Homemade plant food, what actually works and what does not

Kitchen scrap fertiliser is all over the internet and most of what is written about it is half right, which is the most annoying kind of wrong. The scraps genuinely do contain what people say they contain. The bit that gets left out is how slowly it becomes available to a plant, and that is the difference between a useful habit and a disappointed gardener wondering why the tomatoes did not respond.

So here is what each one actually does, and then the recipe, because it is still worth doing.

What is really in your scraps

Banana peels

Genuinely high in potassium, which plants use for flowering and fruiting. The catch is that a peel has to break down before any of that is available, and a peel buried next to a plant takes months. Chopped up and composted it is excellent. Buried whole as a quick fix it mostly just attracts things.

Used coffee grounds

They hold nitrogen and they improve soil structure as they break down, and worms genuinely do go for them. Two things worth knowing. Spread thick and wet they cake into a mat that water runs straight off, so keep the layer thin or mix them in. And the acidity people worry about is mostly in the coffee you drank rather than in the used grounds, which come out closer to neutral.

Best use by a distance is straight into the compost.

Eggshells

Calcium, and this is the one where the gap between the claim and the reality is biggest. Eggshell breaks down very slowly, in months to years depending how finely you crush it, so it is a long term soil amendment rather than anything that helps this season.

It is also worth saying that blossom end rot on tomatoes, which eggshells are always recommended for, is usually not a shortage of calcium in the soil. It is the plant failing to move calcium up to the fruit, and that is normally caused by uneven watering. Consistent watering and mulch will do more for it than any amount of eggshell.

Epsom salt

Magnesium sulfate. If your soil is short of magnesium it helps, and if it is not, it does nothing useful and you are better off not adding it. This is a good argument for testing the soil before you start adding single nutrients to it.

A liquid feed worth making

This is a gentle supplement rather than a replacement for a balanced fertiliser, and it is a good way to get value out of scraps between compost batches.

  • 1 banana peel, chopped small
  • 2 tablespoons of used coffee grounds
  • 1 finely crushed eggshell
  • 1 litre of water
  1. Put it all in a jar with the water and leave it somewhere shaded for a day or two.
  2. Strain it, and tip the solids into the compost rather than the bin.
  3. Water it onto the soil around the plant, not over the leaves.

Once a fortnight is plenty. Make it fresh each time, because left standing in the sun it goes anaerobic and then it smells like something died in the shed, which it more or less has.

The honest summary

Kitchen scraps are a soil builder, not a fertiliser. Over a few years of composting them your soil holds more water, feeds better and needs less help, and that is a genuinely big deal. What they will not do is deliver a known amount of nitrogen to a hungry tomato in the week it needs it, because you have no idea what is in your mix and neither do I.

Do both. Compost everything you can, and keep a bag of something balanced for when a plant is actually hungry. That is not me selling you fertiliser, it is the reason the bag has numbers on it and your banana peel does not.

Shop related products

The garden centre carries the Brunnings and Neutrog range along with mixes, pots and tools. What is online sits in garden products and Neutrog.

More on feeding a garden

I buried banana peels around a rose bush for a whole summer and the only thing that noticed was the dog.

Cheers,
Candeece

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