A stroll on the beach can be good for the garden – just ask Marie Merkel, an experienced vegetable grower in Surry.
Once in a while, she’ll fill a shopping bag or two with dried seaweed that washed up above the high tide line to bring home and add to her compost pile.
“It feels like when I started doing that, I ended up with a much richer compost,” said Merkel, who cautioned that she’s not a scientific gardener.
She also adds shells to break down in the pile over time and uses a layer as a mulch, covering the ground to retain moisture and slowly add nutrients.
Merkel is part of a long tradition of effective growing techniques used along the coast using resources including fish waste, shells and seaweed to improve soil structure and add nutrients for growing crops. Such materials can also be more sustainable and reliably available than conventional fertilizers mined and shipped long distances, according to advocates.
Coastal farmers have long added seaweed, typically rockweed, to soil and used it as animal feed. It’s a source of natural compounds called biostimulants that help crop performance, numerous minerals and small amounts of common fertilizer elements such as nitrogen, phosphorus and potassium.
Articles in Bangor Daily News archives have mentioned its uses for more than a century. A 1976 story featuring what’s now North American Kelp in Waldoboro, a producer of seaweed-based fertilizers and animal supplements, referenced a “growing army of organic farmers” in Maine going back to such methods.
“The new generation of ‘eco-farmers’ who have rediscovered the methods of farming used a few generations ago already use seaweed for their gardens as a fertilizer,” the article said.
Maine’s famous back-to-the-land beacons, Helen and Scott Nearing, used seaweed to help create productive gardens in Brooksville’s tough coastal soil. So did Eliot Coleman of neighboring Four Season Farm, who has written a number of books on organic gardening.
Indigenous growers traditionally buried fish parts below crops, and seafood shells add nutrients and calcium as they break down. Those can be harder to manage as DIY projects, but are also available pre-prepared.
Samuel Cheeney, who now makes and sells fertilizer from invasive European green crabs, started out learning to use seaweed from older friends around Milbridge, both back-to-the-landers and multigenerational Mainers.
Cheeney, an organic farmer at the time, was enamored with the composting process and started adding seaweed and seafood shells scavenged from local processors.
They were local and free, compared to the fertilizers he bought from elsewhere – which are among the high costs that later led him to leave farming.
“In my mind, the ocean has all of those things,” Cheeney said of the nutrients farms need.
But his primary motivation for turning to the sea was environmental: widespread commercial inputs such as phosphate are finite resources mined from the ground and shipped long distances using fossil fuels.
High costs for conventional fertilizers from global markets impacted by the war with Iran are now crunching farmers in Maine and across the country. Last month, a Farm Bureau survey found that 69% of Northeast farmers couldn’t afford the fertilizer they needed.
An avid fisherman, Cheeney also started catching invasive green crabs – which prey on Maine’s soft-shell clams and mussels, and may threaten lobsters – and grinding them up, turning shells into meal and collecting the juice for liquid fertilizer.
Economic pressures on his farm, combined with the idea of finding a valuable use for an invasive species that would help incentivize controlling them, led Cheeney to make it a business.
He started selling the meal under the brand Green Kraken in late 2023 and is bringing the liquid to shelves this month. Someday, he hopes to have local fertilizer plants every 30-60 miles along the coasts; gardeners who use the product report big improvements, he said.
Fish parts are more challenging to manage in home compost, though fish-based fertilizer is commonly available commercially. Shells similarly need more careful attention.
Cheeney added them to compost rather than leaving them whole in the soil to reduce the risk of nitrogen runoff. Adding carbon materials helps control that and manage smells, he said.
“It’s all about balance,” he said. “Same thing when it pertains to actually applying it to the garden.”
For those who compost seaweed, the University of Maine Cooperative Extension recommends mixing it with lighter materials in the fall like straw, leaves or sawdust at a ratio of one to three.
It can also be put on the ground to decompose or break down cover crops. Unlike grass or straw, it’s free of weed seeds, and when dry its spiky nature can deter slugs.
Tilled in, it can also help loosen dense or compacted soil while feeding helpful soil bacteria. Or, soak one-third or two-thirds part seaweed in fresh water for several weeks to make a “seaweed tea” fertilizer to put on plants, diluted one part to 10 parts water.
Maine Coast Sea Vegetables cautions against collecting it in heavily populated places or around potential pollution sources, as seaweed absorbs toxins from seawater.
People can also cut less than 50 pounds of seaweed a day from 16 inches or more above the base without a license, though some environmentalists raise concerns about harvests reducing marine habitat.
Merkel, the Surry gardener, started collecting detached, washed up seaweed decades ago after learning about it from publications like Mother Earth News and the Maine Organic Farmers and Gardeners Association. She’ll wait until it’s dried after a rain, to minimize lingering salt.
At home, she adds a layer to her compost pile in a method called slow composting, which breaks down gradually and doesn’t need to be turned. Merkel will also toss in mussel shells, crabs and other pieces of the sea lingering in what she collects.
Bagged composts with sea components are popular locally, she said, such as Coast of Maine, which markets various blends incorporating elements from seaweed to crab shells.
But Merkel’s hesitant to buy from plastic bags and considers herself more of a do-it-yourself type.
She’s also president of her town’s garden club, where members are using diluted “Neptune’s Harvest” fish waste fertilizers on native plant seedlings they’ll plant for a “pollinator pathway” around the village.
The sea provides a “wonderful, natural gift” of seaweed to be protected and used wisely, Merkel said – and it’s also just pleasant to gather.
She visits the shore anyway to look at shells and rocks, finding interesting things in the seaweed like feathers and baby crab shells.
“Who wouldn’t want to go to the beach?” she said.
