Make your own plant food for (almost) nothing

I only have a few potted plants at home but like all plants sometimes they need to be fed, not only watered. Newly bought soil usually has fertilizer (compost) added to it but after about 6 weeks have passed since planting you have to start adding some liquid plant food to the water tray on a weekly basis. I like organic fertilizers because they contain plant-derived nutrients and not chemical compounds.

But organic plant food can be pricey – for example a liter of Organic Liquid Seaweed fertilizer currently costs £7.49 on So in this post I am going to show you how to make liquid fertilizer for just the cost of a kilo of brown sugar.

Here I am using a bunch of seaweed I gathered at the beach last weekend, but you can use any green plant matter that you want (except legumes). Examples: grass cuttings from your lawn, nettles or other green weeds gathered in the forest, or even some spinach or kale bought in the supermarket. The last option is going to make it a bit more expensive, but if it is the middle of the winter and you can find nothing green outside, then go for it.

What you will need:

  • 1kg green plant materials
  • 1kg brown sugar – light or dark brown are both ok. Or white sugar and molasses (mixed in proportion of 1-2 spoons molasses for every cup of white sugar)
  • 4.5 liter water
  • large bucket with a lid (I am using an old enameled pot)

Here is my seaweed which is my preferred green to use as a fertilizer because of its abundance of minerals such as magnesium and iodine. 


By the way, if you have a garden or allotment you could just spread the seaweed on the beds between your plants and let the earthworms take care of it. If all you have is plants in pots, then you have to turn seaweed into liquid plant food first.

And now the recipe:

1. Put your plant matter into the bucket and then dump the sugar in. Now pour the 4.5 liters of water and mix well to dissolve the sugar. This is how it should look.



2. If you want, you can fit a plate inside and weigh it down with a stone or something. It will prevent any mold from forming on the top. I didn’t do it this time but it worked anyway. Now cover your pot and place it somewhere dark and cool for at least one week. Once I kept it for over a month (because I completely forgot about it) – but no worries, it will smell even worse but will be still okay to use!

3. After 1 week has passed, it is ready to be strained and poured into bottles. Seaweed fertilizer usually smells real bad, and so does spinach. But once I made it with nettles and the aroma was quite nice, beer-like. In the end, it does not matter if it smells and looks repellent, your plants won’t mind. 

Strain it through fine mesh sieve. Then strain again to make sure there is no plant bits left which would later float to the tops of your bottles and mold. Throw out the plant material or compost it.


The end result will be dark brown liquid the consistency of single cream. Pour into glass bottles, put the lids on and keep in a dark, cool cupboard. I don’t know how long it can keep but i kept mine for about 5 months until it finished and it was still usable at the end of that time. 

To use, dilute 1 cup of fertilizer in 4.5 liters of water. Use once a week. It is a general purpose fertilizer suitable for most plants, outdoor and indoor alike.



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