Jian Liu in defence of using spent coffee grounds

Jian Liu, from Camberwell, discusses her use of spent coffee grounds in her garden. In May 2021, Jian’s garden featured on Gardening Australia – watch the 7 minute segment.

I want to share my experiences creating a flourishing and productive suburban garden built on coffee.

To set the context, our native garden soil in our backyard is basically grey beach sand, devoid of nutrients and life. Nothing could grow in it without significant improvement. We also want to grow plants in a way that’s sustainable, and not import masses of purchased bagged compost. I set about on a mission of bringing our soil to life. Enter the coffee.

Our entire garden is built almost entirely on coffee grounds and husks (quite ironic for two non-coffee drinkers!). And I’m not talking sprinkles of grounds from a local cafe. Rather, we have gotten two bulk deliveries of coffee grounds (two vans full around 1-2 cubic metres each time) from Reground the past two years. In addition, a relative of mine works for a coffee roaster and brings back weekly sacks of coffee grounds and husks, which are used in the garden. I’m talking mountains of coffee used in a standard-sized backyard.

While they’ve gotten a bad rap in recent years (I first heard about the potentially detrimental effect of coffee grounds in Leaf, Root & Fruit’s experiment in 2019 and, more recently, in Sarah Hardcastle’s ABC interview), my experience is that, used in the right way, they can dramatically increase soil fertility.

We have used them to transform our grey sandy soil into soil capable of supporting healthy plants, in just a few short years. The various photos show a garden bed right behind our shed on which about 10cm of coffee grounds were placed onto the surface of the soil. This tiny area is now capable of supporting 4 tomato plants, 6 beans and a pumpkin, with the only soil amendments being coffee grounds, husks and horse manure. All plants flourish.

My first use of coffee was around my blueberry plants (due to the view they are acidic), and I have been using them for the past 10 years on my blueberries – which produce abundantly and have flourished.

Coffee grounds should not be used as ‘soil’

While coffee grounds look like soil, they should never be treated as such. So, for example, mixing into a potting mix for young seedlings is an experiment designed for failure. Rather, coffee grounds need to be thought of as an un-decomposed product – just as you wouldn’t put chopped up food scraps or un-composted manure into a potting mix, you also wouldn’t use coffee grounds in that way. Young seedlings are particularly sensitive to soils that are too rich / not fully
decomposed.

How we use coffee grounds with success

We use coffee grounds liberally as alternating layers when creating lasagne beds, and we top dress fruit trees and garden beds with coffee grounds. In this way, they are not getting mixed into the soil (you shouldn’t be digging your soil between seasons anyway). Instead, they are layered on top much like a mulch, or the chop and drop method in permaculture. Gradually the coffee grounds will compost on site and, once nicely decomposed, the worms will bring the goodness down to the plant roots. You will find that wherever you put coffee grounds, the worms will follow – hence we also use in our worm farms and compost bins. And no, they are not acidic at all once broken down – I have pH tested it many times.

Using them is actually remarkably simple – just dump around fruit trees and on the top of soil, no mixing required. Or use in worm farms and compost bins to accelerate your compost.

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In summary, coffee grounds are a massive by-product of our caffeine-addicted society. Used in the right way, my experience is that they are very beneficial in the garden. They are free, abundantly available, and a powerhouse of nutrients for the soil and the life within the soil.

How ironic that I, a non-coffee drinker myself, am extolling the benefits of coffee for the garden!