We’re all familiar with the term ‘superfoods’ referring to foods such as blueberries and cherries that are packed with vitamins and minerals which make them great foods for us to eat. But what about a ‘superfood’ to feed our plants? Seaweed is packed with nutrients that are beneficial to humans. It features as an ingredient in Japanese cuisine and has been an important element in beauty treatments for many years, you can even bathe in the stuff in special bath houses in Ireland. But it is in the garden that most people are familiar with seaweed.
For centuries, humans have used seaweed as a soil improver and fertiliser to feed their crops. It contains the main nutrients plants need along with a whole range of trace elements that are often lacking in other fertilisers.
Seaweed proved particularly useful to crofters on the Scottish islands where the soil wasn’t very deep and lacked nutrients. Crofters practiced what was known as the ‘lazy bed’ system, where seaweed was placed next to trenches for several weeks to rot down and then incorporated into the trenches. The seaweed would provide all the nutrients and organic matter that the crops would need.
We were on holiday last year on the Isle of Skye and visited the island’s Coral Beach. The beach is made up of maerl rather than sand. Maerl is the remains of seaweed washed up on shore and then their lime rich tissue is bleached by the sun. Crofters used this calcified seaweed as a way of liming their land whilst adding nutrients to the soil. Calcified seaweed is still available but it is often collected from the seabed by dredging and so is damaging to the sea environment. Some calcified seaweed is more sustainable than others so it is always worth checking with the manufacturer as to the provenance.
Scientific study has shown that the beneficial effects of seaweed include increased resistance to frost damage and attacks by pests. It can improve the condition of clay soils and if used as a mulch around the base of plants the salt content can deter slugs (taken from Flora Celtica). Seaweed has been very important to the potato farmers on Jersey since the 12th century. They had the right to collect seaweed and spread it on their fields and it is believed that it is the seaweed that gives Jersey potatoes their distinctive flavour. Perhaps more importantly it is thought that the chemical compounds in seaweed can suppress eelworm a nematode that lives in the soil and attacks potato tubers burrowing into them.
The RHS says it is not necessary to let fresh seaweed rot down and it is actually best dug into the ground fresh. I always thought the salt content of seaweed would be damaging to plants but the RHS says that the content of salt is usually not high enough to damage crops or the soil. It does point out however, that there is no public right to collect seaweed from the shore and that you should get permission of the landowner before filling your car-boot.
I have used seaweed meal, which is seaweed that has been crushed and then dried, on the soil on my allotment and in my garden as a soil conditioner. Apparently it helps to build up the bacteria in the soil that break down organic matter and worms are rather partial to it too. I also like to use liquid seaweed feed, spraying it onto the leaves of plants. The nutrients are absorbed really quickly by the plant this way and is especially beneficial for any sickly looking plants that need a bit of a boost. Taking a tip from Monty Don, on Gardeners’ World last year, I sprayed my box balls that weren’t looking too good after the harsh winter with seaweed feed once a month and they soon had lovely dark, glossy green leaves.
It is possible to get dried seaweed pellets from a company called The Natural Gardener. The seaweed is harvested sustainably on the Shetland Isles and is then dried and bagged up. The pellets can be mixed into a compost heap, sprinkled around established plants or put in the bottom of your potato trenches. I know I’d much rather use a natural, sustainable product such as seaweed than any chemically produced fertilisers.