A Little Kelp From My Friends: How to Make Liquid Seaweed Fertilizer

Yesterday, we started our very first batch of liquid seaweed fertilizer.

As relative newcomers to gardening, we can be delinquent about (because we’re intimidated by) fertilizing. Maybe that’s why we’re so attached to our carnivores — because they infamously self-fertilize?

But we’re coming around. We recently discovered our garden pond as a way to feed our tillandsia; since then, we’ve been intrigued by fertilizing hacks that are both outside the box and right under our noses.

C on wagon duty, heading down the hill to the beach to gather seaweed.

Coastal gardeners from here to the Falkland Islands have been making DIY seaweed liquid fertilizer for ages. Using just water and beach-foraged seaweeds (like bullwhip kelp, sea lettuce and nori), you can brew a tea fertilizer that will fortify and stimulate your plants, via seaweed’s abundance of amino acids and trace minerals. It can also be used in compost and in mulch. According to Eartheasy, seaweed’s sodium content makes it a champion slug repellent.

When we arrived at Windansea yesterday, the tide was ebbing. Kelp beds stretched south toward the rocks. At the height of summer, we diligently avoid these tangled masses of sugar wrack and giant kelp that attract mobs of flies — not a good look while you’re trying to eat a sandwich, play paddleball and drink a smuggled-in cocktail. Today, though? We couldn’t have been happier to see them.

Looking north at Windansea Beach. Seaweed accumulation is spotty at best.

Looking north up Windansea Beach, we noticed the algae was scarce. (Most of the flora were in the form of iceplants.)

Looking south at Windansea Beach; seaweed is abundant.

Heading south on Windansea Beach, the seaweed was abundant.

We (1) scooped up seaweed by the handful, targeting clumps that were washed up in shallow tide pools and still wet.

Note: you should check with your local beach/parks department re if it’s actually legal to remove seaweed for personal use. Also, take only modest amounts; don’t go nuts. The daily limit in California for personal use is 10 pounds wet weight, as long as you stay out of aquatic parks and refuges. Cutting away eel grass, surf grass and sea palm is prohibited.

Once our Rubbermaid was full, we packed up our beach wagon and headed home to start our bitchin’ brew.

This seaweed is fully washed up from the last high tide. We prefer to take directly from tidepools to assure freshness.

If it wasn’t for the official start of June gloom in San Diego, this seaweed would have been basking in the sun for hours since the previous high tide. Harvesting from shallow and sandy tide pools is ideal to assure freshness and safety.

Seaweed Fertilizer



C lends a kelping hand.

We're not the only one's pumped up about the harvest.

We weren’t the only ones pumped about the harvest!

Back in the wagon.

Back in the wagon.

RB steps in to man the hill.

RB steps in to scale the hill.

Couldn't pass up our favorite street orchids. If you're a local it's La Jolla Blvd and Bonair Street.

We couldn’t pass up a shot of our favorite street orchids. If you’re a local: they’re at the intersection of La Jolla Boulevard and Bonair Street.

After (2) rinsing off the seaweed, we (3) refilled its container with water and covered it. Over the next few weeks we will (4) stir the seaweed/water mix every few days, before it’s time to (5) skim off our liquid seaweed fertilizer as needed.

This tea can be applied to the soil or sprayed onto foliage as a foliar feed.

We examine our harvest to make sure we didn't bring home any crabs or non-biodegradables.

We examined our harvest to make sure we didn’t bring home any critters or non-biodegradables.

Rinsing this way can be timely for a batch this big.

Rinsing this way can be timely for a batch this size.

Recommend rinse method; fill, stir and drain one time.

So we switched to our recommended rinse method: fill, stir and drain.

Fill with tap water just enough to cover the seaweed.

To start your fertilizer tea, fill your container with just enough water to cover the seaweed.

We've covered the crop loosely. Check back with us in 2-3 weeks!

Next, cover the container loosely and stir every few days. In the summer, the liquid seaweed fertilizer (aka tea) should be ready in two to three weeks, and in the winter, up to three months.

Stay tuned for updates on how this liquid seaweed fertilizer plays with our plants!

Hat tip to Carla Bassi at Green Fresh Florals for turning us on to this idea, and to Rawganique for additional guidance.