Seaweed has been used by coastal populations for generations and for good reason! It was plentiful, easily accessible, and most importantly, gave great results. As modern fertilizers became more commonplace, seaweed lost its appeal and luster. But some farmers and avid gardeners kept the tradition alive and science is finally catching up. So, let’s take a deep dive into seaweed fertilizers and how you can use them for your plants.
What is seaweed fertilizer?
As the name suggests, seaweed fertilizer is fertilizer made from seaweed. There are generally 3 forms of seaweed products: liquids, soluble powders and meals. The liquid extracts and soluble powders are diluted with water and used to water plants. The meals, or granulated seaweed is applied to the soil. Although the specific species of seaweed used in each fertilizer isn’t always specified, most are made of kelp.
Seaweed is the common name used to refer to algae that grow in salt or fresh water. There are three main groups of seaweed: red algae (Rhodophyta), green algae (Chlorophyta), and brown algae (Phaeophyceae). Each species of seaweed has a different nutrient composition.
Fun fact: red and green algae are more closely related to land plants than they are to brown algae.
Why use seaweed fertilizer?
Seaweed has many benefits for plants and soil. First, it is an excellent vegan source of minerals (including trace minerals), vitamins, and amino acids. These are all essential nutrients for plant growth. In fact, seaweeds have 10 to 20 times more minerals than plants grown in soil 1 ; 4 .
Seaweeds also have different diseases that cannot be transferred to land plants, which can be a common problem when composting infected plant material.
Dry seaweed can help improve soil texture by adding organic matter and increasing water retention. It also encourages microbial activity and diversity.
Finally, seaweed is a biostimulant for plants. A biostimulant is a substance that acts on the plant’s metabolism independent of the nutrients it may provide. Biostimulants can make plants more resilient to stressors like extreme weather or pests and improve growth.
What is a biostimulant?
A biostimulant is a substance that acts on an organism’s metabolism regardless of the nutrients it contains. For plants, this means a biostimulant could have no NPK but still affect growth and resilience. Instead, they act on the phytohormones (plant hormones) that regulate the plant’s metabolism.
There are many kinds of biostimulants already used in agriculture and home gardening. Some common ones are seaweed, insect frass (insect manure) and myccorhizae.
With all that in mind, what is Seafeed and how does it compare to other forms of seaweed fertilizer?
What is Seafeed?
Seafeed is a seaweed plant biostimulant, made from 4 main types of seaweed.
We refer to it as a biostimulant instead of a fertilizer because it does not provide enough nitrogen, phosphorus, and potassium for plants. The real benefit comes from the micronutrients.
How is Seafeed made?
In many aspects, Seafeed still reflects the traditional of seaweed collection methods. Our seaweed is collected by hand after storms when fresh seaweed piles along the beaches of Prince Edward Island (PEI). We use the natural mix of seaweeds that washes ashore, mainly composed of Furcellaria lumbricalis (Furcellaria or called “Fufu” in PEI), Chondrus crispus (Irish moss), Fucus vesiculosus (called both bladderwrack and rockweed depending on which region you are in) and Laminaraceae sp. (kelp species).
Traditionally in PEI, seaweed was collected with the help of draft horses that would brave the waves. But, now, the less temperamental truck is used. It is then laid out in fields to sun-dry before being brought to our facility where it is sorted and crushed.
This process means we are uniquely in tune with the weather. We are constantly assessing winds, ocean currents, temperature, and cloud cover to time collection and drying. Head over here for the story of how we got started.
The natural blend of seaweed is roughly composed of 75% red algae (Furcellaria and Irish moss) and 25% brown algae (bladderwrack and kelp). Furcellaria and Irish moss live below the bladderwrack on shallow rocky shelves. The red algae we use are not cultivated because these habitat conditions are complicated to replicate.
What about kelp fertilizer?
Are kelp and seaweed the same thing?
Kelp is a type of seaweed, brown seaweed more specifically. Kelp fertilizers are generally made from a single species of kelp. On the eastern coast of Canada it is Ascophyllum nodosum. The lack of diversity in seaweed fertilizers comes from the production methods.
So how are kelp fertilizers made?
Compared to red algae, kelp is relatively easy to cultivate. Kelp spores (tiny cells that grow into kelp) are placed onto grow lines that are strung in the water. It is grown over winter and harvested in spring, then typically heat dried.
In eastern Canada, kelp farming is highly regulated. Harvesting areas are parceled out for lease and permits are required for harvest. Because kelp can be cultivated, the supply is more predictable and adjustable to demand.
Kelp meal vs liquid kelp
Choosing which type of kelp fertilizer to use depends on what you want to use it for. Liquid fertilizers are quickly absorbed by plants, but also short-lived. They can easily wash away with overwatering or rain. Liquid fertilizers are good for giving a quick boost to your plants or in container gardens. With kelp meal, the powder needs to decompose in the soil before the nutrients become available for your plants. This means it will have an effect on the soil as well as the growth of your plants. The fertilizer will feed the microorganisms in your soil, and help your soil better hold onto water and nutrients.
What are the differences between Seafeed and kelp meal?
The two main differences between Seafeed and kelp meal are the diversity of seaweeds used and production methods. Production methods have less impact on the health of your soil and plants so we will focus on the different seaweeds used.
Because kelp meal is made of a single species, it is a much more uniform product. It provides vitamins and minerals, as well as some biostimulants like fucoidan and laminarin. 2
On the other hand, Seafeed contains a blend of red and brown seaweeds that is more concentrated in micronutrients than kelp alone. Red seaweeds provide biostimulants not found in brown seaweeds, like carrageenan and furcellaran. 3 By using both red and brown seaweeds, we combine the best of both worlds with a wider variety of biostimulants.
Finally, the different species of seaweeds we use decompose at different rates depending on the texture of the seaweed. For example, irish moss has thinner fronds that decompose quickly, while Furcellaria is thick and rubbery, requiring more time to decompose. Thus, nutrients are slowly released into the soil, feeding your plants for months instead of weeks. (Yay, less maintenance!)
What does the research say?
Because kelp is cultivated commercially, there is significantly more research on it’s potential as a plant biostimulant. On the other hand, the majority of red seaweeds studied are species found in the tropics where different species are farmed and warmer temperatures allow for faster growth.
Many, many, many studies prove the effect of kelp on different types of crops, ranging from corn to soybean. Kelp extracts increase crop yield as well as the quality of the produce. It made plants more tolerant to stress from heat, drought, salinity, and pests and diseases. 5
For red seaweeds, research papers are fewer and further between. But what is available shows similar effects of red seaweeds on plants. They also provide better crop yield and quality, better resistance to stress, better root growth. 3 ; 6
Fun fact: One of the biostimulants in red seaweed is carageenan, a gelling compound. It is commonly used as a thickener in food, drinks, and even toothpaste!
How to use seaweed fertilizers
Seaweed products can be used on all plants, including indoor plants. We prefer using granulated seaweed that acts on both plants and soil. It is also less likely to be washed away before plants have the opportunity to use the nutrients. Liquid seaweed fertilizer can be used when your plants need an immediate, short-term boost of nutrients, or for hydroponics.
For indoor plants
For houseplants, the easiest method is to incorporate dry seaweed when repotting. Simply add it to your soil mix. You can also topdress plants at any time. To prevent mould or a crust, incorporate it into the first half inch of soil.
You can also use liquids which will need to be used on a regular basis, generally once or twice per month.
For the vegetable garden
This is my favourite way to use seaweed! It not only helps the plants thrive, but it also increases the nutrients your vegetables. This makes them healthier and tastier!
Most seaweed fertilizers (including Seafeed) can be used at any stage of growth. They are particularly beneficial for seedlings, to give them a stronger start. Seedlings become more resilient and are better able to adapt when transplanted. They are also less likely to be affected by pests or diseases.
Each seaweed product is different, so always refer to the directions on the label for application rates and timing. For Seafeed, we recommend applying it twice per year. If you start your own seeds, add some to your soil mix then add a little more when transplanting. This should be enough enough to keep your plants happy for the entire growing season.
In the garden
Seaweed can be applied anywhere in your garden. It is particularly beneficial when planting new plants to help establish roots, and for giving a boost of micronutrients to plants that aren’t thriving. Annual flowers really love the micronutrients in seaweed. They produce more blooms that seem to just keep coming throughout the growing season.
Conclusion
There is no doubt that seaweed has incredible benefits for plants. They act directly on the plant’s metabolism to make it more resilient and productive.
While they don’t replace compost, manures, and other amendments, they can be a great addition to a holistic approach to soil health. When you invest in the health of your soil, you are feeding your plants sustainably. To learn more about soil health and easy ways to improve it, head over here.
Just remember that with biostimulants, a little goes a long way. Happy gardening!
References
Mouritsen, O. 2013. The Science of Seaweeds. American Scientist. [accessed April 17]; 10(6):458.
https://www.americanscientist.org/article/the-science-of-seaweedsShukla, P. S. , Mantin, E. G. , Adil, M. , Bajpai, S. , Critchley, A. T. , Prithiviraj, B. 2019. Ascophyllum nodosum-Based Biostimulants: Sustainable Applications in Agriculture for the Stimulation of Plant Growth, Stress Tolerance, and Disease Management. Frontiers in Plant Science. [accessed April 17]; 10: 655. https://www.frontiersin.org/journals/plantscience/articles/10.3389/fpls.2019.00655/full#h15
Shukla, P. S., Borza, T., Critchley, A. T., Prithiviraj, B. 2016. Carrageenans from Red Seaweeds As Promoters of Growth and Elicitors of Defense Response in Plants. Frontiers in Marine Science. 3.
https://www.frontiersin.org/articles/10.3389/fmars.2016.00081/fullTorres, M. D., Flórez-Fernandes, N., Domínguez, H. 2019. Integral Utilization of Red Seaweed for Bioactive Production. Marine Drugs. 17(6): 314.
https://www.mdpi.com/1660-3397/17/6/314Khan, W., Menon, U., Subramanian, S., Jithesh, M., Rayorath, P., Hodges, D., Critchley, A., Craigie, J., Norrie, J., Prithiviraj, B. (2009). Seaweed Extracts as Biostimulants of Plant Growth and Development. Journal of Plant Growth Regulation. 28: 386-399. www.researchgate.net/publication/225338767_Seaweed_Extracts_as_Biostimulants_of_Plant_Growth_and_Development (Sorry, I have no idea why this url won’t link. Copy, paste into your browser to see the full text.)
Domingo, G., Marsoni, M., Álvarez-Viñas, M., Torres, M. D., Domínguez, H., Vannini, C. 2013. The Role of Protein-Rich Extracts from Chondrus crispus as Biostimulant and in Enhancing Tolerance to Drought Stress in Tomato Plants. Plants. 12(4):845.
https://www.mdpi.com/2223-7747/12/4/845
