Kelp vs Seaweed- What’s The Difference

Kelp vs Seaweed- What’s The Difference?

What is the difference between kelp vs seaweed? And why are they used as fertilizer? Isn’t kelp a seaweed? What form should I pick (seaweed powder or liquid extract)? I ask myself all those questions when I look at the different organic and/or natural fertilizers available in the gardening market. 

I’ll try to answer all those questions in the next lines in the hopes you may choose better about kelp and seaweed with information on your side. 

Seaweed vs Kelp- Is There Any Difference?

Seaweed is a word used to name many species of aquatic plants, specifically oceanic ones (hence the sea- prefix). Seaweeds can grow like underwater forests, kelp beds (a type of brown seaweed) cover up to 25% of the world’s coastlines. Seaweeds create ecosystems that can host thousands of other sea creatures such as plankton, seals, fish, jellyfish, and more. Phytoplankton is also considered a seaweed because of it’s immense growth potential. 

Seaweed vs Kelp- Is There Any Difference

Seaweed is a term that includes many types of algae, including Kelp. Seaweeds grow in many marine environments (oceans, rivers, or lakes), but especially Kelp grows in shallow and cool saltwater along rocky coastlines.

Some of these seaweeds are even called sea-vegetables because they’re edible to humans. For example, nori algae (used by the Japanese in sushi and other traditional dishes), dulse, kombu, and wakame. Some seaweeds are medicinal, used mostly to treat skin problems. For more info on seaweeds and kelp, click here to open the National Ocean Service.



Include many types of algae of red, brown, and green. Brown type of seaweed
Grow in many marine environments Only grows in saltwater, along rocky coastlines in depts of 6 to 90 ft. deep
Many different sizes, some of them are microscopic Large size
Used as a liquid fertilizer from natural seaweed sources Used as a natural fertilizer and source of trace minerals and usually mixed with fish meal
  Can be found in powder or liquid kelp

GS Plant Foods Organic Liquid Kelp Fertilizer

Kelp as a Garden Fertilizer

But how does kelp or seaweed help my garden soil and veggies? In the beaches, these plants prevent sand erosion and maintain the ecosystem healthy by feeding animals, as well as providing shelter. 

In the garden, kelp and seaweeds turned out to be a great fertilizer for any kind of plant/soil nutrition deficiencies. Seaweeds are not particularly high in nitrogen or phosphorous, but they contain up to 60 different minerals which are micronutrients (trace elements) for plant health promotion. It also has pest deterring properties. Pets don’t like the smell of it, which results in keeping them away from the garden. 

Seaweeds, including kelp, certainly amend nutrient-depleted soils and improves structure, water retention rates and ultimately end up decomposing, and in the process, they add organic matter to your garden beds, pots, and composts or other fermented fertilizers.

Learn more How To Use Kelp Meal Fertilizer

Neptune’s Harvest Organic Hydrolized Fish and Seaweed Fertilizer

Foraging Seaweed for Fertilizer

If you forage kelp or other seaweeds for fertilizers, follow these tips for better results.

  • Collect only from the coastlines below the high tide mark, in small quantities, only what you need.
  • Know that there’s no need to wash the salt away, it contains minerals and nutrients.
  • Cut the plants by hand or grass scissors, sometimes they hide small stones, sand, or even shells.
  • Use fresh or dry, both ways are equally nutritious to the soil.
  • Apply over your garden beds, under the mulch, and in your compost.
  • If you buy it, it comes available in powder and liquid extracts, and different concentrations. Choose the best suitable for your project. Liquid extract for hydroponic systems seems like a great idea. Seaweed powder is more suitable for grow beds, pots, and as a compost improver.


For more useful tips and info regarding seaweeds as fertilizers, I recommend the article Seaweed Fertilizer — Using and Composting Seaweed for Your Garden.


If you use Kelp or any seaweed as fertilizer, there are a few things to consider:

  • You may forage it in small quantities, always trimming the submerged parts of the seaweed, avoid collecting it from the beach. 
  • Notice that seaweed foraging may be an illegal practice in your region. 

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