Seaweed Fertiliser

17 Apr 2020

The only fertiliser I use

So yes, we are creatures of habit and though I may need to add some differently composed fertilisers to my cupboard I really haven't felt the need to until recently. As much as I love this stuff, I've had a few problems with it recently when I tried it as a foliar spray (granted, it may be my technique).

To be clear, I only use the store-bought brands. I'd love to use fresh kelp, but even when I lived close to the beach I didn't have the time or the space to DIY my fertilisers. This goes for compost tea as well - there's only so much space on a tiny balcony. Regardless I've left some links at the bottom for those of you who're interested.


Liquid seaweed extract: I have no idea of the manufacturing process used, but the RHS website states that seaweed "has been used as a soil improver for centuries, particularly in coastal areas" and that seaweed "is rich in trace elements (nutrients that plants only need small amounts of) including iron, manganese, zince, copper and boron, which are often lacking in common fertilisers such as Growmore and fish, blood & bone."


I've only ever used the liquid, and usually this is sold in a concentrated form. Your ratio should be 1:15 if you're using it for mature plants in soil, other uses are given on the packaging itself.

I've used these products for so many years that I don't bother reading the instructions, which makes me think I MIGHT be suffering from overconfidence.


Your seaweed extract solution can be sprayed all over the plant leaves (using a tiny squirt of dishwashing liquid as a surfactant) as well as watered into the soil.

Here is where I'll introduce my bad experience

I used seaweed extract on a 1:15 ratio as a foliar spray for a sensitive plant which looked to be suffering from a potassium deficiency. The plant improved slightly with 3xdaily sprays (in the shade to prevent leaf burn). After a few days the plant went into a rapid decline. I immidiately washed down the leaves with clean water and after a few days the plant recovered although with visible damage.

I am willing to accept that the mistake was one of the below, but from my understanding seaweed is not the kind of fertiliser to give your plants nutrient burn or to be overloaded with salts. Next time I'll be way more careful.

  • Spraying to frequently
  • Mixing the solution with too much liquid soap
  • Allowing clogged leaves by not rinsinging/wiping them down post-spray
  • Misdiagnosing the ailing plant