How to Use Seaweed As Fertilizer

Updated April 17, 2017

Many gardeners use seaweed as an organic fertiliser to supplement their plants' nutritional needs. Trace elements found in seaweed include magnesium, potassium, and nitrogen, which are beneficial to plants. Because seaweed is a completely natural product, you can use it to fertilise your soil knowing that you are not adding any toxic chemicals, which may be found in commercially produced fertilisers. If you are lucky enough to live near the ocean, you can collect your own fresh seaweed; if not, dry seaweed powder and liquid seaweed fertiliser do the same job.

Collect fresh seaweed that has been washed ashore and use a bucket to take it home.

Transfer the seaweed into a colander. Rinse it under fresh running water to get rid of all salt and sand.

Chop the seaweed into 2-inch pieces using a shredder-grinder.

Apply two handfuls of the clean seaweed pieces to the dirt around your plants.

Add 1/4-lb. of organic seaweed fertiliser powder to 1 gallon of water.

Stir the mixture thoroughly with a large wooden spoon, then leave it to steep for one to three days.

Swirl your mixture gently, then strain it.

Apply the strained seaweed fertiliser to your soil.

Spray liquid seaweed fertiliser on the leaves of your plants a couple of times a month during growing season, first when your plants are first leafing and then when the buds are forming. Apply it in early morning, when evaporation is at its lowest.

Add 1 tbsp of liquid seaweed fertiliser to 1 gallon of water and apply the diluted fertiliser directly to your soil as an alternative to a spray application.

Repeat the application once a month after the growing season is over.


Use seaweed fertilisers alongside other solutions, such as worm castings or guano for the best results.

Things You'll Need

  • Colander
  • Shredder-grinder
  • Large wooden spoon
Cite this Article A tool to create a citation to reference this article Cite this Article

About the Author

C. Giles is a writer with an MA (Hons) in English literature and a post-graduate diploma in law. Her work has been published in several publications, both online and offline, including "The Herald," "The Big Issue" and "Daily Record."