What is Seaweed Fertilizer?

Mary McMahon

Seaweed fertilizer is fertilizer which is derived from seaweed. Seaweed is rich in vitamins and minerals which can be beneficial to plants and it is a very balanced fertilizer product which can be safely applied to many different kinds of plants. Special formulations which have been developed for particular types of plants are also available.

Seaweed is rich in vitamins, minerals and other nutrients.
Seaweed is rich in vitamins, minerals and other nutrients.

People have been using seaweed as a crop fertilizer for a very long time. Historically, seaweed was spread directly onto the fields. The seaweed acted as a mulch, which was especially useful in areas where the soil was thin and of poor quality, as the seaweed prevented soil loss, and it also provided nutritional support to the plants. However, seaweed breaks down slowly, and modern seaweed fertilizer is usually made with processed seaweed, a departure from the days of applying seaweed directly to the garden.

Dried seaweed.
Dried seaweed.

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Seaweed fertilizer is available in liquid and meal forms which can be spread on the garden. Foliar feeding sprays based on seaweed are also available. In addition, it can be included in combination fertilizer products and it is also sold in the form of concentrate. The precise balance of nutrients in seaweed fertilizer varies, depending on how it is processed and what is blended in with it, and the container should provide specific information about the contents.

One advantage to seaweed fertilizer is that it is often available in a completely natural form, a concern for some gardeners. It can also be found in certified organic fertilizer blends, for gardeners who are maintaining organic gardens. With the exception of concentrated seaweed fertilizer products, seaweed fertilizer is also unlikely to cause fertilizer burn, and gardeners do not have to worry about accidentally applying a little bit too much to their crops. This product also acts as a soil conditioner, enriching the soil and helping it retain its structure.

Most garden stores carry this product and can order it by special request if customers have specific needs. It is also possible to order it directly from companies which harvest seaweed and make seaweed fertilizer. Shipping fees can be costly when ordering this product, and people may want to ask about volume discounts or consider making a big order with a friend to make the shipping costs worth it. For special needs plants, it is advisable to purchase fertilizers specifically formulated for those plants, and gardeners should also remember to use tools like soil testing to find out how much fertilizer their soil needs.

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Discussion Comments


My sister makes her own seaweed organic fertilizer by leaving fresh seaweed in a bottle of water to decompose. She mixes this solution with more water and waters her plants with it.

@SarahGen -- I've used both liquid seaweed fertilizer and seaweed meal and I think they both work well. The frequency at which it should be applied depends on your plants and how they respond to it. If your corn looks greener and is growing well, you can keep applying it once a week or once every two weeks.

As much as I like seaweed fertilizer, I have to say that it's not the most nutritious fertilizer out there. I don't rely only on seaweed. I also use soybean meal fertilizer and calcium fertilizer in addition to the seaweed. I think you should do the same.


This is great information. I've been using synthetic fertilizers with ammonia and nitrates and they've burned my corn. I have to switch to something natural, that has safer amounts of nitrogen. Organic seaweed fertilizer sounds like a great option.

What are the prices like for seaweed fertilizer? Has anyone here been using it? Do you have any tips for me about application? Should I get the liquid kind or as a meal? How often should I apply it?

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