Using seaweed in gardening isn’t common in Croatia. In fact, I have never heard of or seen anyone using it.
As I was gathering bags of seaweed from our beach and spreading it across my garden, the neighbours stared with disbelief. Some laughed, some even complained. Eventually, some of them actually copied me as I explained the purpose of adding seaweed to the garden.
So, What Is The Point Of Using Seaweed In The Garden?
Apparently, seaweed should fertilise the soil. Indeed, It’s super rich in potassium, calcium, magnesium and iodine.
Also, it contains special “growth boosters”, substances that improve the overall health of the plants.
My initial plan was to use seaweed simply as a convenient MULCH. Our soil is quite sandy and rocky and dries out quickly in summer. Keeping the soil moist is a tremendous challenge. Since there is absolutely no hay or straw to find where I live, using seaweed seemed like a good alternative.
Not only does seaweed prevent drying out, as it decomposes, it makes the soil soft and sponge-like, increasing its ability to hold moisture.
Swiss chard (Beta vulgaris) naturally grows by the sea and benefits from the nutrients provided by the seaweed.
Following that idea, I applied seaweed on my Swiss chard.
Just look at the vibrant colour of the leaves. And keep in mind that this photo is taken in late December 2020!
Did Seaweed Really Work?
I started using seaweed as a mulch around my zucchini. I simply put an ample amount of brown seaweed around each plant.
I feared that the salt would harm them. But it didn’t. (Unfortunately, you have to trust me with this, since I made no pictures of it. I started this blog in August 2020 and only in December 2020 came to the idea to write a post about it).
So, the salt did’t harm the plants. However, the SNAILS did’t really like the taste of fresh seaweed. Especially when it’s dry and crispy. That was the first positive sign.
I have to admit that I didn’t use seaweed ONLY. I did use some leaf mould I got from the woods and added some dry chicken manure pellets. I also added small amounts of wood ashes.
The result? We have never had so many zucchini! Although I planted about a dozen plants, we would daily harvest about a kilogram of organic, fresh zucchini. And they went on and on! Of course, I kept removing the lower leaves to encourage new growth.
Because of the seaweed mulch, I could water the zucchini every other day, because the soil would retain water.
Apart from the zucchini, I applied the same mulch to mini watermelons and the squashes. Again, wow! Actually, I grew these in high summer, after I harvested the potatoes in June. Although the sun was relentless, the seaweed mulch seemed to have done a fine job, since (for the first time ever in our neighbourhood, where you traditionally DON’T GROW ANYTHING IN SUMMER BECAUSE IT GETS TOO HOT), I had a bumper crop of both watermelons and squashes.
“Mulching” an olive grove with stones in my Dalmatian village, Slatine. If you’d like to learn more about that village, please take a look at the articles I wrote about Slatine and its beautiful beaches.
Despite of their resilience, olive trees DO need water to produce olives, and, in turn, olive oil.
In Dalmatian summer, it often doesn’t rain for MONTHS!
The Experiment With Tomatoes And Eggplants In Containers
I really had high expectations from my container-grown tomatoes. I found 30 litre buckets, collected finest soil and mixed it with leaf mould, added egg shells and all… and applied generous seaweed mulch.
They were growing like mad… BUT… I made a mistake. In fact, series of mistakes. However, the most serious one was that I didn’t remove the side shoots.
So, no matter how nutritious the soil was, it simply wasn’t enough to sustain the healthy development of the fruits. Although I did harvest some San Marzano tomatoes, most of them were severely affected by the blossom-end-rot.
Eggplants, on the other hand, thrived in their buckets. Just thrived! (Sorry, no photos of them either).
The cherry tomatoes I planted in the garden were doing really well. Again, I mulched them with brown seaweed. I believe I would focus on cherry tomatoes in the future! They were doing so well!
Back to my poor container tomatoes… As I pulled them out, I noticed that the soil in the buckets became amazingly soft, just beautiful. All the seaweed vanished, being eaten by the earthworms.
As the seaweed mulch decomposes, the earthworms indulge in their new-found food.
Although you may come across some conflicting data online, my earthworms seem to thrive in “vintage” seaweed.
So I decided to, contrary to some advice, use that soil to grow autumn potatoes, a traditional crop in my area.
Potatoes Just Love Seaweed!
In fact, my wife ate (frankly, she loves potatoes more than she loves me) all of the decent-sized potatoes I was planning to (re-)plant in September, so I had to settle with tiny, cherry-sized potatoes and plant them in holes filled with the seaweed compost I got from my tomato containers.
On top of them I placed a layer of seaweed mulch.
Since September of 2020 was quite hot, I had to water my potatoes, and finally, they came out.
As they grew, I added more mulch (that I recycled from my squash beds) (dry seaweed is unbelievably long-lasting mulch).
Seaweed is notoriously long-lasting mulch. Gradually, however, it get eaten from underneath by the earthworms.
However, when you cover the seaweed with some soil, it decomposes much more quickly.
This is the seaweed I used as the mulch around my squashes, and then re-used on potatoes.
As they were growing, the neighbours became envious.
Finally, in December 2020 I started digging them out! I was amazed! The soil was full of earthworms (which never happened before), and the potatoes were HUGE. If you keep in mind that I didn’t use real seed potatoes, not even the regular sizes potatoes, but the tiniest ones, the result was great! The spuds were even, healthy, clean, … and delicious!
We fried them in oil, and they were amazing. Of course, we didn’t remove the peel, which made them even crunchier!
seaweed potatoes in December 
beautiful December seaweed potato spuds
In order to apply the same know-how to my spring crop of potatoes, I have already started taking bags of seaweed from the beach (you probably figured that out by now, I live by the beach. Sorry.) and dumping it over the future potato beds.
I realised that, in order to help plants benefit from all the minerals in seaweed, it needs to be decomposed. So, I have been covering the seaweed with dirt.
seaweed applied on the surface 
seaweed covered with dirt
I will keep you posted about the results.
In the meantime, look at other “beneficiaries” of seaweed in my garden!
Endive grown in seaweed 
Lemon tree mulched with seaweed