By Ruth Doherty published
When you think of a coffee and garden pairing, it's usually along the lines of a warming morning brew al fresco while enjoying the weekend papers. But if you've ever wondered 'are coffee grounds good for plants?', the answer is a resounding 'yes – using coffee grounds in the garden is beneficial to plants'.
'These properties make them perfect for garden activities, such as composting. It’s an innovative way to make use of something that would otherwise have ended up in landfill.'
Using coffee grounds in the garden
So, we've established that coffee grounds are good for plants. Indeed, using recycled coffee grounds is a great way to reduce waste and boost your blooms at the same time.
See how used coffee grounds can help boost your plants with our expert tips below.
How to use coffee grounds as fertilizer
Did you know that your coffee grounds can actually be used as a slow-release fertilizer?
'I always use coffee grounds as fertilizer,' says James Gray, founder of Barista & Co. 'Some size of grounds can’t go down the sink, so giving them to your plants is a great way to reduce waste.'
Lewis Spencer adds: 'To use coffee compost, simply sprinkle the grounds directly onto your soil and lightly rake it in. Coffee grounds add organic material to the soil, helping water retention, aeration and drainage.
'Leftover diluted coffee can create a liquid plant fertilizer, too. Simply mix two cups of brewed coffee grounds with five gallons of water in a bucket overnight.'
How to make compost with used coffee grounds
If you are investigating how to make compost, add coffee grounds to your ingredients.
'Scientists state that a balance of "greens" and "browns" is needed to create the proper environment for composting to occur,' say the plant doctors at Patch Plants.
‘Greens' are nitrogen-rich materials that are used by microorganisms in the soil for their growth and reproduction, and 'browns' are carbon-rich materials used to feed microorganisms and give them energy.
'Greens' include items like fruit and vegetable peels, and used coffee grounds. 'Browns' include items such as dried leaves, twigs and newspaper.
'When mixing green and brown together you should remember the ratio 1:4 (1 part green, 4 parts brown). If you have too much green material your compost pile will start to smell (a bi-product of microorganism reproduction is ammonia). If you don't have enough green material, the compost pile won't heat up because the microorganisms don’t have enough energy to do their thing.
'After about three months your old coffee grounds will have been transformed into nutrient-rich compost giving your plants a much needed boost.
'Remember to mix your compost thoroughly. If you leave coffee grounds on the surface of the soil, without raking them in and exposed to the air, they can dry out. Dried-out coffee compacts and will act as a barrier, preventing water from reaching the soil beneath. So mix-mix-mix and wait.'
If you practise vermi-composting with a worm bin, coffee grounds are a must as worms love them.
For a small bin, add a cup of grounds per week to feed their addiction. Avoid adding too much at once because the acidity could negatively impact your worms. Paper coffee filters can even go in too.
Which plants like coffee grounds?
'Coffee grounds have a varied amount of essential nutrients in each batch, but they all contain nitrogen, potassium and phosphorus alongside micronutrients,' explains Lewis, talking about soil health.
The plant doctor at Patch Plants says: 'It seems as though all plants will enjoy a coffee compost, provided it's been done correctly (4:1) and it's not just plonked on the top of the soil where it's left to harden and prevent water from entering the soil.'
Are coffee grounds good for hydrangeas?
Your hydrangeas will definitely get a bloom-boost from your recycled coffee grounds.
James Gray says: 'Coffee makes the soil more acidic and is packed with nitrogen, which hydrangeas go wild for, making them become super bright and colourful.
'Essentially coffee is a fruit, so think of the amount of nutrition the soil gets from things like dropped apples and berries as this works in the same way.'
Are coffee grounds good for grass?
Your grass could be greener – and longer – with the addition of coffee grounds in the soil.
James Gray comments: 'Try mixing them through the soil in your indoor plants, or if you collect a larger amount, sprinkle them in grassy areas for a little growth boost.'
Are coffee grounds good for roses?
The high nitrogen content makes used coffee grounds a good growing companion for roses, as it helps take the pH from neutral to acidic – you can find out about how to test the pH of soil in our guide.
Some experts suggest that you can sprinkle your coffee grounds in the soil next to the plant, but others warn that you should be careful not to put too much on as the high nitrogen content could actually burn – and kill – them. Do not use more than a cup for each bush.
Alternatively, you could mix one cup of grounds with one gallon of water per bush and use this mix to water the plants so your roses are particularly bright and beautiful. And you can also use your coffee compost if you have made some.
Do coffee grounds deter slugs?
Lewis Spencer says: 'Research shows that caffeine is effective in repelling slugs and snails when applied to foliage or the growing medium of plants. This is because of the naturally abrasive properties of coffee: soft critters tend to avoid rough surfaces.'
Ruth Doherty is an interiors writer who has worked for Homes & Gardens and Ideal Home magazines among many others.
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