Seaweed Fertilizer: Does Organic Matter?


I’m just going to come out and say it: seaweed is awesome. You may not spend much of your daily life thinking about seaweed, but as a writer and a kelp enthusiast (yes, it’s a thing), I feel summoned to elevate awareness for this marine vegetable, to make a case for its place in our lives, and to urge future seaweed worshippers (have I gone too far?) to think holistically about the products they consume.

As a marine algae, seaweed is not inhibited by gravity in the same way that its terrestrial relatives are. For this reason, kelp and other seaweeds are some of the fastest growing algae in the world, with a species of giant kelp, Macrocystis pyrifera (I think the Latin names have a kind of melody to them), growing up to two feet in a single day. Which, needless to say, is crazy. It’s like a real-life time lapse!


Life In Liquid: Super Seaweed

Their liquid habitat also means that they don’t collect nutrients from soil via roots, but directly from the water through their tissue. Seaweed absorbs all kinds of minerals and vitamins from the ocean, giving seaweed and seaweed products some amazing health properties for humans, and growth properties for gardens when used as fertilizer.

And that’s not all: seaweed is also an incredible sink for carbon and producer of oxygen. It has been estimated that seaweed alone sequesters 634 million tons of carbon per year, which is more carbon than is produced by Australia. You know, the country. Likewise, seaweed and phytoplankton (its microscopic cousin), are responsible for up to 90% of the oxygen in the atmosphere. So next time you take a breath, think about sending a little “thank you” to those ocean greens.

All of these magnificent properties have captured the attention of environmentalists and scientists around the world, as well as businesses. Seaweed is a marine vegetable that can be consumed, used in pharmaceuticals, beauty products, as a fertilizer, in animal feed, and even as a biofuel. All of these applications for seaweed make it seem pretty appealing, especially if you factor in that growing (or harvesting wild) seaweed doesn’t require soil, fertilizer, or freshwater: it just grows.

Does Organic Matter?

Now that you’ve joined me on the seaweed bandwagon (welcome), let’s talk specifically about its role as a fertilizer. Seaweed is used as fertilizer, most often in liquid form, because of its beneficial effects on plants and soil. According to the USDA, “the high fiber content of the seaweed acts as a soil conditioner and assists moisture retention, while the mineral content is a useful fertilizer and source of trace elements.” So it’s great food for, well, your food, but does it matter if it’s organic?

The short answer: yes. The long answer: it’s complicated. The organic certification is basically a yearly check that all parts of the seaweed-harvesting and production process are safe and sustainable. I will argue that the sustainability aspect of the certification is perhaps the most important part. Not because I don’t care about your health (I work for an organic food company, have some faith), but because the laws and practices surrounding the harvesting of this marine deity are somewhat fractured, and stronger in some areas than others.

In the (sea)weeds…

Let’s start at the beginning. If you wanted to grow or harvest seaweed in coastal waters or in the rocky intertidal zone (the shore), you’d need a permit. That’s because this land and these waters are public, and therefore subject to local, state and federal laws that are actually pretty strict about what you can and can’t take, and from where. For example, the State of Maine prohibits the cultivation of any aquaculture (seaweed included) in the area surrounding Portland, their major coastal city, due to poor water quality. Additionally, each of the plots that are leased to ocean farmers (as of now, citizens cannot purchase parts of the ocean), go through a lengthy application process that includes environmental assessments and public hearings. In fact, there is some pushback, particularly on the west coast, that government regulations are stifling the would-be-booming seaweed farming industry.

seaweed farm.jpg

Salty Certification

Now for the organic certification piece. The rules for organic certification were written with terrestrial farming in mind, which means there are a few holes and contradictions when it comes to marine harvesting - ask the USDA, they said so themselves. For example, livestock is only considered organic if it is fed organic certified seaweed, while farmers may grow organic-certified crops using non-organic seaweed fertilizer. In addition, the organic certification is very vague when it comes to supporting the sustainability of seaweed harvest, stating that “production practices must maintain or improve the natural resources of an operation under organic certification”. Though a good sentiment, there are many ways to measure this requirement, and the organic certifiers are left to do some interpreting of their own. For example, one certifier requires that seaweed spores be regularly taken from wild populations to maintain genetic diversity in the cultivated populations - an excellent environmental practice.

That said, what the certification process does cover, which public laws do not, is the handling and processing of seaweed. Organic certified seaweeds may not have any chemicals or fertilizers applied throughout the growing process, which, for many seaweed farms, includes a spore germination phase conducted in an on-shore laboratory.

Seaweed Summary

Given all of this information, I’m left with a few takeaways. First, seaweed is amazing and we should all use it for everything. Second, we’re only really just beginning to understand how to responsibly harvest seaweed in America, and our laws are struggling to catch up with the increase in seaweed demand while incorporating our ever-evolving scientific understanding of seaweed ecosystems, which, as we’ve learned, are super important for the health of the planet. I look at the organic certification as a message to the industry that consumers care about where their seaweed is harvested from, that it protects the environment, and of course our health.

Louisa Pitney