Most Common Types of Algae Used as Fertilizer

As growers, we are always looking for more sustainable ways to improve our soil health and enhance crop output. Algae-based fertilizers have moved from niche to much more common over the past few years. However, understanding which type of algae is most beneficial for your soil and crop is crucial to getting the most out of it. 

Seaweed Algae Fertilizers (Macroalgae)

Seaweed-based fertilizers, or sometimes called kelp fertilizers come from large marine algae and have been used in agriculture for centuries. They deliver a wide spectrum of natural compounds that go beyond basic NPK nutrition. Most seaweed products are applied as a foliar spray or through irrigation systems, so they’re easy to work into whatever program you’re already running.

Ascophyllum nodosum (Brown Seaweed)

If you’ve done any research into seaweed fertilizers, you’ve probably come across Ascophyllum nodosum. It’s harvested from cold North Atlantic waters and is about as close to a gold standard as you’ll find in this category. 

Ascophyllum nodosum is a type of brown seaweed that is sometimes called Norwegian kelp or rockweed. It’s the main, high-quality source used to make what we know as kelp meal. Technically, kelp meal could come from other seaweeds, but just about every ag product labeled “kelp meal” is made from Ascophyllum nodosum. If you’re buying kelp for your farm, chances are that’s what you’re getting.

Research has shown proven benefits to multiple species of plants. What makes it stand out is its natural plant hormone content, especially auxins and cytokinins.

Auxins → support root initiation and elongation

Cytokinins → promote cell division and delay leaf aging

Gibberellins → stimulate growth

Alginates → improve soil structure and water retention

Trace minerals → support balanced plant nutrition

For growers dealing with heat stress, drought, or frost pressure, this is one of the first products we reach for.

Laminaria spp. (True Kelp)

Kelp is a loosely used term in agriculture, but biologists would call Laminaria species kelp as opposed to seaweed. This is another well-researched macroalgae with a strong track record across many crop types. Like Ascophyllum, it’s loaded with auxins and cytokinins that push root development and early growth. Where kelp really shines is during transplanting or crop establishment, when plants need to get their roots down fast and recover quickly from the stress of being moved.

Using a liquid fertilizer like Seastim is a great way to get the benefits of kelp onto your plants quickly and begin building stronger roots. 

Sargassum Species

Sargassum is a brown macroalgae you’ll see more often in programs running in warmer, tropical, or subtropical growing regions. It carries the same core benefits as other seaweeds, including amino acids, trace minerals, and natural plant hormones, but it tends to do especially well at supporting the microbial communities around the root zone. For growers who are focused on soil biology as much as plant nutrition, Sargassum can be a strong complement to your broader biological program.

Microalgae & Cyanobacteria (Blue-Green Algae)

Where macroalgae is harvested from the ocean, microalgae are microscopic single-celled organisms that bring a different and highly concentrated set of benefits to the soil. One thing worth knowing is that cyanobacteria, often called blue-green algae, are technically bacteria rather than true algae. They get grouped in with microalgae in fertilization conversations because they function similarly when it comes to building soil health.

Chlorella

Chlorella is one of the most studied microalgae for agricultural use, and for good reason. It’s packed with proteins, amino acids, organic carbon, and natural growth stimulants that feed both your plants and your soil microbiome at the same time. When you apply it to soil, you can expect improvements in microbial diversity, nutrient cycling, soil organic matter, and root-zone biology.

One strain in particular, Chlorella vulgaris, has shown exceptional results for soil regeneration and crop growth. That’s why products built around live-cell Chlorella vulgaris, such as EnSoil Algae, are gaining traction among regenerative growers.

Spirulina (Arthrospira)

Spirulina is technically a cyanobacterium, which puts it in the blue-green algae family, but it’s almost always grouped alongside microalgae because of how it grows and how it performs in the field. It’s extremely protein-dense and brings a wide profile of amino acids, micronutrients, and pigments that support both plant health and soil vitality. As a compost amendment or component in a biological inoculant blend, spirulina contributes organic carbon and gets beneficial microbial populations working harder.

Which Type of Algae is Right For Your Soil?

Algae products are not magic solutions on their own. Their real value shows up when they are part of a balanced fertility program built around soil testing, mineral balance, and active biology.

It is unlikely that adding algae to your soil will harm your crops in any way, but you could be wasting resources adding amendments your soil and crops don’t actually need. We encourage all of our growers to conduct a soil test to understand what nutrients their soil is lacking. We also offer regenerative consulting where our consultants will evaluate your soil health and your crop health and put a nutrient management program into place to ensure you are adding the necessary amendments to grow the healthiest crop possible. 

Contact Keystone Bio-Ag today to learn more about our products, or get started on a soil treatment plan for your farm.