Guide written by:
John, Passionate gardener, Cambridge
Coffee grounds are a by-product of everyday life. Luckily, they also come in very handy around the garden whether used as a slug repellent, fertiliser or a source of micronutrients. In short, there's no excuse for them ending up in the bin! Follow our guide for the best ways on reusing your coffee grounds.
- Organic fertiliser
Using coffee grounds as a natural fertiliser
Coffee grounds are an excellent natural fertiliser as they are rich in nitrogen (around 2% by volume) and minerals such as potassium, magnesium, phosphorus and copper. As an organic product, coffee grounds decompose slowly and release minerals gradually to ensure a steady flow of nutrients over time. They are also a great source of organic matter.
The easiest way to reuse coffee grounds is to simply spread them over the soil at the base of your plants. Alternatively, you can add some coffee grounds to your watering can and use the mixture to water your plants. You can also spread them over the surface of your potted plants and rake lightly to refresh the top layer of soil. If you're looking to repot a plant, coffee grounds will be a welcome addition to potting soil. Otherwise, you can dig them into soil around the garden with some shallow hoeing.
The main plants that will benefit from coffee grounds include green plants, potted plants with flowers and all plants that like acid-rich soil (such as hydrangea, azalea, rhododendron and heathers). Coffee grounds have a pH level of around 6.2. For plants that are acid-sensitive (such as vines, melons, columbine, cabbages, etc.) you can alter the acidity of the soil by adding some crushed oyster shells or ground-up egg shells.
Coffee grounds for compost or vermicompost
Coffee grounds can, of course, be added to your garden compost pile along with the paper filter if it is biodegradable. It is also possible to recycle your coffee grounds to make vermicompost and give your worms a real treat!
Using coffee grounds for seedlings
You can create an excellent growing substrate for your seedlings by mixing one part coffee ground with one part garden soil. This mixture can also be applied to potting soil for your trays, pots and planters.
Or why not use it to refresh the top layer of your soil? Simply spread it over the surface of your containers or around the base of trees and shrubs on balconies or decks.
Using coffee grounds to evenly distribute your seedlings
Firstly, you need to dry out the coffee grounds by spreading them over a surface; this will help to prevent mould. Next, mix the grounds with the seeds you want to sow. The colour of the coffee grounds is different to that of soil which will allow you to spread an even strip of grounds along your grooves when seed drilling. In turn, this allows you to space out your seedlings more evenly and encourage them to grow at a more steady rate.
Another advantage of this method is that coffee grounds help to deter harmful insects such as carrot flies.
A natural method for repelling slugs and ants
While less effective than wood ash, coffee grounds can be spread around plants to protect them from slugs and snails as they do not like to slide over this type of material. This method will. however, lose effectiveness after the rain. Coffee grounds can also be used in combination with other measures to create a natural barrier against other plant-eating pests.
Coffee retains its odour for a long time so it can be spread over pathways and areas populated by ants. That said, this method tends to provide mixed results.
Growing mushrooms in coffee grounds
In recent years, increasing popularity of urban agriculture has led to various methods of growing mushrooms using coffee grounds collected from coffee shops, canteens, restaurants and so on.
Mushrooms can, for example, be farmed on a substrate of damp cardboard (which is rich in carbon) and coffee grounds (to provide nitrogen and other minerals).
Coffee grounds as a carrot fly repellent
There is also anecdotal evidence that coffee grounds can be used as a repellent against carrot flies. Simply mix your seeds with dried coffee grounds before drill sowing them in channels. This also helps to encourage steady seed growth.
Guide written by:
John, Passionate gardener, Cambridge, 47 guides
When I was young, I was already working in the family garden. Perhaps that is where my interest in plants and gardening came from. So, it was logical for me to study both plant biology and agronomy. At the request of various publishers I have, over twenty-five years, written many books on the subject of plants and mushrooms (a subject that is close to my heart).They were mostly identification guides at first, but shortly after they were about gardening, thus renewing the first passion of my childhood. I have also regularly collaborated with several magazines specializing in the field of gardening or more generally in nature. There is no gardener without a garden, I have cultivated mine in a small corner of Cambridge for the last thirty years and this is where I put into practice the methods of cultivation that will I advise you in as well.