Perfected over billions of years, nature always provides a solution far simpler and more effective than anything we can dream up in a whole lifetime.
 

Every day with a hiss and a foam our beaches wash up a gift for gardeners – tonnes of seaweed bursting with nutrients and what’s more it’s free. Every year the council for Altona beach spends around $300,000 to remove it, $300,000 to beautify a beach from seaweed! It is either dumped in landfill or washed(!) and returned to the sea! I discovered this when I was researching to see if it was legal to gather seaweed in Melbourne, I’m going to go ahead and assume yes on this one.

A small percentage is now being converted into liquid fertiliser, which is a start, but wait a second…why does it need to be commercially processed to turn it into a liquid or dehydrated powder and bottled in plastic and delivered to a nursery and purchased for $10/L and diluted and sprayed on your garden and the bottle thrown in the recycle bin? Why do all that when it is the most divine mulch you’ll ever use and all you have to do is spend a day at the beach?

Now that sounds like an excellent way of saving time, energy and money!

WHY I USE SEAWEED MULCH

2.5 years ago we started our first vegetable garden. My mother gave me a jar of powdered seaweed for out little 1mx1m pallet garden, part of a no-dig recipe sprayed between layers of dry straw. Then Permaculture crept in and with it shiny tomes raving about seaweed tea, how could I resist making my own brew? The result, well…it was smelly, honestly it stank like a sewer! And some mosquitoes got in and that was the end of that idea! There had to be an easier way! There was – it was simple, just rinse it and spread it on the garden beds, done, easy. When my other quizzed me on it, I didn’t really have an answer, mulching is good, seaweed is good so don’t they make a perfect pair? I retaliated with research and was pleasantly surprised that it was actually a brilliant thing for your garden!

AND WHY YOU SHOULD TOO

• nutrient rich and the nutrients are easily absorbed by plants
• trace elements are transferred to the plant and its fruit, more nutrient rich for you too
• free and easily accessible and free, a beach holiday once or twice a year is all you need
• contains very little salt, the sand is what makes it too alkaline and this can be washed off
• soil conditioner, healthier soil
• plant conditioner, healthier plants
• make plants more resistant to disease, shares no diseases with land plants
• deters pest like snails and slugs
• keeps soil moist – less watering (less heat stress)
• insulates the soil – cool in summer, warm in winter (makes plants more frost resistant)
• suppresses weeds, contains no land weed seeds

WHAT’S IN SEAWEED?

• all major and minor plant nutrients
• all necessary plant trace elements (over 60 in total)
• alginic acid
• vitamins
• auxins
• two or more gibberellins
• and antibiotics
• No wonder they say it’s good for humans to eat too!

When I read this list I’ll admit I wasn’t even sure what some of those things were, but it’s all pretty straight forward once you can get your tongue around the words!

Don’t care about the why, here’s the how to use seaweed mulch.

PLANT NUTRIENTS

These are all essential for plant growth and health, they are a plants food and drink.

NON-MINERAL NUTRIENTS

(hydrogen, oxygen, carbon) are provided by air and water, converted using the sun’s energy (photosynthesis) into starches and sugars. However, all the other required nutrients can be provided by seaweed.

MINERAL NUTRIENTS

dissolve in water and absorbed through plant roots. When soil minerals are not in balance plants become sickly. This is exacerbated when the same crop is planted year after year, depleting the soil of specific elements.

MACRO-NUTRIENTS

• primary nutrients (nitrogen, phosphorous, potassium)
• usually lacking in soil because plants use huge amounts to grow, these are the main ingredients of commercial fertilisers
• secondary nutrients (calcium, magnesium, sulfur)

MICRO-NUTRIENTS

• trace elements (boron, copper, iron, chloride, manganese, molybdenum, zinc)
• also can become deficient, especially without practicing crop rotation
• necessary, but only needed in “micro” amounts

BIOAVAILABILITY

Just as iron in vegetables (non-heme) can be harder to absorb than iron from meat (heme), the minerals you are adding to your soil need to be in a form that is usable for the plants otherwise it won’t be absorbed.

Trace elements can be made available to plants by chelating (combining the mineral atom with organic molecules so they cannot form insoluble salts the plant cannot absorb).

Seaweed contains starches, sugars and carbohydrates that possess such chelating properties, so all the lovely nutrients it contains are available to the plants which need them.

VITAMINS

Soil depletion has adversely affected the vitamin and mineral content in our fruit and vegetables. Healthier soil rich in vitamins and nutrients leads to a healthier product for us to eat. Vitamins contained within seaweed include:

• vitamin C
• beta-carotene, fucoxanthin
• B1 (thiamine), B2 (riboflavin), B12
• pantothenic acid, folic acid and folinic acid
• vitamin E (tocopherol), vitamin K
• other growth-promoting substances

AUXINS & GIBBERELLINS

Encourage the growth of more cells as well as enlarge, stimulating the growth in both plant stems and roots.

SOIL CONDITIONER

The alginic acid in seaweed , whether it be fresh, dried or liquid, improves the soils ability to retain moisture and hold together. This helps to form a good crumb structure: large particles providing drainage and air movement and small pore spaces between to hold water and plant nutrients.
This means in times of heavy rain, seaweed can improves sloping, silty, sandy soil so that seedlings and nutrients no longer get washed away. Conversely when it is very hot the soil will be slower to dry out.
 

BACTERIA & NITROGEN

A good crumb structure stimulates growth of root systems as well as the activity of soil bacteria. The good bacteria secrete beneficial polyurinides that further condition the soil as the seaweed decomposes. The seaweed should be applied 3.5 months before the plants require an increase in nitrogen. This is because bacteria require nitrogen to break down undecomposed vegetable matter into simpler units, leading to a temporary reduction in nitrogen in the soil. After this latent period the overall amount of nitrogen in the soil is dramatically increased so it is beneficial to time this with for instance the fruiting of a tomato when the plant requires a little something. However, if a pick-me-up is required the nutrients in liquid seaweed are available at once and this can be used as a foliar spray absorbed directly through the leaves.

ANTIBIOTICS

Plants mulched with seaweed develop a resistance to pets and diseases. It is believed that soil fungi and bacteria produce natural antibiotics which control pathogen population reducing the likelihood of a number of plant diseases. The concentration of organic matter/seaweed in the soil increases the production of these antibiotics.

SEAWEED RESOURCES

Seaweed in Agriculture
Soil Depletion & Nutrient Loss
Altona Seaweed Control
Earth Easy Blog

 
 
 
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Fact Sheet: Seaweed Fertiliser
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Fact Sheet: Seaweed