5 Effective Ways to Use Seaweed in the Garden

by Corinne Mossati

Seaweed is abundant in nutrients and trace elements and has many uses in the edible garden. Here’s how to collect it and use it in the garden.


Seaweed, Golden Kelp – Photo © The Gourmantic Garden

My local beach is renowned for dumping massive seaweed which is often left for days to decompose and smell before it is collected. On a hot day in the middle of last summer, I went for a swim in the morning and the beach was covered end to end with seaweed. But something was different this time. The smell was so fresh as if it has just been cast on the shore.

Benefits of Seaweed in the Garden

Seaweed is abundant in nutrients and trace elements such as nitrogen, magnesium, potassium, iodine and phosphate. It helps plants in their uptake of nutrients and contains natural plant hormones in seaweed make it useful in minimising transplant shock when a plant is transplanted.

Golden kelp is the common seaweed along our shores but you’ll also find other types if you go foraging.

How to Collect Seaweed

First and foremost, check your local rules. According to this website, in NSW, collecting seaweed from beaches is permitted within habitat protection zones and general use zones. Collecting more than 20 litres per person per day requires a permit.

In New South Wales: ” it is legal to collect up to 20kg of beach-cast seaweed per day for personal use without the need for a permit. Anything above this weight requires a permit and collecting is not allowed in Intertidal Protected Areas, RAMSAR wetlands and Aquatic Reserves.” source

Seaweed is usually scattered in three areas along the beach: along the tide line, getting wet with the ebb and flow of the waves, midway and further up along the beach which tends to be dry. Leave the latter alone as chances are it has started decomposing, smelling and harbouring bugs. I prefer fresh clean, seaweed from the water line or midway which is lighter to carry. Don’t take any seaweed that’s attached to rock.

Pick up the seaweed and give it a good shake in case there are any critters in it. Place it in a bucket, plastic bag or onion sack. I find smaller sized pieces to be easier to manage in the garden than long strips. Pick a little from different areas to minimise the environmental impact.

How to Use Seaweed in the Garden

Seaweed Tea

Seaweed ‘Tea’ – Photo © The Gourmantic Garden

Now that you’ve collected the seaweed, rinse it immediately under fresh water to remove any critters. As seaweed breaks down easily, use it within 36 hours of gathering. Here’s how to use seaweed in the garden.

1. Use seaweed as mulch. Place it around the plants but away from the stems. Every time you water the plants, it will deliver nutrients to the soil.

2. Cut up the seaweed into manageable pieces and bury it in the soil. There’s no need to wash it. Cover with straw mulch and water. It will break down quickly and add nutrients to the soil. Like with any mulch, keep it away from the stems.

3. Leave the seaweed out to dry in the sun. You can also cut it into manageable pieces and dehydrate it if you have a dehydrator at home. Once it’s dry and crispy, run it through your food processor to break it up into small pieces and use as mulch.

4. Make seaweed tea as a tonic for your plants (see photo above). Put the seaweed in a plastic bucket full of water, cover it with a lid but not too tightly and leave it in the sun for a few days. Give the mixture a stir every day. Yes it will smell so put it somewhere away from the house. I left mine for 6-8 weeks but that was partly because I forgot about it in light of the COVID-19 situation. When the smell has subsided, strain it into a bottle and label it. To use it, dilute in 1:10 ratio of seaweed tea to water and use it as foliage spray or plant tonic. The remaining solids can be broken up to add as mulch or compost.

5. If you’re composting at home, add seaweed to the compost as well as in the garden beds.

As you can see, there are so many ways to use seaweed in the edible garden and you’ll be using a natural resource sustainably that would otherwise go to waste.

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