The top 4 eco-hacks to reuse coffee grounds for gardening

plant growing

You just relished the last sip of your favourite CoffeeHack blend. We can see you clean up your machine and...

Stop right there! Please don’t throw the leftover coffee grounds in the rubbish bin.


Because the spent coffee grounds will end up in landfill.

So, what? It’s organic, right?

Yes, exactly. Once landfilled, organic waste will release methane, which fuels global warming over 30x times more than CO2!

Sounds bad…but what to do then?

A good idea would be to use coffee grounds in your garden.

Ok, how?

Keep the coffee residue aside for a moment, make yourself a fresh cup and read on. CoffeeHack is about to unveil the top 4 eco-hacks to reuse coffee grounds for gardening.

SPOILER: for some of them, you don’t even need to have a garden!

Ready to hack yourself into the circular economy with coffee waste?

1st - Compost add-on

Compost is another word for natural fertiliser. Adding coffee grounds to a compost pile is a great eco-hack to speed up its production.

Being rich in nutrients (especially nitrogen), coffee grounds work well as a fertiliser. When feasting on these nutritious treats, the bacteria in the heap will turn organic matter into compost faster.

For top quality, studies recommend having 10-20% of coffee grounds in your compost heap.

Composting is one of the best uses for coffee grounds in your garden. And you can even do it inside your home.

If you don’t know how to do home composting, here are a few ways to keep brew residues (and filters too) away from landfills:

Just a colourful heads up. Although typically dark brown, old coffee grounds are called green compost.

Why is that?

The reason is they’re a lower-carbon material than brown compost (e.g. dry leaves, coffee filter paper).

Anyway, to avoid funky smells and maximise the hacking efficiency, make sure to use an optimal mix of green and brown compost.

2nd - Soil health enhancer

Spiking compost with coffee waste is not the only way to improve soil health. You can also add used coffee grounds straight onto the soil in your garden or lawn to get some extra perks.

The soil bacteria will slowly break down coffee grounds into their nutrients. These will then be available for plants over the long run. Besides this slow-release fertilizer, eco-hacking your soil with coffee grounds will have additional benefits:

  • Increase soil water retention
  • Attract earthworms (see vermicomposting)
  • Improve drainage

Coffee grounds will also work as organic mulch. Just mix them with other organic matter (filter paper and wood chips would do) and spread the mush on top of the soil. Doing so, you’ll limit weed growth, keep the soil wet in the dry season and warm in the cold months.

But stick with a layer thickness of no more than half an inch, otherwise water won’t get through!

Green thumb hack: Unlike fresh coffee, leftover grounds are not acidic. The acidic components in the coffee beans end up in your drink (don’t freak out, that's absolutely fine for most people).

Depending on which plants you want to grow, you’ll have to check the suitable soil acidity level.

For instance, you can grow most vegetables in a coffee grounds-rich garden. Yet, used coffee grounds are not good for acid-loving plants like hydrangeas or blueberries. For these species, fresh coffee would be a better choice (yet more expensive and less eco-friendly).

3rd - Mushrooms growth support

Yes, you read that right. Coffee grounds are a magic ingredient to spread mushrooms around. And we’re not talking about standard ones. Ironically, coffee waste can help produce an extremely valuable vegetable like gourmet Oyster mushrooms.

So, how do you make the magic happen?

Blend some mycelium (mushroom roots) with coffee grounds in your cauldron (any container would do).

According to the GroCycle urban farm, you’ll need 1kg of coffee waste for 100g of roots to grow mushrooms from coffee grounds. So, you’d better start piling it up or go to the nearest coffee shop. They might be happy to get rid of some spare grounds. Also, if you spice up your recipe with some straw, you’ll improve your yields. Not the one you use to drink iced coffee. You know the yellowish bales you see in a field. Yep, that’s straw.

Transfer your supernatural blend into a mushroom growing bag (a freezer bag may also do)   and leave it in a hot (18-25 °C) and dark place.

After 3 weeks, you should see the mushroom roots sprout out of the coffee grounds. Then, fresh air, a bit of light and water should do the yummy trick. Put your chef hat on and enjoy them in a Stroganoff, Thai curry or whatever you fancy.

4th - Eco-pesticide

By harnessing the green hacking potential of used coffee grounds, there will be plenty of plants and veggies in your garden. After all your hard work, you don’t want anyone or anything to mess it up, right?

That means you’ll have to guard your Eden from invaders sneaking into it. Slugs, snails, bugs…you name it.

Though, being eco-hackers, we don’t like chemical pesticides. Neonicotinoids are driving bee extinction. Having a similar structure to nicotine (that’s where the name comes from), they’re the most widely used insecticides in agriculture. Other than being lethal for bees, pesticides are also dangerous for human health.

What to use, then?

Well, another eco-hack for gardening with used coffee grounds is to leverage their natural properties to keep garden pests away from your lovely plants.

While only concentrated caffeine solutions kill slugs, scientists suggest coffee grounds can repel them.

So, just scatter the exhausted grounds around your plants to protect them from the slimy hungry attackers.

But caffeine can be lethal for insects too.

If you live near a river, lake on in the countryside, mosquitos may haunt you during summer evenings. The good news is coffee grounds may save you from being stung by mosquitos while enjoying your coffee in your garden.

There’s a ritual to get rid of this bloody plague…

  • Put the used coffee grounds in a bowl, cover them with foil and let them dry
  • Place the bowl in your garden on a flat surface and burn the dry coffee grounds (like you would do with incense)
  • Let the mosquitos-repellent scent spread in the air

…top up your coffee and chill!

Brew the coffee grounds up

There you go. 4 sustainable ideas to become a circular coffee hacker (and gardener!).

Waste reduction, healthy soil and plants, tasty vegetables, and fewer bugs. Used coffee grounds can bear awesome fruits for gardening.

Now that you know how to make the most out of your coffee waste, your CoffeeHack treats will taste even better.

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