What is in liquid seaweed fertilizer?

Updated March 27, 2017

Seaweed, including common varieties such as kelp and eel grass, has many beneficial properties that can help your garden prosper. Indeed, these qualities cause many to consider seaweed the perfect compost and fertiliser additive.

NPK Rating

Most commercial liquid seaweed sprays have an NPK (nitrogen-phosphate-potassium) rating of 0-0-1, making liquid seaweed a gentle additive.

Growth Hormones

Seaweed contains many growth hormones; a soil soak of liquid seaweed extract will encourage root growth in young plants. You can also soak seeds for 24 hours before planting to stimulate germination.

Trace Elements

Liquid seaweed extract is a complete source of plant-based minerals, containing up to 60 trace elements; mist your plants and they will absorb these nutrients through the pores of their leaves.

Disease Control

The foliar spray technique also helps to block disease and discourage sap-sucking insects.


Alginates, spongelike starches found in seaweed, hold water droplets near the plant roots, making moisture available to them without drowning them; they also help enrich the soil by feeding myriad beneficial microorganisms such as bacteria and tiny fungi necessary to composting.


Rinse the excess salt off fresh or dried seaweed. Chop into small pieces. Fill about half a plastic dustbin with this material, top off with water, cover, and leave to decompose for 2 to 3 months. Dilute 1:1 before use.

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About the Author

Nicole LeBoeuf-Little is a freelancer from New Orleans, writing professionally since 1994. Recent short stories appear on and in Ellen Datlow's anthology "Blood and Other Cravings." She has published articles in "Pangaia Magazine" and eGuides at She holds a Bachelor of Arts in English from University of Washington and attended the professional SF/F workshop Viable Paradise.