What is seaweed?
Seaweed is the common name for all plants and algae which grow in the sea. The name is a genuine misnomer. Not only are they also found in rivers and lakes, but they are not really weeds at all. A weed is a plant in the wrong place. Marine plants are absolutely essential for sustaining all manor of life all over the planet, including us humans.
The more we find out about these fascinating marine plants, the more amazing they seem to become. They are packed full of minerals and trace elements. Plants oxygenate the water and lock in carbon dioxide. They filter the sea water and provide food and shelter to countless organisms. Not only have they become a sustainable, renewable resource in horticulture but some are also a delicious and nutritious food source.
Marine plants and algae vary in size from gigantic forests of kelp down to single-celled phytoplankton. There are a huge number of different species all over the world. Around the UK, the most common species of marine plant is knotted wrack (ascophyllum nodosum). This is the one most used in horticulture.
How was it found to be good for lawns?
Greens keepers at golf courses in Scotland farmed seaweed from the local beaches. They covered their greens with it during severe winters. This both protected the grass from the cold winds and leaked out a variety of trace nutrients into the soil as it weathered down. When the weather improved it was removed and composted and mixed with sand. This produced a brilliant topdressing material. A process which still goes on at links courses to this day.
In Cornwall, farmers have used seaweed as a soil conditioner on their plots for centuries. Collecting it from beaches and digging it into the soil. A practice which still occurs at the famous Lost gardens of Heligan.
With the advance of science, the nutritional content of seaweed has subsequently been proven in the lab. Farming and extraction are now advanced industrial operations, bringing the benefits of seaweed to gardeners all over the country.
Why is seaweed good for lawns?
Seaweed has been used for generations on fine lawns and in gardens. But why? It turns out that it is rather amazing stuff. It contains a huge number of vitamins, minerals, plant sugars and growth hormones. Over ten times the mineral levels of land-based plants. Not only are these much needed by grass, but they also feed the bacteria in the soil. This brings several benefits in a lawn. Bacteria in the soil break down organic matter, passing these nutrients onto the grass plants. Improving these bacteria populations improves your grass. These micro-organisms also help to reduce the thatch layer which builds up on a lawns surface. This is important to prevent it from becoming too thick and unmanageable.
Seaweed also directly feeds grass. The nutrients are absorbed as a foliar feed through the leaves or in the soil by the roots. It increases chlorophyll production in leaves helping the grass produce more food for itself. The concentrated feeds are rich in plant hormones called cytokinins. These are growth stimulants which boost grass growth, helping the lawn to green up.
Seaweed is not a true fertiliser. The nutrient content isn’t guaranteed or standardised. It is considered as more of a tonic, adding valuable vitamins and minerals. I use it in conjunction with regular fertiliser applications.
But there are more benefits for the soil!
Apply seaweed to new lawns as it is great for the soil. It can correct any pH irregularities as it can make the soil more alkaline. When added to a heavy clay soil, alginic acids in seaweed act as a flocculator. This means the fine particles clump together into a friable crumb structure, producing an improved growing medium. Adding it to a sandy soil improves the humus content and increases the nutrient levels. This goes to improve drought resistance.
Of course changing the soil doesn’t happen straight away, but when building a new lawn adding it in will help tremendously for the health of the lawn for the future.
How is seaweed applied to lawns?
Seaweed is applied to lawns in a number of ways:
- Granules mixed into the soil when initially building a lawn.
- Applied as granules or when incorporated in fertiliser to feed your lawn. This would be especially beneficial after aerating to get it down into the soil.
- Applied as a liquid bio stimulant to aid germination of grass seeds. Find out about the difference between liquid and granule lawn feeds here.
- Applied as a liquid foliar feed to established lawns throughout the year.
So start to see the benefits of this fantastic resource from the sea and apply it to your lawns this season.
References and further reading:
- National Ocean and Atmospheric Administration
- Royal Horticultural Society
- Food and Agriculture Organisation of the UN
- Premier Lawns NI
Elements include: Nitrogen (N), Phosphorus (P), Potassium (K), Barium, Boron, Bromine, Calcium, Chloride, Cobalt, Copper, Iodine, Iron, Magnesium, Manganese, Molybdenum, Nickel, Selenium, Sodium, Sulphur, Vanadium and Zinc