Ascophyllum, Sargassum, Kappaphycus: what is the difference?

Ascophyllum and Sargassum are brown seaweeds. Kappaphycus is a red seaweed. They grow in different places and contain different main sugars: alginate and fucoidan in brown, carrageenan in red. Studies report benefits from all three in different crops, so no species is best on paper. Choose by crop, stage, purpose, extraction and your own trial.

Updated 2026-11-09

See also: Plant Science Series and the Immunity range.

A label may say Ascophyllum, Sargassum or Kappaphycus, and a seller may tell you his species is the one to buy. This page sets out what is really known about the three, and how to use that when you choose.

Brown seaweed or red seaweed

Ascophyllum and Sargassum are brown seaweeds. Kappaphycus is a red seaweed. The group matters because it decides the main sugars in the plant. One review reports that brown seaweeds contain 17 to 45% alginates and 5 to 20% fucoidan, along with laminarin. Red seaweeds contain carrageenans instead. In India, Kappaphycus is farmed mainly as a source of kappa carrageenan.

The same review says the type and amount of these sugars depend on the species and on where it grew, and change with the season. So two batches of one species can also differ.

The three side by side

Sources for the table: Ascophyllum review, CMFRI 2023, CMFRI 2011, CMFRI on Sargassum, CMFRI resource review.

What studies report for each

Ascophyllum. A review of Ascophyllum products lists alginic acid at 28%, fucoidans at 11.6%, mannitol at 7.5% and laminarin at 4.5%, and reports betaines such as glycine betaine in the extract. It reports that foliar sprays improved fruit quality in watermelon, apple, olive and grape. It also reports less drought stress in soybean and bean, and better salt tolerance in tomato.

Sargassum. A wider review lists Sargassum extracts among those that increased tolerance to salt and drought in tomato and sweet pepper. In India, the most useful study for a Gujarat reader was done at CSMCRI, Bhavnagar, and is described below.

Kappaphycus. The same review describes improved drought and salt tolerance in wheat and drought tolerance in soybean. In a two-season rice trial at Ranchi, Jharkhand, the crop sprayed with Kappaphycus sap gave more grains per panicle, and the most productive treatment also received the full recommended fertiliser dose. In a maize trial in Meghalaya, Kappaphycus sap and sap of another red seaweed, Gracilaria, performed at a similar level as foliar sprays.

These are results for particular extracts, crops and places. They do not tell you what any product on the shop shelf will do on your farm.

Why no species wins on paper

The studies to look at are the ones that test species together, in one crop, in one place. Two of them show the problem.

In a pot study at CSMCRI, Bhavnagar, maize was sprayed with simple Kappaphycus and Sargassum preparations, alone and in blends. Sargassum alone gave the highest seed yield at the lower dose, but Kappaphycus alone at the lower dose was on par with it. Some blends were comparable. The best response was generally at the lower dose, and the highest Sargassum dose was on par with no spray at all. This was one hybrid in one rabi season in a net house, so it is not a rule for field crops.

In a 2025 tomato trial, Sargassum extract gave the highest fruit Brix and Ascophyllum extract the highest proline, a compound linked to plant stress response. A commercial Ascophyllum extract showed lower proline than the other preparations. So one species gave different results depending on how it was prepared.

Extraction can change what you are buying

The Ascophyllum review says composition and activity depend on the extraction method. Alkaline extraction breaks long sugars into smaller pieces and can produce compounds that were not in the seaweed. Acid treatment removes some phenolic compounds. Another review says alkaline extraction at high pressure is the most widely used process and has been found effective, although some hormone-like molecules can be degraded.

At our own plant at GIDC Shihor, Bhavnagar, we extract seaweed in-house by a mild method, without harsh chemicals, very high pH or heat. That is our choice of process. It does not excuse any product, ours included, from a fair trial on your farm.

How to choose

• Write your purpose first. Roots after transplanting, stress before a dry spell, or flowering are different jobs. Note the crop and the stage.
• Look for the species name. "Seaweed extract" alone tells you little. Ask for the species in full.
• Ask how it was extracted and where the raw material came from. A seller who cannot answer has not earned your money.
• Ask for batch details. Our quality page shows the kind of checks to ask any supplier about.
• Compare the cost per spray at the dose on each pack, not the price per litre.
• Be careful with "best". Any claim that one species is best for all crops goes beyond what the studies show.

Test two products side by side

Choose one uniform block with the same variety, fertiliser and irrigation. Make three strips: product A, product B, and one with no spray. Spray A and B on the same day, each at the dose on its own pack. Mark the strips. Then measure what you bought it for: root mass after two to three weeks, flower or fruit count, or final yield from each strip. Write down dates and weather. Repeat next season before you change your buying, because one season can mislead. Results vary by soil, variety and region.

If you want to understand how these compounds act inside the plant, read our plant science series.

What not to do

• Do not mix all three species hoping for more. In the Bhavnagar pot study, blends were comparable to single species, not better.
• Do not raise the dose above the pack. A higher dose was not better in that study.
• Do not soak seed in a stronger solution than the label says. In the Meghalaya trial, higher sap concentrations reduced maize germination and root length.
• Do not copy a dose from a research paper. Those doses were for that sap, in that trial.
• Do not cut your fertiliser because you are spraying seaweed.

If you want help comparing two labels, send us a photo of both, with your crop, its stage and what you want the spray to do, on +91 99787 91167 (call or WhatsApp) or sales@gujaratbio.com.

Sources

• Ali, Ramsubhag and Jayaraman (2021). Biostimulant properties of seaweed extracts in plants. Plants 10(3):531
• Shukla et al. (2019). Ascophyllum nodosum-based biostimulants. Frontiers in Plant Science 10:655
• Vaghela et al. (2023). Maize response to minimally processed homogenates of red and brown seaweeds (CSMCRI). Frontiers in Plant Science 14
• Spagnuolo et al. (2025). Comparative effects of macroalgal extracts on tomato plant growth and fruit quality. Phycology 5(2):22
• Singh et al. (2015). Effect of fertilizer level and seaweed sap on productivity and profitability of rice. Indian Journal of Agronomy 60(3)
• Layek et al. (2016). Effect of seaweed sap on germination, growth and productivity of maize in North Eastern Himalayas. Indian Journal of Agronomy 61(3)
• Johnson et al. (2023). Seaweed farming technologies. ICAR-CMFRI
• Johnson and Gopakumar (2011). Farming of the seaweed Kappaphycus alvarezii in Tamil Nadu coast. CMFRI Marine Fisheries Information Service 208
• Kalimuthu et al. (1990). Present status of seaweed exploitation and seaweed industry in India. CMFRI Marine Fisheries Information Service 103
• Baby Ushakiran, Merlee Teresa and Kaladharan. A review on resources, cultivation and utilisation of marine macroalgae in India. CMFRI
• Johnson and Ignatius (2020). Seaweed farming in India: progress and prospects. Indian Farming 70(11)

By Gafar Laiya, founder of Gujarat Bio Organics, working with farmers since 2006. Results differ from farm to farm with soil, weather, crop and management. Farmer experiences on this site are their own reports, not a promise of results.