Did you know that you can water some plants with coffee? It’s a weird one, but it makes sense when you look at the science behind it.
We know that a few plants love coffee grounds, but watering plants with coffee is a different approach to simply mixing the grounds into your compost or mulch. I don’t mean water with pure coffee – that’s a little bit too far – but you can dilute leftover coffee with water and feed it to your acid-loving plants in moderation, with a small number of benefits.
‘While used coffee grounds have their place in the garden, liquid coffee should be used much more cautiously,’ says Andrew Jackson, award-winning garden writer, designer and creator of The New Build Manifesto. ‘Most plants simply don’t need it, and too much can alter soil chemistry or inhibit growth. If you do want to experiment, only use heavily diluted, black coffee occasionally and only on acid-loving plants.’
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Here’s a list of plants you can water with coffee, with a few additional tips from the experts.
Acid-loving plant essentials
Levington
Peat-free Ericaceous Compost, 50L
Whitefurze
Water Butt and Kit, 230L
Acid-loving plants like rainwater, so start collecting it!
Garden Tutor
Soil pH Test Kit (3.5-9 Range) | 100 test strips
Make sure your soil is the right pH!
1. Camellias
I didn’t expect to see camellias on a list of plants you can water with coffee, but it actually makes a lot of sense given their origins. They’re acid-loving plants that glean a few benefits from the properties coffee has to offer.
‘These woodland shrubs thrive in acidic, humus-rich soils,’ says Andrew. ‘A very occasional application of diluted coffee may provide a small nutrient boost alongside organic matter.’
Of course, coffee isn’t a substitute for other fertilisers and composts, and Andrew says you should always focus on improving the soil with leaf mould or ericaceous compost first. Levington Peat Free Ericaceous Compost from Amazon, for example, will provide your camellia with the conditions it needs to flower well.
‘Coffee should only ever be an occasional supplement, not a replacement for good soil preparation,’ Andrews adds.
2. Rhododendrons
Rhododendrons are another woodland plant that thrives in acidic soils, so they’re suited to occasional watering with coffee, too.
‘Coffee grounds are best for acid-loving plants like rhododendrons and azaleas, as they prefer slightly more acidic soil,’ says Jo McGarry, luxury garden design expert from Caragh Nurseries.
‘If you’ve got leftover black coffee, you can use that too, but let it cool completely and dilute it with water first. I’d avoid using coffee with milk or sugar in the garden because it can attract pests and encourage mould.’
There are a few other ways to use coffee grounds in the garden, too, from composting to keeping pests at bay.
3. Blueberries
If you’ve ever learned how to grow blueberries, you’ll probably remember that they’re an acid-loving crop – so it makes sense that you can water them with coffee.
‘Blueberries thrive in acidic soil, and watering with coffee can help to maintain an acidic soil pH while providing the plant with a small boost of nitrogen,’ says Richard Barker, horticultural expert at LBS Horticulture.
‘Only water blueberries with coffee weekly or once every two weeks, as the high acidity can begin to harm the plant over time. Do not give blueberries undiluted coffee, as it needs to be watered down to a 1:1 or 1:2 ratio of water.’
There are other, arguably more effective, ways to maintain a healthy pH for your blueberries, though.
‘If you’re growing blueberries in containers, continue using ericaceous compost and rainwater wherever possible,’ says Andrew. ‘These will have a much greater impact than coffee.’
4. Hydrangeas
It’s semi-common knowledge that you can keep a hydrangea blue or red according to the acidity of the soil, so it makes sense that some hydrangeas already tolerate soils with a lower pH – and that’s exactly what watering with coffee can achieve. Just don’t expect huge results.
‘Hydrangeas growing in naturally acidic soil can benefit from the occasional application of diluted coffee, as they prefer a lower soil pH,’ says Andrew. ‘However, coffee alone won’t dramatically change flower colour, so don’t rely on it to turn pink flowers blue.’
Andrew recommends using one part cooled black coffee to four or five parts water, no more than once a month during active growth.
5. Roses
We recently talked about the benefits of coffee grounds for roses, and although you shouldn’t water them with coffee directly, you can actually make your own feed using leftover grounds and water.
‘Make your DIY liquid fertiliser by steeping two cups of used coffee grounds in five gallons of water overnight, and then straining to remove any solid particles,’ says Lucie Bradley, gardening and greenhouse expert at Easy Garden Irrigation. You’d then dilute this concentrate with water, using a ratio of 1:1.
‘Your coffee ‘tea’ will mainly provide nitrogen and trace amounts of potassium and phosphorus, but your roses also need additional phosphorus and potassium, plus iron and calcium, to thrive, so it should only be used alongside other feeds to ensure your roses receive the full range of nutrients they require,’ says Lucie.
Miracle-Gro Premium Rose & Shrub Continuous Release Plant Food, which you can buy from Amazon, can be used between March and September to give your roses the nutrients they need to thrive.
So, you can water plants with coffee – but only if they’re acid-loving, and you water black coffee right down!
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