Seaweed fertiliser is one of the cheapest and most effective organic plant-nourishing agents the New Zealand gardener can lay his or her hands on. In this article we’ll show you why seaweed fertiliser is so good, how to use it and even how to make your own.

Time Tested Fertiliser

Seaweed fertiliser has been used for centuries. As far back as the Celts, people were gathering up the abundantly available weed they found on the shore and using it to promote healthier, quicker growing crops.

Commercial seaweed fertiliser comes in liquid, powdered and granular forms. The liquid varieties can be used both for root and foliar (through the leaf) feeding.

Quick Compost

Seaweed has a broad and well-balanced range of nutrients. And not only is it packed with plant nourishment, the nutrients are easy to get at too. Unlike land plants, seaweed isn’t built from cellulose and so breaks down rapidly in the compost heap, releasing its goodness and encouraging the breakdown of other compost material.

Seaweed Fertiliser Advantages

One of the greatest advantages of seaweed fertiliser is that it’s all-natural, you can use it in your garden confident that you aren’t spreading a cocktail of dangerous chemicals. But there are plenty of other reasons to use it too.

Complex Carbohydrates

Seaweed contains complex carbohydrates. These stimulate microscopic soil fungi and microbes. These little garden helpers increase the availability of soil nutrients and they also play a significant role in defending against soil-based diseases.

The nutrients in seaweed fertiliser promote early flowering, stronger crops, and increased sugar content in fruit.

Acid and Iron

Seaweed contains mannitol and alginic acid both of which acidify the soil and help plants absorb nutrients.

Seaweed also adds iron to the soil, so plants that like both an acid soil and iron (e.g. gardenias, camellias, azaleas etc.) will thrive with seaweed fertiliser.


The natural plant hormones in seaweed like betaines encourage chlorophyll production, the germination of seeds and the growth of roots.

Use seaweed fertiliser to counter the effects of “transplant shock” whenever you uproot and replant. Use it on cuttings, too, to help them establish themselves more quickly.

Seaweed hormones increase the thickness of plant cell-walls, thereby creating stronger plants with greater structural integrity, pest resistance and frost endurance.

Good for Us Too

Seaweed supplies selenium and iodine, both nutrients which our New Zealand soil is poor in. The addition of these elements to food crops results in plant foods with higher nutritional value.

Pest Protection

By weakening nematodes and retarding their ability to breed, seaweed protect plants against attack from this pest.

Homemade Seaweed Fertiliser

If you have a readily available supply of seaweed it is a simple matter to make your own liquid fertiliser, just follow the steps below.

Note: Before you go gathering seaweed, check with your local council. Taking seaweed maybe illegal in some areas and may also harm delicate shoreline ecosystems.

  1. Gather your seaweed.
  2. Hose it down thoroughly to remove all salt deposits.
  3. Place seaweed in a large, topless drum with an equal amount of fresh water.
  4. Allow to sit for 8 weeks, stirring every 3 days.
  5. Decant the resulting liquid.

This fertiliser is very strong and can burn plants if not diluted well. Use 1 cup of fertiliser to a bucket of water.

Gift from the Sea

If you want stronger, faster-growing plants that germinate and root more effectively, produce sweeter fruit and higher yields and are more resistant to pests and disease, you can’t go far wrong with seaweed fertiliser.

To learn more about making your own seaweed fertiliser check out this video.

How to Make and Use Seaweed Fertiliser, 4.6 out of 5 based on 8 ratings

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  1. Mike King says:

    Brilliant and easy, thanks. I enjoyed the video.

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    Rating: 5.0/5 (1 vote cast)

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