is an organic-rich sediment that forms naturally at the bottom of freshwater lakes over thousands of years, from the slow accumulation and partial decomposition of plant matter, algae and minerals. It is the raw material behind BioAktiva’s registered SaproGro™ liquid fertiliser and HumiGro™ peat blend — both derived from sapropel sourced from freshwater lakes in the Baltic region.
How sapropel forms
Sapropel accumulates on lake beds over very long timescales — typically thousands of years — as plant material, plankton and waterborne minerals settle, layer, and slowly break down in a low-oxygen environment. This slow, low-oxygen decomposition is what distinguishes sapropel from surface compost or fast-cycling organic matter: the process concentrates organic compounds and minerals gradually, rather than breaking them down quickly the way aerobic composting does.
Because it forms underwater, sapropel is a fundamentally different material from peat, which typically forms in above-water or waterlogged bog conditions from plant matter dominated by cellulose and lignin.
What sapropel naturally contains
Sapropel’s composition varies by source lake, but it typically carries three broad components:
- Organic substances — including humic acids, carbohydrates and natural colloids formed during the decomposition process.
- Water-soluble organic and mineral substances — compounds that are already in a form plants and soil can readily interact with.
- Mineral substances — a broad profile of macro and microelements, including silicon, calcium, aluminium and iron, alongside trace elements.
BioAktiva’s registered SaproGro™ liquid fertiliser (Act 36 of 1947, Reg. No. B6628) is derived from this material and carries a guaranteed analysis of Nitrogen (N) 60 g/kg, Potassium (K) 8.5 g/kg, Calcium (Ca) 8.5 g/kg and Iron (Fe) 60 mg/kg, at a specific gravity of 1.05 at 20°C. See the full label directions for registered application rates.
Sapropel vs. other organic soil inputs
Sapropel is often grouped with other organic amendments — peat, seaweed extracts, and lignite-derived (leonardite) products — but the raw materials and how they form are genuinely different:
- Peat forms above or at the waterline from cellulose- and lignin-heavy plant matter, and is typically more acidic.
- Seaweed extracts are derived from harvested marine macroalgae, processed to extract specific compounds.
- Leonardite (lignite-derived) products come from a mined mineral — oxidised lignite — rather than a naturally forming freshwater sediment.
- Sapropel forms underwater in freshwater lakes, from a mixed accumulation of plant, plankton and mineral material, over a much longer and slower process than any of the above.
A full side-by-side comparison of typical dosage and application is on our SaproGro comparison table.
Where BioAktiva’s sapropel comes from
BioAktiva’s sapropel is sourced from freshwater lakes in the Baltic region and manufactured to specification for the South African market. Both SaproGro™ (liquid fertiliser) and HumiGro™ (a Baltic peat product blended with a small proportion of sapropel) are registered under Act 36 of 1947 for use in South Africa — SaproGro as Reg. No. B6628, HumiGro as Reg. No. B6777.
Frequently asked questions
Is sapropel organic?
Sapropel is a naturally occurring organic sediment, not a synthetic or manufactured blend. SaproGro™, derived from it, is registered in South Africa as a Group 2 organic liquid fertiliser.
Is sapropel the same as pond mud or sludge?
Sapropel is a specific type of lake sediment with a distinct composition profile, formed over thousands of years through a defined natural process. It is not general pond sludge or dredged waste material.
What’s the difference between sapropel and peat?
Both are organic sediments, but they form in different conditions and from different source material. Peat forms above or at the waterline from cellulose- and lignin-dominant plant matter and tends to be more acidic. Sapropel forms fully underwater from a mixed accumulation of plant, plankton and mineral material. HumiGro™ combines milled Baltic peat with a smaller proportion of sapropel as an additive.
Can sapropel-based products be used alongside other fertilisers?
Always follow the specific product’s registered label directions. See SaproGro’s label directions for registered application rates and compatibility notes.
Where can I buy sapropel-based fertiliser in South Africa?
SaproGro™ liquid fertiliser is available in 1 L, 5 L and 20 L sizes, and HumiGro™ peat is supplied to trade in bulk. Shop SaproGro™ or apply for a trade account for HumiGro™ pricing.
SaproGro™ is a registered Group 2 organic liquid fertiliser (Act 36 of 1947, Reg. No. B6628). HumiGro™ is a registered Group 2 organic peat product (Act 36 of 1947, Reg. No. B6777). Always use according to approved label directions.