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How to Fertilize Plants with Seaweed Extract

By Contributor ; Updated September 21, 2017

Seaweed extract can be made into a rich, nutritious fertilizer for houseplants, vegetables and potted plants of all kinds. It contains trace minerals and chelating agents that plants need. Seaweed also contains growth hormones that are helpful for plant germination, and increase flower and fruit yield. Kelp is the most common form of seaweed used as plant fertilizer. The liquid fertilizer made from seaweed can be applied in the form of a foliar spray, which plants absorb through their leaves. The powdered form of the fertilizer can be tilled into the soil. You can find the extract at well-stocked home and garden stores, or online.

Add 1 to 2 tbsp. liquid seaweed extract to 1 gallon of water. Mix the two together in a plastic gallon-sized container such as a clean milk jug, and then shake to combine. This will create a foliar spray that you can apply directly to the leaves of your plants. Store the mixture in a cool, dry place until ready to use. It should make several batches.

Fill a spray bottle with the seaweed extract mixture and set the sprayer to the first setting. The finer mist is easier for plants to absorb than larger droplets.

Spray the seaweed fertilizer on the leaves of your indoor plants and on the foliage of your outdoor vegetables, including the undersides of the leaves. Apply early in the morning, while the leaf pores are still open. Do not rinse, but allow the plant to soak up the nutrient rich liquid.

For large gardens, mix 1/4 to 1 1/4 tsp. seaweed extract into 1 gallon water and inject the solution into the irrigation system. This solution is sufficient for 100 feet of gardening bed. Alternatively, you can till into the soil in 1 lb. kelp meal for every 100 square feet of garden.


Things You Will Need

  • Liquid seaweed extract
  • Empty milk jug
  • Spray bottle
  • Kelp meal


  • If using the foliar seaweed spray, use only once per growing season for vegetable plants. Use the liquid fertilizer once every two months for house plants and potted plants.
  • Apply seaweed extract to plants only during their active growing season.

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