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seaweed as fertilizer

Want to boost your soil? Get some seaweed

If you can afford only one type of fertiliser, Alys Fowler says, make it seaweed

‘In general, seaweeds contain 10 times the mineral levels of land-based plants.’ Photograph: Alamy

‘In general, seaweeds contain 10 times the mineral levels of land-based plants.’ Photograph: Alamy

Last modified on Fri 1 Dec 2017 15.42 GMT

I am always in awe of the fact that there is a garden under the sea; that plants can not only survive but thrive in a watery world that is turbulent and ever changing.

Seaweed is magical stuff in the water, and it’s somehow even more so when out of it. It’s incredibly healthful to us, to our animals, to our soils and our plants. It seems anyone who gets to ingest a little seaweed does better for it.

As seaweed breaks down into the soil, it encourages microorganisms whose activities help convert unavailable nutrients into forms that plants can use. It increases chlorophyll production and contains many micronutrients important for soil and plant health, as well as acting as a growth stimulant: it is rich in cytokinins, plant growth hormones that work above and below ground, improving root growth.

I recently went to Inagh Valley Trust, a seaweed research centre in Connemara, Ireland. They’re developing all sorts of interesting seaweed products, including adding seaweed to manufactured bread to increase its shelf life, and creating a seaweed feed for honeybees, to improve hive conditions and combat disease.

I spent a morning geeking out on seaweed spores swirling around in glass jars as they went through propagation, and munching on seaweed health bars. Then I went to the coast and wondered how much beach-strewn seaweed I could cram into my suitcase home – and whether Ryanair would complain about the smell.

It’s very important to collect only seaweed that has washed up; it’s not sustainable for everyone to go around the rocks pulling it off. Winter storms, however, often wash up great mountains of the stuff. There are brown, red and green algae, and all have different nutrient levels, so collect a variety, if you can. In general, seaweeds contain 10 times the mineral levels of land-based plants and are particularly rich in iodine and calcium. You can put them directly on beds; they will be salty, so you can’t plant direct into them, but a winter of rain will wash the excess salt away.

If you can afford only one type of fertiliser, Alys Fowler says, make it seaweed

Seaweed as Fertilizer

Are There Benefits?

Using Seaweed as Fertilizer is an ancient practice. Any people who lived near the ocean would gather this free resource to use as fertilizer on gardens.

Many places near the coast are rocky, and don’t grow much in the way of plants to feed animals, or to use as cover crops or mulch. This means that to grow a garden to provide food, they would need to locate a material that is easy to gather, transport, and spread. Manure is not it.

Unless you have easy access to something light weight, that has high nitrogen in it, your garden will suffer.

Fortunately, seaweed is abundant at certain times of year (after winter storms, ready for the spring growing season).

It gets tossed high up on the beach, where it dries out. Added to that is that often, tiny crabs, fish and other small sea life get caught in it, which add even more nutrients. Mussels and barnacles could be in there too, which will smell a lot while they decompose.

Dogs in particular love this, so be warned!

If you’re going to collect seaweed for your garden, try to wait until it’s had a few rainfalls, so it’s not as salty. Nothing will grow in salt.

If this doesn’t get rinsed off naturally, you’ll have to do it. I’ve seen screens set up where you would pile on the seaweed and rinse it off with fresh water, or wait for the rain to do it. Then it’s ready for use in the garden.

So, get out there, take a bag or a wheelbarrow and a potato rake, and gather some of that free for the taking kelp or algae. There’s lots more where that came from.

How To Use Seaweed as Fertilizer

If your seaweed is in the form of kelp, those long strips of slimy green stuff, chop it first before you add it to your garden. They will constantly tangle up if you don’t.

For smaller types of seaweed, like Dulce, they can be chopped, or just laid on top of the soil. If they’re dry, they crumble, so put them into a metal garbage can and use either a string trimmer, or pound it with a large stick to pulverize it.

Dig it in, or lay it around the plants as mulch to decompose in place. This might take a while, so you can’t count on it as a nitrogen source unless you’ve done it for several years in a row.

Alternatively, you can compost it first, then add it to the garden in the fall.

Not living near the sea? There are other options, which left unchecked, become a real nuisance in fresh water. These are Eurasian Milfoil (escaped from aquariums by people who should know better) and Water Hyacinth.

Keep your eyes open for the special boats that are fitted out with harvesting equipment and see if you can ask for some of the weed for your garden.

The benefits of using Seaweed as Fertilizer…