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Why is seaweed so good for plants?

While being used in farming and horticulture for years, seaweed has traditionally stayed outside when it comes to plants. Whereas Celtic farmers used to turn kilos of the stuff through their fields its not so simple for your potted begonia. The smell alone is enough to make you think twice, and then there is the task of blending it into your potting mix. 

Luckily, agricultural applications of seaweed has been refined somewhat since the days of old (although, no shade - if you have the space to throw some fresh seaweed around your garden bed then go for it), making it far more applicable both indoors and out. 

It's nuts to think that these literal sea garden crops are so beneficial to our soils and plants. It doesn't stop there either - seaweed has a number of health benefits for us, and animals. In fact recently a Tasmanian kelp has been shown to reduce methane emissions from cows by up to 80% when added to their feed. Then there is the numerous health benefits associated with adding kelp to our own diets - from increasing iodine, adding vitamins and minerals, raising energy levels and boosting brain function. But today we're going to stick to what it does for plants, soils and our gardens. 

Point is, the stuff is gold. As seaweed decomposes in the soil, microbial activity is encouraged which in turn helps convert previously unavailable nutrients into forms that plants can take up. Its full of micronutrients in mostly chelated (so immediately available) form, increases chlorophyll  production and acts as a growth stimulant. When used as a fertiliser, it has been shown to increase crop yields and boost resistance to disease and frost. 

Research has also shown that seeds soaked in seaweed extract germinate faster, have larger roots, stronger growth and higher survival rates than seeds with no seaweed extract. When fertilised with seaweed extract, many plants see increased flowering, sweeter fruit or increased crop yields in potatoes, sweet corn, capsicum, tomato, apples and strawberries. 

The Break Down

There are a number of key hormones and acids in seaweed that are worth singling out. 

Cytokinins: Cytokinins are hormones that activate growth processes in plants meaning they stimulate cell division and therefore plant growth. 

Auxins: Auxins have a number of different functions but one of the main roles is balancing growth speed, stimulating root growth as well as ensuring buds form and open at optimal times. 

Algin: This is a seaweed extract that you might have seen in shops sold as agar agar. It can be mixed with water then added to soil to act as a wetting agent. The Algin in seaweed fertilisers therefore helps with moisture retention. 

Betaines: These guys are all about increasing water uptake and reducing plant stress. 

Seaweed Types

In fertiliser, the most common form of seaweed used is kelp. While seaweed describes a number of different marine plants and algae, Kelp is the largest subgroup of seaweed. Not all kelps are created equal mind you, which is why for our latest product - The Plant Runner Bio Pellets - we've selected three specific types of kelp known for their growth promoting properties. 

Laminaria - can help plants recover from viruses

Sargassum - rich in Algin.

Ascophyllum nodosum - high levels of cytokinins and has the highest mineral content of any kelp

How To Use Seaweed in Your Garden and On Your Plants

Its important to remember that seaweed should be harvested only from seaweed farms or by picking up seaweed washed up on shore.

When gathering seaweed, going for the stuff 'mid-beach' will be drier that the seaweed closer to the shore, making it lighter and easier to transport. 

Its also worth considering that even washed up seaweed has a role to play, so when gathering try to take from different areas on the beach to ensure you minimise your impact. 

Once gathered, you want to apply to your garden within about 36 hours otherwise it can get sludgy and slimy and harder to use. There are a few different ways you can use your haul:

  • As a mulch - when using as a mulch, apply in thick layers as it will shrink down over a few days. Using as a mulch can help prevent weeds as well as deterring slugs, snails and other pests (so great for around the veggie patch!)  
  • As a 'tea' - add your kelp into a bucket full of water and leave for a few days to brew. Its not going to smell great (so maybe keep it outdoors only) but makes a great foliar spray and soil conditioner. 
  • Turned through the garden beds - Turning through the soil will condition your garden bed and add beneficial nutrients to the garden. 

These methods are all great for outdoor beds and outdoor potted plants, but keep in mind seaweed does smell and using indoors is not advised. Luckily, when dried and pelletised like in our Bio Pellets or added to our Indoor Plant Food, there is almost no overpowering smell like you'd get from fresh seaweed straight off the beach. 



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