Using spent coffee grounds for gardening is cost-effective and a great way of ensuring your cup of coffee is extra sustainable! However, there’s quite a bit of conflicting information about how this can be done, so we thought we’d address the myths and facts about the most common uses for coffee in the garden.
Coffee Grounds as Compost
Using coffee as compost material is fairly straightforward, simply chuck your used grounds into the compost heap and let nature do the rest. When doing this, it is important to keep in mind how the coffee affects the composition of your compost! Used coffee grounds are a type of green compost, which means they are rich in nitrogen. Other sources of green compost are things like grass clippings, fresh fruit/veg scraps, and garden weeds. Your compost heap should ideally be composed of the correct ratio of green and brown compost, which is roughly 1 part green to 3 parts brown – but make sure to check the best ratio for your purpose! Sources of brown compost are rich in carbon, so things like dry leaves, shredded cardboard & paper, and wood chippings. However, for reasons outlined below, spent coffee grounds should not make up the entire portion of green compost.
Coffee Grounds as Fertiliser
Within gardening circles and online forums/blogs, there’s a lot of conflicting information about whether spent coffee grounds can be used as an effective fertiliser. A deeper look at published academic articles and a few anecdotal articles shows that coffee grounds, even spent ones, don’t always make the best fertiliser.
Caffeine and Plants
Many people enjoy their morning coffee for its ability to wake them up and feel ready for the day -thanks to its caffeine content. Yet caffeine is moderately harmful to plants as it can stunt their growth by preventing the production of essential proteins. In fact, the reason plants such as coffee and tea plants produce caffeine is as a defence mechanism; it is harmful to most animal and plant species. Don’t worry though – although too much caffeine is also harmful to humans, most healthy adults can have up to 400mg (about 4 cups of strong coffee) per day without harm.
Returning to plants, even spent coffee grounds retain enough caffeine to cause harm and so do not make a good fertiliser. However, there are natural ways to process the grounds to reduce the caffeine levels to unharmful levels, and if done correctly, composting is one effective method. Vermicomposting is another method which is a form of composting using worms. Although this is best done in moderation, as too much can be harmful to the worms.
Alfie coffee isn’t like most other coffees on the market. For one thing, our coffee is lower in caffeine than most since the beans we use are from organically farmed berries picked at the perfect level of ripeness so that they’re naturally low in caffeine. Therefore, if you’re using our coffee then the spent grounds can be used in the garden, in fact Paul, Alfie’s Director and Chief Roaster, uses the grounds for fertiliser in his garden to great success!
Coffee Grounds as a Slug Repellent
Since the caffeine in coffee can be toxic to some plants and animals, some people use it as a natural snail and slug repellent. There is some anecdotal evidence of this being effective, so experiment with sprinkling it around the area you want to protect and see if it works for you. Additionally, since caffeine prevents plant growth it can also be used as a weed killer as long as this is not done too close to any plants you’re trying to grow.
We hope this clears some things up about how coffee can be used for gardening, but as always, it is important to do your own research to ensure the health of the particular plants you’re growing!