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The following how-to on gardening with seaweed comes from HOMEGROWN member Mary, a dirt-under-her-fingernails city slicker from the seaweed-rich Sunshine State, and Justin, a fellow Floridian with an equally strong love of gardening. For more tips from Mary, visit her blog, Back to the Basics. Mary and Justin, thank you both—and please keep the good ideas coming!



Seaweed? Really? The thought of it brings to mind fishy odors and the slow, salty death of my garden. But it turns out that if you live near the shore, you have access to one of the most beneficial ingredients Mother Nature can add to your garden. The Irish and Scottish have been using "ocean's grass" for hundreds of years to supplement the poor soil of the highlands’ rocky plateaus. Farmers would plant their seed potatoes directly in seaweed then cover it over with a thin coat of sand.

So, how does it work? Seaweed contains more than 60 different nutrients and elements. That's right: I said 60! Besides nitrogen, phosphorus, and potassium, seaweed contains calcium, copper, iron, magnesium, molybdenum, sulfur, and zinc. Many of the earth's minerals are dissolved in the ocean, and with the agitation of the waves and currents, drifting seaweed has access to these minerals. After nitrogen and potassium, the amounts drop off, but the benefits go beyond the nutrients alone.

In fact, the best thing about seaweed isn’t the chemical compounds it contains but how it uses those compounds. Seaweed has developed immunity to the bacteria, fungi, and viruses of the sea, and it is thought that, when you use seaweed in your soil or compost, your plants will absorb this natural immunity, as well. (Seaweed stimulates decomposition, breaking down other elements into simpler elements, allowing the plants in your garden to absorb the goodies.)

Seaweed also promotes rapid growth. In its natural habitat, seaweed is under constant barrage from rough waters and hungry sea animals. In order to keep up with its environment, seaweed regrows extremely fast, thanks to all those beneficial elements. The thinking goes that your plants will absorb these natural "growth regulators," making them more productive, and—bonus—that seaweed will help lock nutrients into your compost pile, preventing washout.

The only cons I’ve seen are that seaweed doesn't like heat greater than 115 degrees F, and you have to wash it before use. But that’s not much to ask for something so nutritious and therapeutic. The next time you're on the beach and see seaweed washed up on the shore, grab it—with permission, of course! (Mary adds: “It's important that you observe state and local laws. Many protected beaches do not allow people to remove anything from the shore or the water.”)



This morning I got up early—free parking before 8 a.m.!—and went down to the beach with two grocery bags and a big plastic bin. I picked the freshest seaweed that was just washing up on shore, and I kneaded it a bit, to dislodge any tiny sea creatures that might be entangled. After five minutes, both of my bags were full of nutritious seaweed.

Once home, I cleaned the seaweed—a crucial step before using it in the garden. To clean your foraged seaweed, just lay an old towel on the ground and spread the seaweed over the towel. Turn on the hose and rinse the seaweed, picking up larger chunks to rinse them more thoroughly.


1. Fertilizer. Seaweed tea is easy to make: Fill a 5-gallon bucket about one-fifth of the way with clean seaweed then finish filling with water. The tea can be stored up to three months but is best within four weeks. Apply the seaweed tea to your plants’ roots. Avoid splashing directly on leaves and, as with any fertilizer, do not overuse. Seaweed tea works great for heavy feeders such as tomatoes, peppers, and squash.

2. Mulch. I use all types of organic material for mulch, from dry leaves to store-bought bark to seaweed. Mulch works to keep down the weeds, retain moisture, and protect close-to-the-surface roots, and as it decomposes, it naturally feeds your plants. To mulch with seaweed, apply it directly to the topsoil.

3. Pest control. While it hasn't kept the neighborhood cats out of my garden, seaweed means I have few snails and slugs.

4. Compost activator. If you have a compost pile or bin, seaweed is your friend. Add it in! Seaweed helps activate the compost and adds beneficial nutrients. (For more on the benefits of compost and how to create your own pile, check out the Composting 101.)


Got another use for seaweed? Or a question for Mary or Justin? Post it below and keep the conversation rolling. You might also check out the 101s on composting, compost tea, and how to build a compost bin. If you’re a coastal dweller, you might consider joining the South Florida Sub/Urban Agriculture group, the Miami, FL, Friendly Farming group, or another seaside group where you can trade tips on seaweed sweet spots. You can always find more things to plant, grow, make, craft, cook, preserve, and compost in the HOMEGROWN 101 library.



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I am honored to be included in this Homegrown 101!  I love and respect the beach.  Mother nature provides vital nutrient for our garden and our bodies!

Mary: And HOMEGROWN is honored you're here! Thanks again for the excellent help.

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