Use Seaweed To Fertilize Your Backyard Garden


Seaweed Is Not Just For Sushi!

Green SeaweedBrown Kelp







Seaweed is also known as kelp – and the words are used interchangeably in this article.  The technical difference is that most of what we call “seaweed” is green – and, when the seaweed is brown, it is typically called “kelp.”

Either way, it has been a food staple in Asia for many years.  Seaweed has been used in salads, stir fries, and, of course, it is best known as a sushi wrapper.

Seaweed wrapped sushi.

But, did you know that this ocean plant is a great addition to your compost pile – or, added directly to the garden – as a fertilizing mulch?

Kelp is jam packed with as many as 5 dozen nutrients that a healthy vegetable plant needs.

It begins breaking down almost immediately as it begins to dry out under the sun’s rays.


Where Can You Get It?

I always keep a supply of plastic grocery store bags in my vehicle for any number of reasons – and they will work well for collecting seaweed.  I prefer using burlap bags or onion bags because they drain well but the plastic bags work fine.

Seaweed on an ocean beach.

For those of you living close to the ocean, take some bags with you when walking the beach and collect seaweed that is ideally in the mid-tide area.  This seaweed is a new arrival and not too many sea and beach critters have taken up residence in it yet.

Older seaweed, farther up the beach, will work but, it may have a more pungent odor and a higher critter population.

Either way, grab a handful, shake it a bit to remove excess sand and beach bugs, and pop it in the bag.  A leisurely walk on the beach can produce 10 or 20 bags of kelp for use as a garden soil amendment.

Seaweed can also be found in fresh water lakes.  However, because of the possibility of toxins and heavy metals being absorbed due to dumping from some manufacturing facilities, I try to avoid fresh water seaweed.  You never know what you are going to get – and, if your plants absorb it, then these poisons will inevitably get pass along to you.


How To Use It?

First – stick the seaweed in a barrel and soak it in fresh water – then rinse and repeat.  This will remove any excess sea salts, sand, and critters that hitched a ride home in the bags.

Next – Spread the kelp out to dry in the sun for a few days.

Finally – Mix it into your compost pile – or add it directly to the garden, placing it around the plants on top of the soil.  Alternatively, you could make a compost tea with it – by sticking it back into water and let it soak for a couple of weeks – then drain the juice and spray it on leaves, stems, and around the base of the plants.  Seaweed has a high potassium content which is an excellent helper to your veggies during flowering and fruiting stages.

NOTE:  If you put the kelp directly into the garden, don’t work it in to the soil – just lay it on top – around the plants – as mulch.  Even though it is nutrient rich, if it is worked into the soil, it will draw nitrogen away from your veggies and we don’t want that.  But, spreading it around the plants on top of the soil allows it to be drawn into the soil naturally by worms and Mother Nature – so, it becomes a time release method of adding its special nutrients to the garden soil.

My preference is to add the kelp to my compost pile and mix it in thoroughly.  It will decompose quickly and be a ready addition to the garden in a month or two.


What If You Don’t Live Close To The Ocean?

There are several great seaweed fertilizers available that will do great things for your garden plants.

GS Plant Foods has a 1 gallon liquid concentrate, Liquid Kelp Organic Seaweed Fertilizer.  It is made from Norwegian kelp – which has been proven to be most effective at maintaining healthy plant growth – stronger root systems – bigger flowers and fruit – and many other benefits.  It also adds additional microorganisms to the soil that can fix nitrogen from the air – the same way that a soil inoculant does.

Liquid Kelp Organic Seaweed Fertilizer

Add 2 ounces of the concentrate to a gallon of water and use a garden sprayer to leaves, stems and bases of plants for best results.  I’ve got a 3 gallon Chapin Garden Sprayer that has served me well for a long time!

Chapin Garden Sprayer

Then, there is Blue Planet Nutrients Liquid Seaweed in a 1 gallon liquid concentrate.  It basically does the same thing as the GS Plant Foods product – and the application rate is only 1 ounce of concentrate to 1 gallon of water – added to a garden sprayer.

Blue Planet Nutrients Liquid Seaweed


Either one of these will enhance your veggie growth, increase fruit size, increase size of harvest yield, extend the plants’ growing life, increase flavor, increase disease protection, and help ward off pests that want to do harm to your crop.

If you keep the containers in a dark area at room temperature, the seaweed fertilizers will still remain potent for at least a couple of years.


Time For Something Faintly Funny…

Two pieces of green seaweed limp slowly into a police station and approach the desk sergeant.

Desk sergeant, “What the heck happened to the two of you?”

The first piece of seaweed says, “It was ghastly!  It was horrific!  It was just unspeakable!”

The second piece of seaweed blurts out, “We were attacked by Popeye!  He thought we were spinach!”

Popeye looking for spinach.

Have you tried using a seaweed fertilizer?  What were your results?  What do you recommend?  Leave a comment or email me,


Jim, The Lifelong Gardener

2 thoughts on “Use Seaweed To Fertilize Your Backyard Garden

  1. Ann Reply

    I had heard about seaweed fertilizers but hadn’t thought about collecting seaweed from the beach to use.
    Thanks for explaining your tip about laying the seaweed on top of the soil and not digging it into the soil.
    I like your suggestion of adding the seaweed to the compost heap. I remember my father’s compost heap which had all of our scrap veg peelings added to it. I’m glad to see the compost heap making a come back.
    Collecting seaweed from the beach seems like a great way to recycle too.

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