Homegrown Handmade
Very few things in life are free, but a wonderful garden resource is lying around, going to waste, and it will only cost you a trip to the beach.
6 ways to use seaweed to improve your plants & soil
Seaweed has many uses. It was once considered a medicine. Lady Mary Ann Martin wrote in Our Māoris (1884): “For swelled joints, we applied poultices of seaweed.”
But seaweed is also a good food. Traditionally, Māori steamed or roasted it, used it in soups, or ate it raw. It's also used as fodder for livestock and to make fertiliser.
Seaweed ‘manure' has been applied to soils to improve quality and promote plant growth for thousands of years. The Scots came up with a clever system of parallel ridges and trenches to grow potatoes that they call ‘lazy bed cultivation.' They dig trenches, layer seaweed on the ridges, and leave it to rot for several weeks.
It's then covered with loose soil from the trenches, and potatoes are planted on top. The seaweed is the only fertiliser required for a bounteous crop of spuds.
The 'lazy' beds warm up more quickly than flat ground. Cold night air filters down into the trenches, protecting the plants from frosts.
The following year they dig trenches in a new spot, and the old ones are turned over to create beds full of nutritious, productive soil.
In France, coralline (red) seaweed was used to ‘sweeten' the soil. Contemporary studies have shown that red seaweeds contain up to 80 percent lime (calcium carbonate), which can raise soil pH.
How does seaweed help soil
Studies show that seaweeds contain substances that help improve soil structure. Jelly-like alginates in brown seaweeds bind soil particles together.
They contain natural growth-promoting phytohormones, important plant nutrients such as nitrogen, phosphorus, potassium, and more than 60 minor nutrients and trace elements. Various amino acids improve microflora growth, which in turn enhances soil.
Studies of seaweed extract used at the germination stage (compared to a control group) show plants have:
• increased root and shoot growth;
• healthier foliage, flowers, and fruits;
• greater resistance to pests and diseases.
Seaweed has been used in gardens, as a medicine, and as a food for centuries.
Collect seaweed from the beach, but only where it has naturally washed up onto the shore
■ Don't harvest plants that are still growing as it's an important habitat for sealife
■ The best time to forage is after a storm
■ Use something like a garden fadge to transport it home, so you keep your car clean
1 Disease prevention
In one Australian study, crops treated with seaweed extracts showed resistance to specific diseases, including:
■ Albugo candida, the cause of white blister rust on brassicas;
■ Sclerotinia minor, a fungus which attacks lettuce;
■ Plasmodiophora brassicae, which causes clubroot.
The seaweed extracts used Durvillaea potatorum, a brown seaweed found only in the Southern hemisphere, and Ascophyllum nodosum, a brown seaweed found in the North Atlantic basin.
The Durvillaea species found in New Zealand are:
■ D. antarctica, nationwide;
■ D. chathamensis, Chatham Islands;
■ D. poha, southern South Island; Stewart, Snares, and Auckland Islands;
■ D. willana, south-eastern corner of the North Island – but not Cook Strait – South Island, Stewart Island.
They are likely to have similar properties
2 to D. potatorum. Pest control
Slugs and snails don't seem to like seaweed.
I use seaweed as mulch in my garden, and I don't have many slugs and snails. However, I'm also vigilant about clearing away weeds and debris, which provide good hideouts for them during the day, another good way to keep numbers down.
Seaweed advocate, Dr Leonard Perry of the University of Vermont, believes the salt content repels them. It's also possible it's due to the scent of iodine. Other experts say as the seaweed dries, it becomes hard, crinkly, and irritating to slugs and snails' soft undersides.
Most birds don't like seaweed either. When it's wet, they get tangled easily; 3 when it's dry, it's a scratchy deterrent. A rich fertiliser
Seaweed is an excellent source of soil nutrients. It contains nitrogen, phosphorus, magnesium, potassium, iodine, calcium, amino acids, macro and micro-nutrients, vitamins, auxins, cytokinin, and abscisic acid (ABA), and other trace minerals and nutrients.
It has been found to contribute to better growth and crop yield in plants. In soil, scientists have documented improved water-holding capacity and an increase in beneficial microbes.
You can add clumps of seaweed to the base of holes before transplanting seedlings for extra nutrition. Potatoes, tomatoes, rhubarb, and asparagus especially seem to benefit from this method, and gardeners report growing significantly larger vegetables when seaweed is used this way.