Grounds in the Garden
Words : Ben Hepworth & Sheena Marsh
Reduce, Reuse, Recycle, Repurpose
Like all businesses, the coffee industry has a carbon footprint which adversely impacts on our environment. Having said that, collectively, as responsible roasters and consumers, we can do our bit to ensure we offset as much of this footprint as possible.
In the UK, we consume 95 million cups of coffee every single day and the unavoidable by-product of this consumption results in half a million tonnes of wet coffee grounds. Subsequently these end up in landfill, emitting harmful greenhouse gasses as they decompose, including methane which is known to be more harmful than carbon dioxide. Not only this, but as coffee grounds contain oils and other compounds, in landfills, this causes the acidity in the soil to increase, releasing a liquid, (acidic leachate) damaging the surrounding soil.
There are many ways in which used coffee grounds can be recycled, a google search will provide you with many wonderful ideas however, the one that we promote and recommend is to repurpose them in your garden.
In order to offer the very best advice, we spoke with Sheena Marsh, founder of Oxford Garden Design and writer for the Oxford Times’ Limited-Edition magazine. Sheena has also appeared as the Gardening Expert on BBC Radio Oxford as well as taking part in the Channel 4 ‘Great Garden Challenge’ programme, filmed at Blenheim Palace. Sheena has kindly offered up the following advice, hints and tips on what we can do with our spent coffee grounds in the garden.
Using spent coffee grounds as compost is a very sensible choice. Just add them to the heap and let the compost bin do its job. If you choose to drop coffee grounds in the compost bin, remember they qualify as green compost material. You may want to balance it with brown compost material (like dry or dead leaves).
The Acidic Leanings of Coffee.
Those considering adding coffee directly to the garden will likely worry about the acidic content of coffee. That’s a reasonable approach. Fresh coffee grounds do tend to be acidic, even if on the mild side. Spent coffee grounds, on the other hand, veer towards the neutral. The expected pH value of used coffee grounds is 6.5 to 6.8.
For reference, a pH of 7 is considered neutral. So, calm your worries on that count, and let the coffee do its job. However, do try to match coffee with plants that love more acidic soil. Which brings us to the next point.
Using Coffee as Fertiliser.
Adding coffee grounds directly to the soil as a fertiliser can be a good option. Coffee grounds are rich in nutrients, especially nitrogen. They also have some amount of other nutrients like potassium and phosphorous. Overall, this means that adding coffee grounds to your garden can work fairly well as a fertiliser.
Coffee should be spread in a thin layer, rather than being clumped in one place. Spreading it as a thin layer not only spreads out the nutrients, it also reduces the chances of caffeine affecting one particular spot of the garden.
Fresh grounds have more caffeine, but the content of used grounds is debatable. The regular inference would be to assume that used grounds have lower caffeine. However, that is not always true. There’s a good chance that at least a portion of the grounds has high caffeine content.
Fresh Ground Coffee as Fertiliser.
Unused ground coffee as a fertiliser is an expensive option, especially when compared to conventional options. Used coffee grounds are a waste product put to use in gardening. Fresh grounds have their regular use and I’d suggest avoiding them unless you think it necessary.
When using fresh grounds, don’t forget about the caffeine and pH levels. Spread it as a very thin layer. Give preference to acid-loving plants like hydrangeas and blueberries. Root vegetables like carrots and radishes respond well to the acidity.
When adding caffeine, keep note of the expected effects. For example, avoid adding any caffeine to plants that are germinating. Freshly seeded areas should be avoided as well. Fresh grounds, and caffeine in general, have allelopathic properties. This can stunt plant growth and do more harm than good.
Some people suggest using decaf grounds, both for new and used grounds. The idea is that the lack of caffeine in the grounds can avoid associated problems.
Removing Weeds and Pests.
Here’s one positive of adding fresh grounds and caffeine to the garden. Strategically placed, the caffeine provided by fresh grounds can be used to deter the growth of weeds. This process hinges on the allelopathic properties of caffeine.
Another useful aspect is that caffeine pushes back several pests. Chief amongst these are slugs and snails. It is worth noting that while these critters avoid coffee, it is not exactly a fool proof method. Slugs don’t exactly like coffee, but they won’t run away from it either.
Interestingly, coffee grounds also discourage pets from entering the area. Cats, for example, avoid exposure to caffeine. This will keep the garden free of the cat and stop it from becoming a litterbox! Some extra care is needed if your pet is a dog and has a penchant for eating or licking random things. In such a case, avoid caffeine for the dog and consign it to the compost heap.
Apparently, earthworms love coffee! Adding some coffee grounds to the worm bin can attract more worms. You could also occasionally add used coffee paper filters to the bin. It’s a rather simple method to get some good results.
Coffee Grounds as Mulch.
Mulching is very beneficial to plants and every serious gardener considers the option. But then getting a hold of mulch isn’t easy! Getting coffee grounds to play that role seems like a no-brainer. The results, however, do not agree. Many gardeners have found that using coffee grounds as mulch can be very destructive to the plants.
A different approach is required with coffee grounds. A thick layer of mulch with coffee grounds will lead to caffeine-rich soil and stunted plants. Instead, consider mixing coffee grounds with other organic material. Another possibility is to add a thin layer of coffee grounds on the soil, and then rake it to mix it all up causing the coffee grounds to spread and not lump together. This way, the plants get undisturbed water supply, and the caffeine content is not overwhelming.
When used correctly, coffee grounds can be a great addition to your garden. Many gardeners find it is a safe, natural, and effective way to boost their gardens without using harsh chemicals or pesticides. If you’re a keen gardener or an eco-conscious individual and want to do your bit to help intercept coffee grounds heading for landfill, speak with your local coffee shop who I’m sure would be more than happy to keep their used grounds aside for you to collect to repurpose in your garden, making it a win for them, a win for you and a win for the Earth.