Tea Time! We Serve Our Garden Homemade Liquid Kelp Fertilizer


You might remember a certain trip we took to the beach last spring, when we brought home a wagon brimming with several varieties of kelp.

That afternoon back in June, we combined approximately 10 pounds of rinsed seaweed with water inside a 10-gallon Rubbermaid tote and stirred well. Our goal: to brew a liquid kelp fertilizer tea we could use to feed our plants. We covered the container, and in the days and months that followed, we stirred occasionally (every two weeks or so) — even when the ammonia stench became so hellish we had to move it behind the house.

(Thankfully it wasn’t as bad as what’s happening right now inside this Prince Edward Island community.)

The stench of our brown-green brew is long gone, replaced by a pleasant accord of salty and sweet, kind of like a rosy ocean breeze. A sure sign this emulsion is ready to be used…

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In an attempt to deter the bugs that have been assailing our sage, we mulched some seaweed onto the soil.

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Seaweed is rich in amino acids and trace minerals and low in macronutrients like nitrogen and potassium. This might be all we can state with certainty here; while researching this story we wandered into the weeds of a few hot horticultural debates. For one, there’s a whole maze of arguments for and against fertilizing in the fall: the traditional wisdom of “tender growth spurts will be blitzed by frost” vs. “strengthening the roots of plants in late fall leads to robust springtime growth.” Secondly, you could get tennis-spectator neck from reading conflicting reports about the efficacy of seaweed and compost teas.

The jury is also out on the use of foliar sprays (that is, applied directly to leaves) like the one recommended for fertilizer teas. So we closed our laptops and tried it for ourselves.

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Here’s how we made our liquid kelp fertilizer spray:

1. First we siphoned the liquid kelp concentrate from our 10-gallon tub (in which we brewed ~10 pounds of seaweed with water over 5 months) into repurposed Trader Joe’s mineral water bottles. The bottles allow for easy storage and could also make great holiday gifts for likeminded gardener friends. Maybe we’ll design a custom label!

2. Based on some online guidance, we dialed in (and maxed out) our Gilmour No Pre-Mix sprayer to 8 ounces of fertilizer per gallon of water, a dilution ratio of 1:16.

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Bottling seaweed tea fertilizer concentrate for future use.

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The Gilmour No Pre-Mix sprayer attaches to your garden hose and is great for inline dilution.

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We set our sprayer to 8 ounces tea per gallon (128 ounces) of water, which equates to a 1:16 dilution ratio.

3. We attached the sprayer to our hose. The sprayer injects the set ratio of seaweed fertilizer into the water stream.

4. We sprayed the mixture onto the leaves and at the base of several plants, including our African iris, Summer Sky hyssop, kaffir lilies, fuchsia and nepenthes. It’s ideal to spray in the morning and evening, foliar feeding advocates say, because that’s when the stomata (the leaves’ “pores”) are most open.

We feel optimistic about this extra step we’re taking to support our plants. This weekend — a rare one free of human-based commitments — it felt so good to reconnect with our garden and listen to what it was trying to tell us. And it breathed “kelp me” right into our ears. —TH


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The African iris gets some sweet seaweed satisfaction.

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TLC is also showered on our fuchsia and inch plant.

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Ryan sprays our angelonia and hibiscus.

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The rehabilitation of our nepenthes continues.

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To come: custom labels! Who will be receiving a bottle of this pure Pacific gold for the holidays…?

  • I would recommend that you look at the Garden Professors website and their consistent rants about compost tea and foliar spray. In short, there is no scientific evidence that either compost tea or folia sprays.

    Their website is http://blogs.extension.org/gardenprofessors/ or try their FB group.

    • Thanks, Thad3! We look forward to reading the rants…

    • Averyfoto

      Foliar spray is 90% efficient vs 10% for root uptake. Proven by feeding the plants fertilizer with radio isotopes and tracking them through the plant.

      Seaweed/Kelp tea will act as an almost perfect hydroponic nutrient all by itself and it’s one of the cheapest fertilizers you can use. How did they disprove this?

      I would post links but if you want to learn you can research it yourself.

      Do these professors also believe the world is flat?
      Dinosaurs were never real?
      An invisible psychotic genocidal megalomaniac is in the shy?
      Do they own stock in Dupont?

  • Daniela Gálvez

    One question … the usefull life of the product in the bottle? a month? a year?


    • Hi Daniela, from what we’ve read, seaweed liquid fertilizer should have a shelf life of up to a year if kept undiluted and in a cool dry place with stable temperatures. But if it starts to smell funky before then, we would toss it.

  • ks

    any updates on how this worked out?

    • Ks! Sorry for the delay — we’ve been remiss in posting an update. We were using it for a good three months (to fertilize e.g. our air plants, the papyrus, the plants in our vertical shade garden) before it started to…well…smell ammonia-like again. So we’ve tossed it. But we’re ready to collect a new batch to use as a traditional liquid fertilizer, rather than a foliar spray. (And collect a little bit less, about five pounds.)

  • Lyeta Herb

    Peace do you think I can use dried powdered organic sea kelp to mix with water and get a similar result? Also when I go on the shore house do I know which sea weeeds are kelp?

    • Hi Lyeta Herb, we haven’t tried the dried, so can’t vouch for the efficacy — but it seems to be a popular option. Couldn’t hurt to try it. Kelp comes in many different forms (and has been bouncing back in numbers thanks to restoration efforts), so we figured the seaweeds on the shore were kelp. Not the most scientific of approaches, we know… (PS here’s a story about kelp washing up on shore in Southern California, with some photos of typical kelp you might find: http://www.ocregister.com/articles/kelp-640656-beach-beaches.html)

    • Averyfoto

      Put the dry kelp in pantyhose. Hang it from the middle of the lid. Fill the bucket with water that has sat for 24 hours. Put an air stone in the bottom and turn on the pump. Put it all together and you have tea in a couple of days.

  • Averyfoto

    Ummmm, dude…. Air stones….?