From coast to compost: A Tasmanian seaweed story
- Gabrielle Stannus
- May 9
- 6 min read
Heard about the benefits of using seaweed on your home garden, but not sure where to start? Why not buy a local Tasmanian product or, if adventurous, harvest your own! Here's how ...
Seaweed is one of my favourite foods to snack on, and your plants like 'eating' it too! There is plenty of this marine macroalgae floating around Tasmania (or used to be, but I will get to that in a moment), so it should come as no surprise that this state has several businesses built on this product.
I had the pleasure to meet Chris Russell from Kelpomix Tasmania at a marketing workshop held by the Northern Midlands Business Association this week. Chris and I got along like a house on fire; I like anyone who appreciates a good pun. If you have seen a bag of his product Kelpomix featuring not only kelp (seaweed) but also a kelpie (dog), well, you will understand what I mean! We got talking about the usefulness of seaweed on the garden, something Chris knows a thing or two about!
Chris harvests bull kelp (Durvillaea potatorum) from Granville Harbour on Tasmania's west coast. Chris says his business must abide by multiple regulations to ensure that bull kelp is harvested sustainably. He only harvests cast kelp as harvesting, cutting or pruning of living kelp is not permitted. Cast kelp is that seaweed which has detached from the ocean floor and washed up onto a shore. Chris estimates that less than 10 per cent of detached 'plants' wash ashore. This seaweed has accumulated nutrients washed out to sea, including minerals, amino acid builders and growth-promoting hormones that can benefit all plants.
At Kelpomix, Chris uses this kelp to produce a range of solid and liquid garden and farm inputs for dairy, beef, sheep, viticulture, cropping/hobby farmers and gardeners. I won't go into all these products now; however, I will flag those that may be of interest to the home gardener - you! Kelpomix has a Garden Mulch product that is suitable for gardens and lawns and can be used as both a compost and mulch. Kelpomix's Liquid Kelp product can be used as a soil drench and/or foliage spray. It also produces a Premium Potting Mix with added kelp.
Other Tasmanian businesses with seaweed products on the market include Seasol and Marrawah Gold. You probably have heard of Seasol. This business is now owned by DuluxGroup (Australia), the parent company of Yates, another well-known gardening brand. As far as I can find, Seasol still operates a manufacturing facility just outside Launceston. The iconic Seasol product is made from a blend of brown kelp, including bull kelp (Durvillaea potatorum) collected from King Island and Marrawah on Tasmania's west coast, Chile bull kelp (Durvillaea antarctica), and knotted kelp (Ascophyllum nodosum) sourced from the North Atlantic. This seaweed concentrate can be applied to the foliage and soil around a range of plants at the time of transplanting and planting including ferns, indoor plants, vegies, herbs, and annuals, as well as lawns and large/stressed trees.
Marrawah Gold is a local Tasmanian seaweed product made from bull kelp harvested on this island's north-west coast. Its 'Lawn and Garden' liquid product contains seaweed extract made from the stem (stipe) of this seaweed and can be sprayed on the foliage of a plant or used as a soil drench.
Collect your own beach-cast seaweed!
If you are an experienced gardener, you may like to collect your own seaweed to use on your garden. You are allowed to collect beach-cast seaweed for personal use on your garden if you meet the conditions laid out by Fishing Tasmania as follows. As a recreational harvester of beach-cast seaweed, you do not require a licence if you meet the following conditions:
Only take for private use and not for profit or commercial use.
Only take from public access beaches or where the landholder have given permission for beach access.
A daily limit of 100 kilograms per person per day.
No take from Marine Nature Reserves.
No take any seaweed that is in the water or attached to the seabed.
A tip from me ... Bull kelp is quite thick, so unless shredded, it may take some time to break down in a home compost if that system is not 'hot'. If you want seaweed that will decompose more quickly, then take the finer 'leaved' species that you find on the beach.
How to use beach-cast seaweed on your garden
Angus Stewart, former Gardening Australia presenter on ABC TV, is a more recently arrived Tasmanian who has written about using seaweed in the garden. Angus is a very experienced plant breeder so he knows his plant science! He says that seaweed extracts condition the soil with humus and supply small but useful quantities of nutrient as well. That is, seaweed extracts are not complete fertilisers but still very useful in your garden as they contain useful plant hormones and can increase root development. The latter reason is why liquid seaweed extracts are applied to seedlings when transplanting them from their pots into a garden. If you want to know more about the science behind seaweed's utility in the garden, check out Angus' article 'Using seaweed products in the garden' on his Gardening with Angus website.
Angus recommends washing seaweed clean of salt before adding it to your soil or compost heap, and to chop it up with a spade to hasten its decomposition. Whilst I must point out that the 20kg bag limit Angus mentions in this article is not applicable here in Tasmania (see above), I would still encourage you not to take more than you need. When speaking with Chris from Kelpomix, we both lamented the reduction in the bull kelp population along the east coast of Tasmania due to warming waters which are resulting in lower levels of nutrients and increased salinity, not to mention the arrival of the ravenous long-spined sea urchin which feasts on this algae. Whilst that is a story for another day, it is also a very important reminder to only take what we need.
Why not eat some yourself?
Why not feed yourself at the same time as feeding your garden? If you are at the beach planning to harvest some beach-cast seaweed for your garden, then consider collecting some for your kitchen too.
In 2023, Rees Campbell, aka the Feisty Tasmanian, wrote and published The Seaweed Supplement to complement her book, Eat More Wild Tasmanian. This publication is a very handy and informative guide to the who, what and how of edible seaweeds cast on Tasmanian beaches. Rees provides some very helpful advice on how to collect seaweed safely, along with some tips on how to use it in the kitchen. For example, bull kelp (palawa kani: rikawa) can be barbecued, its laminae (flat, leaf-like parts) cut up and cooked into stews as a vegetable, or cooked to a pulp and added to dishes. Rees says this seaweed is great in a kelp chutney.
Ludovic and I have collected seaweed from Tassie's north coast in the recent past to incorporate into our compost. We love doing this as it also means a trip to the beach; although trying to save fuel, we only ever really do this when we have another reason to visit the coast. That is not as often as we would like! So this weekend, I am going to do something a little different and pay a visit to my local hardware store (the one that does not start with 'B'). I will buy myself some Kelpomix to trial on our garden, thereby supporting a local business. Why not consider doing the same? Or if you are lucky enough to live near the coast, why not harvest your own beach-cast seaweed. The seaweed you gather will improve your garden, and the time spent in nature will benefit your mental and physical health and well-being. Enjoy!
À bientôt!
Disclaimer: I mention a few businesses and products in this blog, but just so you know—I am not affiliated with any of them, and I am not being paid or sponsored to promote anything. I am simply sharing what I have found useful or interesting in my own experience.
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