/ Food & Drink, Home & Energy

Can coffee perk up your garden?

While we were once a nation of tea drinkers, we’re fast becoming coffee addicts. So maybe it’s not surprising that while our grandparents might have put tea leaves on their plants, we’re now adding coffee grounds.

Even in these cash-strapped times, we’re not giving up our daily lattes and state of the art coffee machines.

So what can we do with all of those used coffee grounds? Apparently we can use them on our gardens.

A recycled coffee fertiliser has gone on sale at Notcutts (£9.99 for a 5L tub), and even Starbucks is giving away used coffee grounds for free.

I’ve long been familiar with the idea of putting coffee around plants to deter slugs (they don’t like the grainy nature of them, and they find the caffeine toxic), but had never heard of coffee being used to enrich soil.

How fertile is left over coffee?

I asked Guy Barter, chief horticultural adviser at the RHS, whether he thinks it’s worth us adding coffee to our soil or compost heaps:

‘It’s always nice to add fertility by using waste materials. A sprinkling [of coffee grounds] in conjunction with manure or compost should be fine. We’re talking very low levels of nutrients, but cumulatively added organic matter builds up and the nutrient addition is worthwhile.’

So there you have it – adding coffee grounds can only benefit your soil. The jury’s out on whether they deter slugs, though – when we trialled slug and snail deterrents at Which? Gardening we found that the coffee is too easily washed away by rain, and so it needs to be topped up regularly.

We also found that tea leaves are best put on the compost heap, rather than around your plants. Back in 2010, we looked at some old wives’ tales and found that it’s unlikely that much of the nitrogen in tea is actually available to plants.

Tea also contains aluminium, fluorine and manganese, which are harmless to people but high concentrations in very strong or stewed tea could stunt plant growth.

But, as with lots of gardening ideas, it’s a case of what works for you. What do you throw on to your compost heap or place around your plants?

Comments
Profile photo of wavechange
Member

My coffee grounds always go down the sink, which probably adds to the cost of processing waste water. In future they will go into the garden, whether they are of benefit or not.

Thanks for the suggestion, Veronica.

Member
Laurento says:
23 May 2012

Here in Italy it’s a good old tradition to use coffee grounds this way 🙂

Profile photo of hightownlady
Member

Thanks, good tip. Can woodash from the log burner go directly onto soil, around fruit trees or in the compost? We get a lot of it! But I think it’s very alkali? Thanks.

Profile photo of Veronica Peerless
Member

Hi Hightownlady
You can use wood ash around the garden, but you’re right – it is on the alkaline side. So you might not want to put it around acid-loving plants such as hydrangeas.

Member
Hilary says:
23 May 2012

In the US, branches of Starbucks offer free 5lb bags of used coffee grounds from little stands in-store marked ‘Grounds for your Garden.’ I used them for many years on my compost pile. Worked really well. And wormery worms love coffee grounds, too.

Profile photo of Veronica Peerless
Member

Hi Hilary
As I have briefly mentioned here (and in more detail in Which? Gardening magazine), you can indeed pop into your local Starbucks for a bag of coffee grounds. In some stores they’re already on display, and in others you have to ask behind the counter for them. Interesting to know about the wormeries!

Member
Tychique Kode says:
7 January 2014

Hie, Veronicca
I’m Tychique just want to appreciate this recommendation of used coffee, I think it’s the best suggestion to follow…
Thank you!

Member
Chris Male says:
20 August 2014

If coffee grounds are acidic and wood ash (and presumably paper ash) is alkaline, then mixing them together should leave them neutral and suitable for all applications. I put them in my potting compost and mix them in with my greenhouse soil.

Member
Brooke says:
31 January 2015

Hey Veronica,
I am doing a science experiment on whether or not tea and coffee grounds can help the growth of peas and beans. We added half a cup of grounds and soil. So far the tea seems to be molding over the plants. The coffee is also pretty slow. After some research I have figured the rotting may be blackheart disease or the acid levels may be too high, as the coffee averages a 5.0 pH level and the soil a 6.0-7.0 pH level. I’m not sure which one is more likely. Do you have any information on this or know what may be happening to the plants?
Thanks:-)