Organic Fertilizers: Seaweed

Seaweed is a fantastic soil or compost ammendment

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What is it?
Seaweed is a general term for any of the multi-celled ocean algae.

What is the primary benefit?
Seaweed is a great source of organic matter for our compost and our soil. It is full of beneficial trace minerals, plant growth hormones, and fully-chelated (that means readily absorbed) micro-nutrients. Depending on where we live, we may have access to large amounts of seaweed. Currently, we are just a hundred yards (90 meters) from the rocky Azorean beach. The recent storm deposited literal tons of seaweed on the shoreline (read this article I wrote about it).

Here I am harvesting seaweed from my local beach... with some help from my boys and dog.

How is it used?
Seaweed can be used directly as a mulch. It provides all the benefits listed above, but it also repells snails and slugs - natural salt content and dries out with tiny jagged edges that they despise. Just keep in mind that there will be a fishy odor from the seaweed as it breaks down, some are have a stronger odor than others. The salt content is usually not enough to cause too much issues with your soil, especially if you live where there is a decent amount of rainfall; most places with plentiful access to seaweed have sufficient rain. However, if you are concerned, you can rinse the seaweed out for a few minutes with clean water before application.

Seaweed can be composted. This is a great way to incorporate all the seaweed's benefits into our soils. Just treat it as any other "green" material. (read this article for more information about composting)

There are many types of seaweed, but they all work the same in the soil.

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Seaweed can also be used to make an emulsion-type fertilizer. There are many recipes for creating this, but the general principles are the same. Take a bucket and fill it halfway with seaweed. Next, fill it up with water. Let it sit anywhere from 2 days to 2 months. Keep in mind that this can get stinky! The longer it soaks, the more concentrated it becomes. If it only soaks for a few days, then the water can be sprayed directly on plants as a foliar fertilizer. If it soaks for a long time, then dilute the seaweed liquid with water, and then apply. Dilute more if the seaweed soaks longer, and always err on the side of applying too little.


Application:
Add fresh seaweed to your soil or compost directly.
Add fresh seaweed to as mulch around plants.
Do not use seweed to mulch garden paths - will become slippery if wet, and it shrinks when dry and is not too effective.


Composition:
NPK Ratio: 

• Dried/Composted Seaweed: 1.1-1.5/0.75/4.9
• Fresh Seaweed: 0.2-0.4/0/0

A Note About Collecting Seaweed:
Only use seaweed that has washed up on shore. Avoid cutting or pulling up established, growing seaweed. Sustainability matters.


A GENERAL NOTE ABOUT FERTILIZERS:
Always test your soil before adding any fertilizers. We can easily damage our plants and the soil by indiscriminately adding soil amendments.