An eminent bio accumulator

[Journal 3] Design Element – There are over 14,000 types of seaweed though in horticultural terms we need only talk of their relative merits by broad groupings of colour.  Seaweed of all colours accumulates many useful things, and some not so useful things, for our soils.  As an organic source of minerals you can’t really beat seaweed and for many of us it’s free and only as far away as the closest beach.

A rich bounty of minerals and nutrients

At least once a week the dogs and I head down to the local beach for a walk.  In the back of the utility wagon I always carry a three-pronged rake and a weed bag.  Tools that make collecting seaweed a lot easier.  On this particular beach, assuming we’ve had some recent stormy weather, there’s always a reasonable chance we’ll find a good mixture of green, brown, red and white seaweed.

Most of you will have heard that seaweed is good for your gardens and orchards.  But what does it provide and how does it help? Well it’s a long list!

At the top of the list would have to be the shear variety of minerals and trace elements seaweed contains. While seaweed contains some amounts of phosphorous, calcium and magnesium I value it more in the orchard for the trace elements it supplies.  Seaweed contains upwards of sixty different trace elements that are uncommon in other mineral sources that we might typically use in the orchard.

Thanks to the actions of a number of natural chelating compounds, organic molecules that chemically bond themselves to minerals, present in seaweed the trace elements come in a form that can be immediately taken up by our crops. These chelating compounds not only unlock the trace elements they also hold them nicely in the soil, ready for our crops, so they are less likely to leach away.  As an added bonus they continue work on trace elements already locked away in the soil. The net result is a gain of trace elements in excess of the amount supplied by the seaweed.

While small in quantity certain trace elements play a critical role in the development of plants and our trees.  To put this into context lets look at just a few of the more notable trace elements and their role in plant development:


One of the most important trace elements for plants plays a critical role in energy collection for plants. Iron molecules support photosynthesis; the process plants employ to convert carbon dioxide into organic compounds using energy from the sun.  Iron manifests in the chlorophyll of chloroplasts, the photosynthesis factories that convert infrared radiation from the sun into chemical energy.


Of near equal importance to the development of plants is copper.  Copper in a phosphate form promotes elasticity of the cuticle or bark of a developing plant.  A lack of copper inhibits growth and in trees often results in the occurrence of cuticle splitting at a rate greater than can be healed.  These wounds can open the way for bacterial and viral infections.


Vitally important in the development of all seed germ, Manganese acts a loadstone that controls the magnetism in the seed germ to begin the formation of the plant.   A manganese deficiency will result in deformations of the seed germ and poor pollination. Without manganese seed germination stops, for this reason it is often referred to as “the element of life”.

So you can see how important trace elements are to our developing trees and to plants in general.  Seaweed also synthesizes vitamins.  The browns and reds have been used for thousands of years in medicine and as a source for dietary supplements, containing good levels of beta-carotene, B1, B2, *B12, C, D and E. *As I understand it certain bacteria associated to the seaweed we collect contribute the majority of the B12 present with seaweed.

Seaweed, like all living things, contains carbohydrates and lipids that break down to simple sugars and fatty acids respectively to feed the micro flora in our soils. This natural bioconversion process makes nutrients more available to our surrounding crops.

Proteins, too, both structural and active ones like enzymes, also break down firstly to polypeptides and then to amino acids. A small proportion of these molecules may be taken up directly by some crops but these also feed our microflora, which in turn can break these down to elemental nutrients like NPK, etc.

Nucleic acids constitute the genetic material in the cells of seaweed. They’re essentially a specialised polysaccharide, a long chain sugar (carbohydrate), with a phosphate backbone and are therefore rich in phosphorus.  The phosphorous is made available to the surrounding micro flora and in turn to our crops as the micro flora biodegrade.

The substances secreted by soil bacteria in the presence of seaweed include organic chemicals known as polyuronides.  Chemically similar to alginates these polyuronides also serve to condition and stabilise the soil.  

Seaweed supports our crops directly, through minerals, nutrients and hormones and indirectly by supporting the soil building process and the micro flora that live in our soils, which in turn feed our crops.

Application notes

The merits of seaweed in horticulture have been known for a very long time … A practice known as `lazy beds’ has been practiced for centuries around Ireland and Scotland on coastal areas where little or no topsoil exists.  Left to rot in beds seaweed combined with sand or sandy soil and in some cases fish waste has served as a topsoil replacement in which to grow potatoes, turnips, swedes and oats.

When it comes to harvesting seaweed you should check with your local authorities in the first instance to ensure you can indeed collect it legally and which beaches you are allowed to collect it from. 

Also as permaculture practitioners we need to be mindful of the fact that everything plays a role in its’ own ecosystem and by removing seaweed from the beach we can disrupt that ecosystem.  Beach cast seaweed no doubt provides a habitat and a food source for a myriad of life forms.Ecologically, it makes sense to pick up seaweed on bathing beaches, as authorities are more likely to remove it anyway.  I also recommend harvesting only after a storm, when there is plenty to go around, take only what you need and make sure you leave plenty still on the beach to fulfill it’s natural role.

When you’re collecting seaweed for your garden I would go for the brown varieties first and then the rest in no particular order

The brown types have far more alginates in them than the others.   In brown seaweeds alginates contribute somewhere in the order of 10-30% of dry matter.

By far the easiest way to apply seaweed to an orchard or garden is to incorporate it raw and fresh either in the mulch layer, if you have one, or on top of the sward.  By applying raw seaweed you can be sure nothing is lost from the seaweed as it might be if it were processed in some other way. 

Though if you don’t live near the sea you can purchase a dry seaweed meal and apply it as you would fresh seaweed.  Or you could make a tea out of a commercial seaweed extract.

In Seaweed in Agriculture and Horticulture W.A Stephens [24], a pioneer in the field of seaweed extracts, shares the results of many field trials using seaweed extract.

In one case in 1965 John Cooke of Funtington in Sussex produced 565 pounds of potatoes from six sets.  At the time it was believed to be a world record crop.  He achieved these results using a mixture of bone meal, wood ash, straw and compound fertliser as well as cow, pig and poultry manure together with seaweed.  The seed potatoes were soaked in a 25 percent solution of seaweed extract for two hours once a fortnight over a six-month period prior to planting.  Once planted the potato haulms were foliar fed seaweed extract every two weeks.

Trials on vegetable seedlings showed that when soaked in seaweed extract for 24 hours vegetable seedlings showed much improved root development and suffered little shock when transplanted.  Numerous field trials with seaweed extract used as a foliar spray in orchards demonstrated improved fruit production and up to four times the shelf life of fruit once picked when compared to trees not sprayed.

Now some of the commercial processes used for creating seaweed extracts are not easily replicated at home but if you have time and dedication you can make your own.

Application notes from the orchard

In the past, at the orchard, we’ve employed a recipe for making a seaweed extract described in Grasp the Nettle [25] by Peter Proctor.  To make a batch of seaweed extract simply half fill a 40-gallon drum with fresh seaweed then add a quantity of warm water (30 degrees Celsius) to make an initial solution and then top it off with cold water.  If you can use rainwater so much the better as fresh rainwater contains less chlorine and chlorine will do its best to inhibit the fermentation process. Leave the drum in a warm place, to assist the fermentation process, and give it a stir once or twice a week to aerate it.  In two months you should end up with a sweet smelling clear brown mixture.  When that occurs strain it and you’re left with the concentrated liquid.

As we have in the past implement biodynamic principles and practices at the orchard we’ve also incorporated biodynamic preparations (502-507) to our tea at the beginning of the fermentation process.  We’ll discuss biodynamics and biodynamic techniques in journal entry six.

The resulting concentrate was applied at a rate of 10% to a water solution; once again using rain water if possible, as a foliar spray three times a year at the orchard.  Before using your own brew wholesale on your orchard trees you might want to test it out on a small sample area first. 

Foliar sprays

Foliar spraying is a method of applying a specific solution as a spray onto the leaves of plants and trees.  This is a pretty expansive, complex topic and one I’m not going to attempt to cover in any great detail in this journal entry. However to understand why we use seaweed as a foliar spray let’s look at the basics behind this practice.

Field trials with seaweed have shown that plants treated, through foliar sprays; with seaweed products have shown improved leaf vigor and better resistance to pests.

It appears from my own reading on the subject that more research is required to fully understand why plants benefit from this specific treatment but many agree that this is due in part to the minerals and trace elements we get from seaweed.  Some also believe that naturally occurring antimicrobial substances found in seaweed also contribute to foliar health.  

The healthier the leaf the thicker it becomes.  And the thicker it becomes, generally speaking, the more sugars it can generate from photosynthesis so the healthier our trees become.  The healthier the tree is the more resistant it is to disease and pests.

Foliar spraying can be a highly efficient and targeted treatment but there are many factors governing its success and that is why many report greatly varied results from the application of foliar sprays. To better explain this we need to dig into some basic botany.

Our orchard seedlings gain nutrients from both the soil, through their roots, and from the air, through their leaves.  Both are leveraged to get the right levels and balances of energy, nutrients and minerals in place for optimal health.  Leaves are responsible for photosynthesis. They achieve this through chlorophyll filled cells, in a region of the leaf known as the mesophyll layer.  The skin of the leaf known as the epidermis, and the cuticle, a thin waxy layer covering the epidermis, work together to protect the mesophyll layer from sap sucking insects and from dehydration. Stomata, slit like openings in the leaf surface 9 as can be seen in the image below), also work to regulate hydration, air and plant food energy both in and out of the leaf.  Each stomata slit is opened and closed by two modified epidermal cells. These stomata provide us a back door, so to speak, to get the contents of our foliar sprays past the defense systems and into the leaves themselves.

By Leaf_epidermis.jpg: Louisa Howard (Dartmouth electron microscope facility) derivative work: Laitr Keiows (Leaf_epidermis.jpg) [Public domain], via Wikimedia Commons

In our fruit trees, as they are deciduous, the majority of stomata can be found on the underside of the leaf.  They are extremely sensitive and for foliar feeding to be truly effective we want these stomata to be open as much as possible during spraying.  Stomata tend to contract in hot temperatures, to conserve water, so it’s best to apply foliar sprays is in the very early morning or evening when temperatures are a little cooler.  When spraying with a backpack sprayer we spray the solution as fine mist.  The finer the better and we also tend to spray upwards so we’re achieving good coverage of the underside of the leaf surface.

You can also use the seaweed tea, with a spreading agent such as soap or detergent, as part of a natural insecticide spray.  The potassium ions from the seaweed tea are directly insecticidal.  So, for example, a good control for aphid infestations would be seaweed and detergent in a dilute spray.  The potassium also kicks in to bolster the plant’s general resistance to pest organisms once the initial infestation is suppressed.

Seawater is in itself full of minerals and trace elements.  A seawater foliar spray made from one part seawater to twenty parts fresh water is a great addition, from time to time, to your irrigation plan.

My personal experience with foliar spray solutions is limited to seaweed and indeed some biodynamic applications that I’ll cover in journal entry six.  Aside of foliar spraying, whenever it’s possible, we also incorporate fresh seaweed around the drip line of our trees at the orchard.

We also apply good quality compost in and around our trees at least twice a year.  One of the many components of that compost is seaweed. Aside of the various minerals and nutrients that seaweed provides it also acts as a compost activator so helps to get the compost pile cooking when it’s made.

So what is good quality compost?

So while we’ve touched on the topic, lets take a quick look at what makes for good quality compost.

Compost is a complex residue of partly oxidized vegetable and animal matter together with substances synthesized by fungi and bacteria which break down these wastes

Sir Albert Howard

At a high level compost creation involves microorganisms breaking down raw materials and then synthesizing them into what is known as humus.

In GROW BIOINTENSIVE COMPOSTING and GROWING COMPOST MATERIAL by Ecology Action Staff [27], humus is described as “A partially decomposed, transformed, synthesized and more `stable’ form of organic matter than the original plant materials.”

Humus is packed with microorganisms, primarily bacteria and fungi, and they provide us with good quantities of nitrogen, biologic carbon and other minerals present in a form that is both stable and available to the soil community.  These primary constituents of compost are vital to the health of our soil community. A good quality compost could well have a high humus content of around 30-40% organic matter.

I have a growing collection of GROW BIOINTENSIVE material and have always had John Jeavons – How to Grow More Vegetables than you ever thought possible on less land than you ever imagined [28]- on hand at all times. Ecology Action, the organisation behind the GROW BIOINTENSIVE techniques are rediscovering the principles behind old traditional farming methods through solid science and thorough research.

John Jeavons attests that with GRO BIOINTENSIVE it’s possible to grow an amount of soil in 8 and a half years that it normally takes 500 years to grow’

Now compost and seaweed are literally worlds apart but you can see how they work together to support soil health and that of our orchard trees.  In permaculture the design process is very much about finding common connections between design elements and working with them as part and parcel of the whole design implementation.  We’ll leave compost there for the moment.  In Journal entry six, on Biodynamics, we’re take a closer look, but for now let’s direct ourselves back onto the subject of seaweed.

A natural approach

At the orchard we use seaweed in a number of ways to assist the soil building process.  We’re also using seaweed to feed the communities that live in the soil and nurture our trees. 

The fantastic range of trace elements and nutrients seaweed provides will also be taken up by our trees improving their health and the potential of the fruit we grow.

The work we do with seaweed at the orchard is part and parcel of an overall permaculture design that includes other design elements, techniques and practices working together as system.

The downside

Aside of the good things seaweed provides us it also known to bio accumulate toxins and heavy metals if they’re present in the water.  And if you introduce such things into your garden there’s a reasonable chance they’ll make it into your crops.  So it’s not a good idea to collect seaweed near industrial zones.  Find a source that comes from relatively clean water and you should avoid these problems. 

[24] Seaweed in Agriculture and Horticulture by W. A. Stephenson Published by Bargyla and Gylver Rateaver as a reprint in the Conservation Gardening and Farming Series C: Reprints ISBN 0-9600698-3-6

[25] Grasp the Nettle. Making Biodynamic Farming and Gardening Work by Peter Proctor with Gillian Cole.  A Random House New Zealand publication ISBN 1-86941-657-0

[26] Sir Albert Howard – An Agricultural Testament at this Wiki

[27] GROW BIOINTENSIVE COMPOSTING and GROWING COMPOST MATERIAL by Ecology Action Staff.  Self-teaching mini-series booklet #32.  A GROW BIOINTENSIVE TM publication

[28] How to Grow More Vegetables than you ever thought possible on less land than you ever imagined by John Jeavons. A Grow Bio Intensive Publication ISBN: 1-58008-233-5 –

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